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Reproduced for NASA by the NASA Scientific and Technical Information Facility

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FFNo 672 Aug 65 1111111111111 1111 1111111111111111111111111111' NF01723 ,.. '.. 3 1176 01327 9253

5030-471

0," , Electric & Hybrid Vehicle System , Research & IJeofeIopment Project -'-_. r

(H1Sl-CR-1637Q4) AERODYHA5IC DESIGN OF N81-129q3 ELECTRIC lND HYBRID VEHICLES: 1 GUIDEBOOK (Jet Propalsion Lab.) 92 p H~ A05/!P 101 CSCL 13F Unclas G3/S5 29312 Aerodynamic DeSign of Electric and Hybrid Vehicles: A Guidebook

D. W. Kurtz

September 30. 1980

Prepared for U.S. Department of Energy "Through an agreement With National Aeronautics and Space Administration oy Jet Propulsion laboratory Cahfornla Institute of TeChnOiogy Pasader1a. California

(JPL PUBUCATION 80-69)

1/11-12-91/,3# 5030-471 Electric & Hybrid Vehicle System Research & Development Project

Aerodynamic Design of Electric and Hybrid Vehicles: A Guidebook

D. W. Kurtz

September 30. 1980

Prepared for U.S. Department of Energy Through an agreement With National Aeronautics and Space Administration by Jet PropulSIOn Laboratory California Institute of Technology Pasadena. California

(JPL PUBLICATION 80-69) ---

The research described in this publication vas carried out by the Jet Propulsion Laboratory, California Institute of Technology, and· vas sponsored by the United States Depart.ent of Energy through an agreement vith NASA.

This report vas prepared as an account of work sponsored by the United States Covern.ent. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their e.ployee~, ..kes any varranty, express or implied, or assumes any legal liability or responsibility for the accuracy, co.pleteness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

This document is available to the U.S. public through the National Technical Information Ser~ice, Springfield, Virginia 22161

-- PREFACE

The E1eetrie and Hybrid Vehicle (EHV) Research, Deve10paent and Demonstration Act of 1976, Public Law 94-413, later ..ended by Public Law 95-238, established the governaenta1 EHV poliey and the current Depart.ent of Energy EHV Progra•• _ The EHVSyatea Research and Deve1o~nt Project, one e1e.ent of this Progr.. , ia being conducted by the Jet Propulsion Laboratory (JPL) of the California Institute of Techno1osy throush an asreeaent with the National Aeronautics an.! Space Ad.inistration. An objective of the Progra. is to develop the technologies required by the EHV indust.ry to successfully produce vehides with widespread acceptance. One of those technologies reqU1.rLng developaent is vehicle aerodyna.ics. This guidebook presents the tools. stntegies and procedures involved in the design of aerodY'idlllic31ly efficient vehides. The lIIethodology is intended to be useful to designers possessing little or no aerodyna.ic training.

iii -A typical present-day subcOlipact IBV, operating on an SA! J227a D driving cycle, consuaes up to 35% of its road energy require.ent overca.ing aerodynaaic resistance. The application of an integrated systea design approach, where drag reduction is an iaportant design par_ter, can increase the cycle range by .ore than 15%. This guidebook highlights a logic strategy for including aerodynaaic drag reduction in the design of electric and hybrid vehicles to the degree appropriate to the .ission require.ents. Backup information and pr~cedures are included in order to iaple.ent the strategy. Elements of the procedure are based on extensive wind tunnel tests involving generic subscale models and full-scale prototype EHVs. The user need not have any previous aerodynaaic background. By necessity, the procedure utilizes many generic approximations and asauaptions resulting in various levels of uncertainty. Dealing with these uncert.intiea, however, is a key feature of the strategy.

PRECEDING PA~r a ...... WU\RK NOT AlMru

v COHl!NtS

I. ~DOCTIOR ------1

It. APPROAC1l -- 5

Itl. AERODYlWfIC DESIGN LOGIC PAtH ------7

A. LEV!t. 1 DESIGN ------.------8

B. LEVEL 11 DESIGN ------9

C. LF.VEL 111 DESIGN -_.----, 11

D. CONCLUDING llEHAlUtS ----.------14

IV. REFERENCES ------15 v. BIBLIOGRAPHY ------.•------17

A. GENERAL AUTOHOTIVE AERODYNAMICS ------17

B. FACILITY TESTING ------22 C. ROAD TESTING ------. ------25 D. WIND NOISE ------,------26 E. VENTILATION AND ENGINE COOLING ------27

F. STABILITY AND HANDLING ------27 G. GENERAL BOOKS AND PROCEEDINGS ------28

APPEtroIXES A. EFFECTS OF ASPECT RATIO AND FINENESS RATIO ON THE AERODYNAMIC C1lARACTERISTICS OF AUTOMOBILE SHAPES ------29

B. FOUNDATIONS OF AERODYNAMIC DESICN ------35 C. A REVIlOll OF GENERAL AERODYNAMIC DRAG PREDICTION PROCEDURES, APPLICATION, AND UTILITY ------55 D. APPLICATION OF AREA-DISTRIBUTION SMOOTHING PROCEDURE~ TO AUTOMOTIVE AERODYNAMIC DESIGN ------69

PRECEDING PAUL BLANK NOT FfUEIl vii E. ESTD'ATIRC DUG CltAIACTDISTICS III YA1l lOR AJmItOIIU SHAPES ------77 P. DITDKlIfATIOH OP DUG vnm WEICIITllC PACt'OIS FOIl VEHICLIS OPDAnllG m AKlIDT VIlIDS ----.---- 81

Pisure•

1-1. toad En~r~1 Co.ponent Split Over the SAl J227. Schedule n Driviq Cycle ------. 2 1-2. Projected Vehicle lanae Over the SAE J227. Schedule D Drivinl Cycle a •• JUnction of Various Par_ters ---n_ - 2 3-1. Aerodynaaic De.iln Lolic Path, Level I ------7

3-2. Aerodynaaic Design Lolic Path, Level II ------9 3-3. Aerodynamic Design Logic Path, Level III ------12

viii · SECTlOR 1

IKnODUCTIOR

As an auto.obile .oves along a road surface, the resultinl displac~nt of air gives rise to various forces and .a.ents. DependinR upon the aissioD, or driving cycle, the aerodynaaic drag experienced by a typical electric or hybrid vehicle (SHY) ..y consuae a sisnificant portion of the energy supplied by the propulsion systea. since the SA! J227a D cycle has been sUllested as being representative of an electric passenger vehicle aission, it is proper to consider the iapact of aerodyn.. ic design upon the total road enerKY requireaent for that cycle. Figure 1-1 shows the cycle energy split as a function of drag area, CoAl' for a typical subca.pact ~IV weighing 1350 kg (3000 Ib) and having a rolling resistance coefficient of 1.2% of the vehicle weight (rolling losses include those due to tires, bearings, gears, brakes, etc.). Current subcompact-clas~ vehicles have drag areas of about 0.9 m2 (9.7 ft~) which means that the aerodynamic component may be responsible for about 35% of the total road energy consuaed over this cycle. Because of progress recently demonstrated by the automotive industry, it is reasonable to expect that, with vigorous design efforts, a drag area of 0.55 m~ (5.q ft~) may be achievable. The benefit of such a 40% reduction in the CDA related to an electric vehicle (EV) is shown, in ~igure 1-2, to be nearly a 20% improvement in range. To achieve a similar benefit via reductions in the other components \.roulJ require about a 50% reduction in the rolling resistance coefficient to 0.6: (a rather unrealistic value) or a 22% reduction in vehicle weight (the removal of an additional 300 kg from an already lightweight vehicle woulJ be ver~ difficult). These examples, although simplified, tend to demonstrate the potential benefits from, and justification for pursuing aerodynamic resistance reduction.

F.fficient aerodynamic design is an elusive accomplishment. Automotive aerodynamics is presently at the stage aircraft aerodvnamics was 50 ~ears a~o. It is, however, a fundamentally different problem since a road vehicle is a bluff body, having oany local areas of flow separation, and operates in the presence of the ground. Recognizing the need And potential benefits to be derived from a clearer understanding, the SAE recentl~ commissioned the development of an automotive aerodynamic research plan (Reference 1-1).

1 The drag coefficient, CD' is nondimensional and is defined as

CD • Drag Force/(1/2 x Air Density x Velocity2 x Frontal area).

The frontal ar~a, A, is the vehicle's projected area including tires. and suspension members but excluding appendages such as mirrors, roof racks, antennas, etc. The velocity is the relative speed between the air and the vehicle. .. . i

> " ,... -~ g...... z :s\J .. '0 POUNnAL Coo' Of TYPICAl CoA Of CUIIENT SUlCOM'ACT SfDAN SUlCOM'ACT SEDAN

O~ __~~ __-L~ ____~~-L~~ __~ 0.2 0.4 0.6 0.1 '.0 '.2 CoA.-2

Figure I-I. Road Energy Component Split OVer the SA! J227a Schedule D Driving Cycle

20

... '5 ~ ~ 0 IASfUNE VALUES ~ WEIGHT ,3.50,,- -.N ItOWNG '0 Z ItESt ST ANa '.2' ... CoA 0.9,.2 ~ x~ v 5 ~

10 ~ CHANGE IN I'AlAMET£It

Figure 1-2. Projected Vehicle Range Over the SA! J227a Schedule D Driving Cycle as a Function of Various Paraaetera

2 ------

This plan calls for the expenditure of 2S aillion dollars oyer a five year period in order to brina the state-of-the-art of auta.otive aerodyna.ics into line with other enaineerina disciplines. The sheer size and co.ait.ent indicated by such an andertaking gives one so.e perspective into the difficulties and uncertainties inherent in auto.otive aerodJnaaic desian today. This aerodynaaic design auidebook utilizes a logic strategy for designing aerodynaaically-appropriate electric and hybrid vehicles with current aerodynaaic understanding. Its intended user is the vehicle designer and builder who has little or no aerodyn.. ic background. By necessity, the procedure utilizes ..ny seneric approxiaations and assu.ptions resulting in various levels of uncertainty. Dealing with~these uncertainties, however, is a key feature of the strategy.

3 SECTI0R 11

APPROACH

The approach is to develop an aerodynaaic design sequence composed of logical path ele.ents which provide a strategy and guide through progressively .are refined levels of design. The process of developing this logic path exposed .any technological gaps and information voids inherent in various path elements. In the course of this endeavor, studies and test programs were undertaken in order to alleviate the uncertainties and to provide the necessary tools and procedures required to implement the strategy.

A limited aerodynamic data base was developed by wind tunnel testing 20 electric, hybrid and subcompact vehicles (Reference 2-1). These results were used to extend, develop and refine drag prediction techniques; to develop generalized relationships between drag and yaw angle (the angle between the relative wind and the longitudinal axis of the car); and to quantify the uncertainty in subscale-to-full-scal~ wind tunnel test correlations.

Because of battery paCkaging requirements, EHVs may be subject to somewhat different constraints than conventional internal combustion (IC) engine vehicles. For instance, owing to the use of a central battery tunnel, a small vehicle may be unusually wide or long. A series of subscale tests was therefore performed to determine if aspect ratio and fineness ratiol were important aerodynamic parameters.

~ince any road vehicle rarely operates in a zero-wind environment, an analysis of the driving cycle-dependent effects of ambient winds on vehicle drag was performed. This is a necessary extension to aerodynamic drag evaluations and should be included in vehicle computer and dynamometer simulations.

Finally, it was necessary to evaluate simplified general aerodynamic design principles in order to determine the confidence levels resulting from their application.

IAspect ratio CAR) is defined as hody height divided by width, and fineness ratio (FR) as length divided by effective diameter (of equivalent area circle). SECTION III

AERODYlWfIC DESIGH LOGIC PATH

The logic sequence incorporates path ele.ents which terainate at one of three levels of design. These design levels are progressively .are refined and are successively characteriz~d by a higher probability of yielding a low drag design. This logic path, then, defines the procedural ele.ents required for the design of an aerodynamically efficient EHV. Technical backup information is supplied in the various appendixes in order to facilitate applying the .,rocedures. .

The strategy which governs the use of·these procedures, originates in the develo~nt of a design acceptability cri~erion. Consider the design logic path beginning in Figure 3-1. Note that the .initial steps are the definition of the mission use or cycle requirements, and the resulting deteraination of the aerodynamic acceptability criterion. This is 'he heart, the driver, of the entire process. It is imperative that one carefully characterize the mission performance objectives for which the vehicle is being designed at the outset. Once this is established, a thorough trade-off analysis must be ..de in order to dete~ine the relative sensitivities of the various physical parameters. The result of such a procedure is analogous to that presented in Figure 1-2. There, the mission perforoance objective was to maximize range over the SAE J227a Schedule D driving cycle and the resulting sensitivity analysis was

SENSITIVITY OF MISSION MISSION REQUIREMENT TO DRAG DEFINITION (ACCEPTABILITY CRITERIA)

PACKAGING REVIEW DEVELOP LAYOUT GENERAL DESIGN & vEHICLE AERO DESIGN SKETCHES ENVELOPE PRINCIPLES NO

Figure 3-1. Aerodynamic Design Logic Path, Level I

7 performed (using a si.ple vehicle,computer su.ulation) around a postulated baseline vehicle1• It should be emrhasi2:ed that these sensitivity relationships are a strong function of the mission require_nts.

For instance, if one were designing a postal vehicle or milk delivery truck whose aission is characterized by numerous starts and .. stops and virtually no constant or high speed cruising, the energy efficiency (or rang~) would be almost independent of the aerody~ic drag. On the other hand, if a high-speed c'OIIIIluter vehicle characteri~ed by relatively few stops is being designed, the range is a ver~ strong function of the aerodynamic drag. After these parametric sensitivities have been determined for the design mission, a target value and tolerance limit for the vehicle's aerodynamic drag may be established.' This becomes th'e, "acceptability cri.terion" against which various designs will be evaluated thrJughout the remainder of the procedure.

A. LEVEL I DESIGN

The first level of design (Figure 3-1) focuses prtmarily on the ~ross and ~uperficial design processes characteristic of a designer's sketchbo.)k. This may be called a subjective design analysis and is an ~ssential beginning to any design process. First, the packaging ta~'Ollt and vehicle envelope must be determined~For Ie engine vehicle desi~n, this is influenced primarily by the passengers, payload and Jrivetrain \·ollime requirements. For electric vehicles, the significant additional volume required for th~ traction ba~teries could impact the normal body proportions to such a d~gree that any first order aerodvnamic influence needs to be addressed. That is, with the .l.Je of a" central battery 'tunnel. a small car may be unusually wid~: or with batteries located beneath s~ats (or unJ~r the fh1orboar.t), the vehic1~ mav be lInu~uallv tall. The aerlldvnamic consequence is ~uch that th~ specific ef~ects of aspec~ ra~io and fineness ratio can be identified and should be considered. Su~scale test~ were conducted on a family of automotive shapes in order to quantifv their influence on drag. The ~eneric .trends and r~lationships appear in AppendiK A. After iterating this trade-off within th~ bounds of the d~sign theme and q~ility requir~ments, the ne~t path ~l~ment ma~ be ~ddressed. This is characterized as a ~t~nt>ral review and under::lt.'lnding of the sour:!!:! .. of automotive drag and some "f the basi.: principles involved in o:!fficient 3t!rodynamic ,tesign. .-\ bri .. f treati,;e on the subje.:t ,l['pears 'in .\ppendilt 3.

~ith th~ packaRinK 'envelope and general aerodynamic Guidelines in hand, tIle first !:JoJy Jesign "ketcht'S ':.In begin to evolve. '\s a styling theme is Jo:!v .. loped and refined. tho:! final sketches are review .. d and, after 8ev .. ral it~rations. proposed design drawings are

IThe sen~itivitv analysis can b~ don~ for Jther performan.:e objectives 3S ~ell {e.g., acceleration, ~r3deability. etc.'.

8 selected. The aerodynaaic acceptability criterion, deterained in the first steps, is now applied. Rote that no quantitative aerodynaaic analysis has been performed to this point; therefore, there is considerable uncertainty as to the value of the dral coefficient ~presented by this desiln. The probability of it beinl an exceptionally low-dral desisn is quite ...11. If, however, the sensitivity analysis performed earlier indicated a weak dependence of the perforaance objective (e.I., range) on the drag level, the large uncertainty ..y be perfectly acceptable. That is, there would be no justification for refininl the aerodynaaic desisn any further, and the Level I ~esign would yield a vehicle having -appropriate aerodynamic ,desisn" cOllDensurate to its lIlission. If, on the other hand, the sensitivity analysis had indicated a stronger dependence on dral level and the resulting acceptability criterion had required that the drag coefficient be no greater than, say 0.5, then Level I Design, with its Characteristically large uncertainty, would be unacceptable. If such were the case, continuation to the next level of design would then be required.

B. LEVEL II DESIGN The second level of design (Figure 3-2) can be described as an empirical design analysis utilizing procedures and practices which are generically effective. The final sketches resulting from the Level I design procedures become a baseline or stravaan design for the Level II analysis.

DEVELOP AREA STRAWMAN GIlADIENT DESIGN ANALY$IS

MODIFY GRADIENT "<0 SPECIFIC SMOOTHING AREAS MODIFICATIONS

• YAw CHARACTERISTIC I---.j PREDICT CO" AND 'NINO wT. AND UNCERTAINTY ~NALYSIS

CONTINUE

Figure 3-2. Aerodynamic Design Logic Path, Level II

9

.. ,

I Drag predicti~n for automotive shapes is 1enerally unreliable in an absolute sense; its rl!al v.slue lies in the pc,,~:,'ti1ity of ' highlighting various drag producing elements. These drag prediction • procedures (Appendix C) are a drag buildup approach (References 3-1, 3-2, and 3-3). That is, the vehicle is divided up into about a dozen regions and the Jrag contribution from each region is then determined by examinin~ the hlCll1 shape characteristics. 8y nQting the rp.lative ma~nituJe ~f various drag elements, th~se regions deserving of more • attenti.,n :Ire id.mtified. Any necessary IDOdifications can be factored in an.l rt>eV.1lullte,1 in an iterative mann .. r.

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,to ~. t

•

~. L~V~L ttl nESIGN

Th.· third :md 1II,'st-refine,1 level of design is 3n experiot.'ntlll Ilr,'ct>:ts rL'lyin)t heavily on insight and experience. Persons having :t~~. knowl .. ci~~ of experimental automotive aerodynamic techniques should h .. involved (e.g., a consult3nt) or little can be gained by this proces:t. tn 3ddition, 4 relatively 13rge financial commitlllent mllst hp. IIn.lertaken in order tll proceed. Up to this pllint. no pro.:urelllent!'& h.1vt.' b",'n required. no hardwar,· has been created and the t"t.l1 .-ff"rt "xpt'nded h.1s ht!l'n 4 few lIIan-months. Building lIIodels and Il,'rf,'rmin~ .h·v .. h1pmental w'nd tunnel test:t m.'y incre3se these ~ .. rodyn4I11ic desi~n r .. 14ted cO:tts by .'I factcr of 10 or more. If that l,·v .. l "f t'xJwnditure is w.1rr4nted. t .. ve1 Itl Design should be in i t i:ttt'd (F i !~ur., J-.1).

IItili:o:in!~ th.· r":mlts "f th.· tevel II desiltn proc,·s:t." subsc41e win.1 tllnn.·l 1110,1 .. 1 is constructed. Since the objective of these tests is t" fin.· tlln,· th,- ...·5i~n •.1 modt' 1 with th .. ':3p.lbi1ity of in,:,'rp,'r:ttin~ :tuhtlt· ch.lng,·s is required. A spe.:i.11 c13Y surf.lce 1.1id ,'n ;t ri~id substructur," h3s prllved to be the IIIllst pr3ct Lca1 appro.leh. 1"'" 1:11'.1.· 1 5(".11,' :111,1 support dt't4 i Is .'Ire fune t Lons 0 f the spec i fic wind tllnl1,· I h,' i 11~ IIs,·,I. (~u.lrter to th r~.·-e ighths scale have b"en th~ m,'st ~"l'ut.lr.1 It i~ hi~hl~' rt!e,'an .. n"~d that tht! l .. vel t>f 1110.1.'1 d~t

Itn ,'r.It'r t" "l1nlml~" contr"versi.l1 wind tunnel wall corrt!ctions. tht! !:IOdel ~c31 .. shmlld be chosen such that the mod .. l cross-sectional are3 be no ~ore th.:ln ~~ of th .. tunn"l cross-sectit>n41 art!a (above the ground plane).

II TO SUCC(SSfULL Y NOCHD J ItEQUIIlS SOM( (XPlIllNCE • ~IN AUTOMOTlV( AliODYNAMICS

DltAG BUILD wIND TUNNU N(DICTION MOOn nsn AND UNCliTAINTY

MODEL TUNING

Fi)oture 3-3. Aerodynamic Design logi.: Path, level Itt

:\ '!llnlmUIII of 15 to 20 win,t tunnel occupancy hours will be r"<1l1irt'J for t~!'Itin~ of the preliminary model in origin3l .1nd 'Iti,:htlv-tn".lified f,,"u (sometime. called, "aerodynaMic tuning"). Thi,.; is in IIdditi.,n t" initial !'Ihakedown runs to check out the 1II0dei ,·,'n!ltrllC'ti.'n. vt'rifv that the data acquisition and tunnel systems are ,'!',-r.lt i'N !,r<1rt'rlv lind to qU:lntify the effects of Reynolds NUlllber (!l~n!litivitv ~f ~~rodynamic coefficients to air speed). Usu~lly. th~ ~ff~C't i!'l !llll~ll 3nd ~ conv~nient tu~nel lIir speedl can be 3dopted f,'r th,' nO'lt of tht' te~t. If II re~l-tim.! datil reduction 5vstelll is I"rovi,I,'·'. tht' m"Jel .tr:a~ c(\ .. ffic:ient can be continuously ~nitored. T"!lt,; !lh,'1I1,. b., Y't>rf"rmed :at y:aw IIngles up to IIbout. 40 de~rp.es in "r.l.'r t., ,1.-\"'1.,1' th., inf•• t"t!I.lt ion nt'cess:ary f,'r th .. '·,ind Il€'i)tht inr. .m.lh·,;i.; L\pr.-n,lilc: Fl. Arriving f:act,'rs ttl .1cc,lunt f,'r !lub';C.llt' t" fllll-!lC31~ C'prr~1~ti~ns.1 II dra~ rredicti~n 3nd 3!lsoci3t~J Ullc.'rt.lint\· IIIl1\'" b" ,I.'t.'rmin~d. The acct"pt3!li\ ity crittc'rion is .,ppl i .. ,t ~,; .I~.;cri~~j ~3rli .. r.

l f th.- .:ritt'ri,)O wer,' innedilltety satisfied :at this rt,int. tht' I",;i~n !'n'Cl'!l!l ,:olllJ ht, c"ncluded. 1l0wevt'r. th.· exr.'ns., 3nJ eff,'rt ,· ... mmittt·,t t.l 1II",tt'l tt.':ctin~ rlus the ev .. r pre-sent unct'rt.1inty b:m.1 l.tu., 1.1r,~.·lv t" un.lv,'i.13~lt' b"dv p.ln.'1 !lurf~c~ mis31iKnlllents in thl'

I-h.' ';1'."',1 :;h,,"l.1 bl' hi!t"~nlluKh to) ~et ~"lld re~o)luti,'n "n tilt' 1.,.IJ,. !-"i",~ n,·.l:;urt·.1 (.1 fun.:ti"n ,'f th~ b.113nc~ SVS[t.'III).

'Thi~ i'l .1 fllnct i"n "f tht' n".i .. l l~v .. l ,.f J .. t.,i I ;mJ tit .. p.lrt i':-lIl.lr ';Il!o:;l·.llo· win.l tunn.-l .1n.1 .1~t3 rt."ducti"n pr"ct."Jur..·s. C.l1ibr.1tl"1l !!t,',I"l ';lr.· .:urr.. nt ly h .. ing testt!d in a 11 the ma i~lr SUbS':31 .. ~nd full-sc31~ tunn~ls in th.. country (and abroad) •

• .. ===-_.

production vehicle) warrants sa.. further testing. l For instance, since stabiliaed flow attacb.ent is an attribute o~ low drag designs, a .eans of observins local sarface flow behavior is desirable. • Several ..thods exist and each has advantases and disadvantases. Attachin~ rows of soft, flexible yarn tufts is su-ple, inexpensive, easy to photograph and effectively hiShlight. flow instabilities; it does, hovever, aodify the surface detail by its very presence and can consequently affect the absolute level of the data. An alternative is the use of ink drops (or other visible fluids) which, when placed on the surface spread out and indicate the path of the stre.. lines on the vehicle surface with very little flow interference; the disadvantages of the technique are its transient nature, gravity effects as the droplet spreads along the body side and the ..ss. Seeding the airflow with s.oke or particulates is another approach. Thi~ usually has aany tunnel operation~l considerations which ..y prove unsatisfactory. Often, the ink drop approach is preferred on clay models since tuft attachment aay be difficult. Flow s~paration and instahilities are easily identified. With a 'co.bination of engin.... ring jud~nt 3nd srti!ltic styl~, the d3y surface is iteratively 31t~red in order to d~velop ~ smooth, stabl~ flow pattern. ~t is extrelllt'ly imp"rtant to doculIIo!nt ~ach alteration with pi.:tures. m.. sstlrt'lIIo!nts 3nd templates, ss it is oft~n neces~llry to return to an intel'1llt'd i3te con figurat ion be fore cont inued progress can ~e mad... Front underbody air dams (chin spoil .. rs) snd rear deck spoilers (lips) can often proviJ .. b~neficial results if properly de~igned and locsted (R .. ferenc~s 3-8 and 3-Q). A good c~ndidate devi.:e should be eff.. ctive through a reas"nable range of yaw 3ngl .. s. Ord~ data should be continuously monitor~d in order to help guide the process. tf, after repeated attempts, large areas of flow separation still pxist, .... j"r model contour or shape modifications may be neC .. SS3rv. tf the flow is everyWhere stabilized snd the rear Sep,'Ir3t i,'n point is such that the wake size is minimized, further significant drsg reduction i~ unlikely. Pressure taps may be in"t,11 ... t in the surface of th,- m"del in ,'rder tc.' optimlilly 10c.1te the inl.-tll and ,-xitll for interior ventilo1tion. tf high-mass flow r3m .,ir is r~quired f"r mot-H' or .. n!tine (hybrid) cooling, it ,""uld be wise t,l .::,lnstru.:t " m,'del with properly !lcaled internal flow path ducts. ~ot only is ther~ a Jr3g compon .. nt 3ssoci3ted with the internal flow losses. ~ut the condition ma~ significantly alter the flow over the out~r surf3c~ "f the ve~icle as well.

r.ittle 1lI,'r .. C3n be .1cc01IIplished in m"del sC.11e. Owing t., local Rt.'vn,' I,t~ number. lIcoll.. fi,le Ii t~ .1nd flow cond i t ions, the abs" lute Jr:l~ l~v~ 1" ",-:I Stl r,-,I ill t,-~t IIr .. r.1rely "libstant iated in fu II-s';31!! te~t~ "n t't.- prototvp,' ,'r pr"ducti"n vehi.;le; ful1-sc.1le test re"ult~ 3re "ften 10 to ~O~ ~r~3ter (Reference 3-10). thus contributing to a rath~r IJrg~ un.:~rt3illty ev .. n 3t this p~int. Exp ... rit.'nct.' JnJ .:,~rrelo1tions from previous "ubscale and full-scale tests in the S

l",-c.1u:;e llI,l.t .. l inst,11lat i,'n 3nd setup is not a trivial matter. ttlnn.-l te:; t tim.. is lI:;U:ll1y cont rac teJ for a 6-8 hr !Din imum.

,0 oj _, c -.. ----~. - ---_. -----.-----.------.-.--~- ..

facilitiea can reduce the uncertainty to about +5%. Aa an ultu.ate atep, aerodyna.ic tuniaa on a full-acal. replica ..y be conaidered. The expena. involved in buildiaa a alaal.-purpoa. viDd tunn.1 .ad.1 .., not be warranted; however, a full-.cale IIOCk-up or ..1. back .i&bt be .uitably altered for te.t purpo.... To aak. that .t.p worth.... U_ • • pecial attention .hould be paid to the und.rbody and internal flow detaib.

D. COHCLUDIRG ll!IWUCS

This process should not be considered to be a .indle.. for.ula for success. Rather, it is a fr... vork upon which the des ian development is built. The procedures are hiahly dependent upon ..ny subjective determinations which rely heavily upon ca..on aenae and experience. There may be many alternative solutions to the aa.e set of design requirements.

The objective behind the creation of the deaian auide i. to encourage EHV de~igners to address aerodynamic draa as an important design parameterl ; and once goals are targeted, to systematically evolve a design which is aerodynamically matched to the anticipated mission while minimizing unnecessary effort.

iUntilee high-speed sports and competltlon vehicles which rely h~avil~ on aerodynamic forces for such things as traction and stability, the conventional road vehicle is primarily concerned with the drag component. This is not the say that the other five aerodynamic components are not of interest, but unless unusual operational conditions are anticipated, low drag optimization is usua lly pursued without compromise.

14 SECTIOR IV RU!llERCES

1-1. Hi11iken, V. F., Aerodynaaie Research Plan for Auta.otive-!ype Vehicles, prepared for the Society of Auta.otive Enaineer., Inc •• Oct. 1977. 2-1. Xurtz, Donald V., Aerodynaaie Characteristic. of Sixteen Electric, Hybrid, and Subeo!paet Vehicle. - Coaplete Data, JPL ~ublieation 79-59, June 1978. I 3-1. White, R. C. S., A Method of Bsti.atins Automobile Dras Coefficients, SA! Paper Ro. 690189, Detroit, HI, Jan. 1979. 3-2. Pershing, B., and Hasaki, H., Estimation of Vehicle Aerodynaaic Drag, EPA-46013-76-025 Aerospace Corporation, 1976.

3-3. Smalley, tl. M., and Lee, V. B., Assessment of an Empirical Technique for Estimating Vehicle Aerodynaaic Drag froa Vehicle ~hape Parameters, ATR-78 (7623-03)-1, Aerospace Corporation, July 1978.

3-4. "fucho, tI. H., ''The Aerodynamic Drag of Cars. - Current Understanding, Unresolved Prob1.as and Future Prospects", Aerodynamic Drag ~echanisms of Bluff Bodies and Road Vehicles, General Motors Symposium, Detroit, MI, Sept. 1976. 3-5. Morelli, A., Fioravanti, L., and Cogotti. A., The Bodv Shape of Minimum Ora!, SAE Paper No. 760l86, Detroit, Feb. 1976.

3-6. ~owman, WilliaM D., Ceneralizations on the Aerodvnamic Characteristics of Sedan Tvpe Automobile Bodies, SAE Paper No. 660389, Detroit, Jan. 1966.

3-7. Dayman, Bain, Jr., Realistic Effects of Winds on the Aerodvnaaic Resi~tance ~f Automobiles, SAE Paper No. 780337, Detroit, Feb. 1978.

3-3. Marte, J. F.., Weaver, R. W., Kurtz, D. W., and Dayman, B., A StudY ~f Aut~mobile Aer~dvnamic Drag, DOT-TSC-OST-75-28, Sept. 1975.

3-9. ~chenkel, F. K., The Origins of Drag and Lift Reductions on Automobiles with Front and Rear Spoilers, SA! Paper No. 770389, Feb. 1917.

3-10. Kurt:. Oonald W., The Development of a Low-Drag Bodv Shape for the ~V-l ~le~tric Vehicle, JPL 5030-438, Dec. 1979.

15 ·~------.----.~.,.....-.~

B-1. Eleaperer, w., ''Luftvidentand.unter.ucbun,en an Auto.obil.odellen," Zeit.chrift r. rlu,t.cbnik und Motorluft.chiffahrt 13 (1922), s. 201-206. B-2. Autoveek, May 26, 1978.

B-3. Eodf, W.H., The Aerod~ic DedI! of th. Goldenrod-to Increa.e Stability, Tract10n and Speed, SAl Paper Ro. 660390.

B-4. Itelly, It.B., and HolcoUe, H.J., Aerodrn_ic. for Body !nlineer., SA! Paper Ro. 649A, Jan. 1963. B-5. Paish, H.G., and Stapleford, W.R., A Study to !!prove the Aerodynamici of Vehicle Coolin, Sy.te.l, KIRA Report 1968/4, Dec. 1967. B-6. Emmenthal, It.D., and Hucho, W.H., A Rational Approach to Automotive Radiator SYlt... Delign, SA! Paper No. 740088, Feb. 1974. B-7. Olsen, M.E., Aerodynamic Effects of Front End Design on Automobile Engine cooling System, SA! Paper No. 670188, Feb. 1976. C-l. Cornish, J.J., and Fortson, C.B., Aerodynamic Drag Characteristics of Forty-Eight Auta.obilel, Hiss. St. Aerophysici Dept. Res. Note No. 23, June 1964. C-2. Fluid Dynamic Drag, Hoerner, Sighard F., published by the author, 1958. C-3. Ohtani, K., et al., Nissan Full-Scale Wind Tunnel--Its Application to Passenger Car Design, SA! Paper No. 720100, Detroit, HI, 1972. C-4. Carr, G.W., Reducing Fuel Consumption by Heans of Aerodynamic "Add-on" Devices, SA! Paper No. 760187, Detroit, HI, 1976. C-5. Korff, W.H., The Body Engineer's Role in Automotive Aerodynamics, SA! Paper No. 649B, Automotive !ngineer~ng Congress, Jan. 1963.

lt n-l. "Body Shaping You Don't See , Design News, Hay 5, 1980. E-l. Barth, R., "Effect of UnsyaDetrical Wind Incidence on Aerodynamic Forces Acting on Vehicle Hodels and Similar Bodies" • (report abstracted from. 1958 Stuttgart thesis), A.T.Z., Har. and Apr. 1960, pp. 89-95, HIRA Translation 15/60.

16 U fJEi _ ,0;. t C, •.4!. ? .Z._ ". t .. '~_.' •. ,II -. ~*_ t.~ i I I SECTIOM V L,. IlBLIOCIAPHY

Over 160 report., paper. and book. on variou •••pect. of autoaotive aerod,naaic de.ian are oralni.ed into the followina categorie'l General Autoaotive Aerodynamic. 'acility Teltina Road Teltina Wind Moise Ventilation and Enaine Coolina Stability and Handling General Book. and Proceed ina.

A. CENERAL AUTOHOTIVE AERODYNAHICS Barth, It., "Effect of Unsyaaetrical Wind Incidence on Aerodynamic Forces Acting on Vehicle Hodels and Similar Bodiel" (report abltracted from lq58 Stuttgart thesis), A.T.Z., Har. and Apr. 1960, pp. 89-95, MIRA Translation 15/60.

Barth, R., "Effect of Shape and Airflow about an Automobile on Drag, Lift, and Direction Control," VID, Vol. 98, No. 22, p. 1265 (in German), Aug. 1, 1956. --

Bettes, "l.H., "Aerodynamic Testing of High-Performance Land-Borne Vehicles - A Critical Review" in AIM SymposiUIII on the Aerodynamics of Sports and Competition Automobiles, Los Angeles, CA, Apr. 1968.

Bez, U., Hessung des Luftwinderstandes von Kraftfahrzeugen durch Auslaufversuche, Research report, Dipl. Engr. Thesis, Tech. Univ. at Stuttgart, and Porsche Research Rept., Jan. 1972.

Bowman, W.O., "The Present Status of Automobile Aerodynamics in Automobile Engineering & Development," AIM Symposium on the Aerodynamics of Sports and Competition Automobiles, Los Angeles, CA, Apr. 1965.

Bowman, W.O., "Ceneralizations on the Aerodynamic Characteristics of Sedan-Type Automobile Bodies," SA! Preprint 660389, June 6-10, 1966, ~A~ Transactions, June 1967.

Royce, T.R., and Lobb, P.J. (U.K.>, "An Investigation of the Aerodynamics of Current Croup 6 Sport Car Designs," 'Advances in Road Vehicle Aerodynamics' 1973, pp. 127-145, ~RHRA Fluid Engineering, 1973. Buckley, B. Shaw, Laitone, Edmund V., Airflow Beneath an Automobile, ~AF. Paper No. 741Q28, Oct. 1974.

17 4 4

Burst, H.!., and Srock, Lainer, The Porsche 924 Body - Main Develop!ent Objectives, SA! Paper No. 770311, Detroit, MI, 1977. Carr, C.V., The Aerodynamics of Basic Shapes for Road Vehicles, Part 2t Saloon Car Bodies, MIRA Rept. No. 1968/69. Carr, C.V., The Aerod namics of Basic Sha Part It Simple Rectangular Bodies, MIRA Rept. Carr, C.V., Correlation of Aerodynamic Porce Measurements in Quarter-and Pull-Scale Wind Tunnels (Second Report), MIRA Kept. 1967/1. Carr, C.W., The Development of a Low Drag Body Shape for a Small Saloon Car, MIRA Bulletin No.2, pp. 8-14, 1965.

of Modifications to a ical Car

of Underbod Details on a Tical Car

Carr, C.W., Reducing Fuel Consumption by Me.ns of Aerodynamic 'Add-on Devices', SAE Paper No. 760187, Feb. 1976.

Chou1et, R., Favero, J.L., and Romani, L., "A Study of the Aerodynamic tnteraction Between a Lorry and a Car," Advances in Road Vehicle Aerodynamics 1973, pp. 255-270, BHRA Fluid Engineering, 1973. Cornish, J.J. ttl, "Some Aerodynamic Characteristics of Land V~hic1es," in AtAA Symposium on the Aerodynamics of Sports and Competition Automobiles, Los Angeles, ~A, Apr. 1968. Cornish, J.J., Some Considerations of Automobile Lift and Drag, SAE Paper 9488, Jan. 11-15, 1965.

Cornish, J.J., and Fortson, C.B., Aerodynamic Drag Characteristics of Forty-Eight Automobiles, Miss. St. Aerophysics Dept. Res. Note No. 23, June 1964. l.'°rackre1l, J.F.., and Harvey, J.K. (tmp. Col., U.K.), "The Flow Field and Pressure Distribution of an tso1ated Road Wheel", 'Advances in Road Vehicle Aerodynamics' 1973, pp. 155-168, BHRA Fluid Engineering, 1973.

Flynn, H., 3nd Kyropou10s, P., Truck Aerodynamics, SAE Preprint 284A, 191;t.

Fogg, A., and 3rown, J.S., Some Ex eriments on Scale-Model Vehicles with Particular Reference to Dust Entry, MIRA Report No. 1948 1.

Fosberry, R.A.C., The Aerodynamics of Road Vehicles - A Survey of the Published Literature, MIRA Report 1958/1, p. 25. Fugerson, W.T., "Aerodynamic Drag," Road and Track, pp. 92-98, Mar. 1966.

18 Crotewohl, A., "Seitenwindunterluchunlen an Personenwalen ("Inveltisatins the Effeetl of Crall Windl on ' ....nl.r V.hie1.... ) '.rt 1, A.T.Z., Vol. 69, No. 11, pp. 377-381, KIRA Tr.nal.tion No. \-. 3/68, Hov. 1967. H.wks, R.J., and Sayre (U. of Md.), "Aerodynaaics and Auta.obila Perfo~ance," 'Advance. in Road Vehicle Aerodynaaie.' 1973, pp. 1-13, !BRA Fluid Ensin.erins, 1973. Hawk., R.J., A Tentative Model for Automobile Aerodynamics, KIT, '1966.

Hoerner, S. F., ''rluid-Dynaaic Oral," publi.hed by author (148 BUI teed Dr., Midland Park, NY), 1965. Rogue, J.R., Aerodynamics of Six Passenser Vehicles Obtained from Full Scale Wind Tunnel Tests, SA! Paper No. 800142, Detroit, KI, 1980.

Howell, J.P. (City Univ., U.K.), The Influence of the Proximity of a Large Vehicle on the Aerodynamic Characteristics of a Typical Car," 'Advances in Road Vehicle Aerodynamics' 1973, pp. 207-221, SHRA Fluid Engineering, 1973. Hucho, W.H., Jansen, L.J., and Schwartz, G., The Wind Tunnel's Cround Plane Boundarv Laver - Its Interference with the Flow Underneath Cars, SA! Paper ~o. 750066, Feb. 1975. qucho, W.H., Jansen, L.J., and Emmelmann, H.H., The Optimization of Bodv Details - A ~ethod of Reducing the Aerodynamic Drag of Road vehicl~s, SAE Paper No. 760185, Feb. 1976.

Jansen, t.J., and Hucho, W.H. (Volkswagenwerk AG, Ger. Fed. Republic), "The Effect of Various Parameters on the Aerodynamic Drag of Passenger Cars, I, 'Advances in Vehic le Aerodynamics' 19;3, pp. 223-254, BHRA Fluid gn~ineerin3' 1973. ---- Jansen, L.J., and Emmelmann, H.H., Aerodynamic Improvements - A Great Pot~ntial for Setter Fuel Economy, SAE Paper No. 780~65, Feb. 1978. Kelly, K.B., Kyropou1os, P., and Tanner, W.F., Automobile Aerodvnamics, SAE Preprint ~o. 148B, SAE ~ationa1 Automobile ~eeting, Detroit, ~I, ~ar. 1969.

Kirsch, J.~., Garth, S.H., and Settes, W., Drag Reduction of 31uff Vehicles with Airvanes, SAE Paper ~o. 730686, 1973.

Klemperer. ".l •• "Investigations of the Aerodynamics of Automobiles," !eitschrift fuel' Flustechnik, Vol. 13, p. 201 (in G~rman), 1922.

K"eni~-Fachsenfeld. R., "Aerodynamics of Motor Vehicles," Motor ~undschau Verlas, Frankfurt A.M. (in German), 1951.

!{orff, :l.H., The Bodv Ensineer's Role in Automotive Aerodvnamics, SAE Paper ~o. 64QB, Jan. 1963.

19

• q:; F. ----- 4 • & 6 : .4. f .S',. '414. II 4A# c¥;Ala;t4'.";~S:C:S:YAe;J$5.Q$. __ ~a 44

Kosier, T.D., and McConnell, V.A., "What the Custoael" Gets" SA! Symposium: Where Does All the Power Co?, SA! No. 783, June 1956.

Kuchemann, D.~ and Weber, J., "Aerodynamics of Propuhion," McCraw-Hill Publications in Aeronautical Science. Kurtz, D.W., Aerodynamic Resistance Reduction of Electric and Hybrid Vehicles - A Progress Report, September 1978, HCP/MS03D-274 (NTIS), A~r. 1979. Kurtz, D.W., Aerodynamic Characteristics of Sixteen Electric, Hybrid and Subcompact Vehicles - Complete Data, DOE/JFL/1S2170, June 1979. Kurtz, D.tl., The Deve10 ent of for the ETV-1 Electric Vehicle - Results from W1nd Tunnel !!!!!, JPL 5030-438, Dec. 1979. Kurtz, D.W., A Systems Approach to EHV Aerodynamic Design, Conference Proceedin~s. EV Expo 'SO, Electric Vehicle Council, St. Louis, ~O. Hay lllaO.

,yropoulos, P •• Kelly, K.n •• and Tanner, W.F., Automotive Aerodvnamics. SA! Paper No. Spo-1SO, Mar. 1960.

Lamar. P., "Aerodynamics and the Group Seven Ra.:ing Car," in AIM ~vmDosium on the Aerodvnamics of Sports and Competition Automobiles, Los Angeles. CA, Apr. 1968.

Larrabee. E.E •• Road Vehicle Aerodynamics or Aerodvnamics as an Annoyance, seminar paper presented at the Cranfield Institute of Technolo~y, June 1973.

' • .1;.'. '..z.E., "Is 50 ~itell per Callon Possible with Correct ~treamlinin~?" SAE Jaurnal. Vol. 32, p. 144, 1931.

Lind, !"alter. G.!., "Car Aerodynamics," Automobile Engineer, June 1958.

LJbb, ?J., The AerndYn~mic Effects an Group VI Racing Cars. ~.Sc. thesis, Imperial Cal lege of Science, London University, 1~7l.

~air, !-l.A., "Reduction of Sase-Drag by Boat-Tailed Afterbodies in !.~w-5pe-ad Fl"w," .\eronauti.:al Quarterly, Nay. 1969.

~arcell, R.?, and !tomberg, C.F., "The Aerodynamic Development "f the Char_~er i)aytona for St.Jck Car Competition," Paper 70036, SA! AutJmotiYe !n~r. C~ngress, Detroit, ~I, Jart. 1970.

~arte, J.!., et .11., A StudY of Automobile Aerodv~aMic Drag, DOT-TSC-(IST-75-28, Sept. 1975.

~atthews, S.A., Aerodvnamic Studies Affectin3 ~ar Performance and Aooearance, Ford ~otor Co. of England, Apr. 1962.

~cLean, 1.F., and 5chilli:'lg, !t., "Sehind the Firebird Car's ~ew took," SAE Journal, Vol. 52. p. ~O, Aug. 1954.

20

• ~ ,.' -'-::._'_: .. 0._ .. __ ..------, ;

Milliken, Willi.. , and Zlotnick, Hartin, Aerodyn.. ics of load Vehicle., AIAA Paper Mo. 79-0531, Wa.hinston, DC, reb. 1979. , ; " MoUer, B., "DTal Mea.ure.ent. on the W Delivery Truck, "!'!:!, Vol. 53, 10. 6, p. 153, June 1951.

Morel, T., Aerodyn.. ic Dral of Bluff Body Shape. Characteristic of Ratch-Back Car., SA! Paper No. 780267, reb. ~978.

MoreUi, A., "Aerodynamic Action on an Automobile Wheel," S~POSiU8 on Road Vehicle Aerodyn ..icl, Paper No. S, The City Unlve~.ity, 1969.

Morelli, A., "Theoretical Method for Det.mining the Lift Distribution on a Vehicle," F.I.S.I.T.A., 1964 .•

Morelli, A., Fioravanti, L., and Cogotti, A., The Body Shape of Minimum Drag, SA! Paper No. 760186, Feb. 1976.

Ned1e~, Lloyd, An Effective Aerodynamic Program in the Design of a New £!!, SAE Paper No. 790724, June 1979. Pershing, B. (Aerospace Corp.), "The Influence of Exter!lal Aerodynamics on Automotive System Design," 'Advances in Road Vehicle Aerodynamics', pp. 25-52, BHRA Fluid Engineering, 1973.

~ershing, Bernard, and Masaki, Mamoru, Estimation of Vehicle Aerodvnamic Oras, EPA-46/3-76-025, Oct. 1976.

Porter, F.C., Design for Fuel Economy--The New GM Front Drive Cars, SAE Paper No. 790721, June 1979.

Hchie, D., "Beat the Built-In Head Wind," r:ommercia1 r.ar Journ., Sept. lq73.

Richi

" Rom',1n i. L., "La ~esllre sur pis te de 1.1 Res is tance a L' avancement ," Road Vehicle Aer.ld ... namics: Proc. First Symp., Paper 15,12 pss, City University, London, Nov. 6-7, 1969.

q"mber~, G.F., Chianese, F., Jr., and Lajoie, R.C., "Aerodynamics of Race Cars i:t Draf::ing and ?assing Situations," Paper 710213, SAE Automotive Engineering Congress, Detroit, MI, Jan~ 1971.

~a1t:man, E.J •• .lnd Meyer, R.R., Jr., Drag Reduction Obtained bv Rounding Vertical Corners on a Box-Shaped Ground Vehicle, NASA TM X-S602J, Mar. 1974.

SaLt=man, ~.J •• ~eyer, R.R., Jr., and Lux, D.P., Drag Reductions Obtained bv ~fod i:vin~ a Box-Shaped Ground Vehicle, NASA r.i X-56027, Oct. LQ7':'.

21

• r'" ".", 1'" '1 •

Schenkel, F.~., The Ori,in. of Draa and Lift Reduction. on Automobiles with F~ont and Rear S2011er., SA! Paper No. 770389, reb. 1977.

~chlicting, R., Aerodynamic Problem. of Motor Cars, AGARD Report, 307, Oct. 1960. Schmid, C., "Air Res hunce of Aut01llObUes," Technical University Stuttgart, ~, Sept. 1938. Schmid, C., "Lufwiderstand an Kraftfahrzeugen Venuche _ rahrzeug und Modell," VOl - Verlag, 1938 • . - Scibor-Ryls\Ci, A., (City Univ., U.K.), "Experimental Investigation of the Negative Aerodyn_ic Lift Wings Used on Racing Cars," 'Advances in Road Vehicle Aerodynamics' 1973, p. 147-154, BHRA Fluid Ensineering, 1973. Shapiro, A., Shape and Flow - The Fluid Dynamics of Drag, Science Study Series, Anchor Books~ Doubleday and Co. Smalley, W.M., and Lee, W.B., Assessment of an Empirical Technique for Estimating Vehicle Aerodynamic Drag from Vehicle. Shape Parameters", Aerospace Rept. No. ATR-7S (7623-03)-1, July 1978. Stafford, L.C. (City Univ., U.K.), "A Numerical Method for the Calculation of Flow Around a Motor Vehicle," 'Advances in Road Vehicle Aerodynamics' 1973, p. 167-183, BRRA Fluid Engineering, 1973. Stapleford, W.R., and Carr, C.W., Aerodynamic Characteristics of Exposed Rotating Wheels, MIRA Report ~!o. 1970/2.

~enntswood, D.M., and Craetzel, H.A., Minimum Road Load for Electric ~, SAE Paper No. 670177, Detreit, MI, Jan. 1967. Tustin, R.C., an,dCarr, C.W., Aerodynamics of Basic Shaoes for Small 5aloon Cars, MIRA ~ept. No. 1965/7.

l"·.1,;::in, ?.C' •• ".,ct Carr, C.W., Aerodynamics of Basic Shapes for Small Saloon Cars, MIRA Rept. 1963/10, p. 23.

Yoshiyvki, K., et al., Datsun 280 ~~ - Integration of Aerodvnamics and ADpearance, SAE Paper No.·800l4l, Detroit", MI, 1980.

3. FACILITY TESTINC • r ! Antonucci, C., Ceronetti, C., and-Costelli. A., Aerodvn~mic and Climatic !-lind Tunnels in the Fiat Research Center, SAE· Paper No. 77039~t Feb. 1977.

22 Beauvais, F.R., Trigaor, S.C., and Turner, T.R., "Accuracy of car Wind Tunnel Tests Rot Aided by Hoving Ground Plane," SAE Journ., Vol. 77, Ro. 9, pp. 64-67, 1969.

Beauvais, P.R., Turner, T.R., and Tignor, S.C., "Problem. of Ground S~lation in Auta.obile Aerodynaaics," SA! Paper Ro. 680121, Jan. 1968.

Bettes, W.B., "Aerodynamic Testing of Bigh Performance Land-Born Vehicles - A Critical Reviev," in AIAA SJ!PDsiUD on the Aerodya!!ics of Sports and Competition Auto.obiles, Los Angeles, CA, Apr. 1968.

Bettes, W.B., and Kelly, K.B., "The Influence of Wind Tunnel Solid Boundaries on Automotive Test Data," 'Advances in Road Vehicle Aerodynamics' 1973, p. 271-290, BURA Fluid Engineering, 1973.

Brown, G.J., and Seeman, G.R., The Bighway Aerodynamic Test Facility, AIAA Paper 72-1000, Sept. 1972, also 'Advances in Motor Vehicle Aerodynamics', 1973, pp.323-333, BURA Fluid Engineering, 1973.

3uchheim, R., et al., Comparison Tests Between Kajor European Automotive Wind Tunnels, SAE P~er No. 800140, Detroit, MI, 1980.

Carr, G.W., Aerodynamic Effects of Underbody Details on a Typical Car Model, MIRA Rept. No. 1965/7.

Carr, G.W., The MIRA Quarter-Scale Wind Tunnel, MIRA Report No. 1961/11.

Carr, G.W., Correlation of Pressure Measurements in Model - and Full-Scale folind Tunnels and on the Road, SAE Paper No. 750065, Feb. 1975.

Cogotti, A., et al., Comparison Tests Between Some Full-Scale European Automotive Wind Tunnels - Pininfarina Reference Car, SAE Paper N~. 800139, Detroit, MI, 1980.

Doberenz, M.E., and Selberg, B.P., A Parametric Investigation of the Validitv of 1/25 Scale Automobile Aerodynamic Testing, SAE Paper No. 760189, Feb. 1976.

Fosberry, R.A.C., White, R.G.S., and Carr, G.W., A British Automotive ~ind Tunnel rnstallation and Its Application, SAE Paper 9~8C, Jan. Ll-15, 1965. rasberry, R.A.C., and ~ite, R.G.S., A 250 hp Chassis Synamometer, ~I~ Rept. No. 1963/9. • rosberry, 1.A.C., and ~ite, R.G.S., The MIRA Full-Scale Wind Tunnel, ~IRA Rept. No. 1961/8.

~osberry, R.A.C.'. lind ~ihite, R.G.S., A Wind Tunnel for Full-Scale ~otorVehicles - Oesign Investigation with 1124 Scale Model, MIRA Rept. 1960/2, 24 p.

23 Cross, D.S., and Sekscienski, ".S., Some Problems Concerning "ind Tunnel Testing of Automotive Vehicles, SAE Paper 660385, 1966.

Rensel, R."., Rectangular-"ind Tunnel Blocking Corrections Using the , Velocity-Ratio Method, TN2372, NACA, June 1951.

~, W., and Schmid, C., Automobile Testing, Julius Sp~ing, Berlin, 1938.

lessler, J.C., and "allis, S.B., Aerodynamic Test Techniques, SA! Detroit Section Jr. Activity, No. 660464, Feb. 1966.

~arrabee, E.E., Small Scale Research in Automobile Aerodynamics, SA! Preprint 660384, June 1966. Mason, !-l.T., and Sovran, C. (C.M), "Cround-Plane Effects on the Aerodvnamic Characteristics of Automobile Models - An Examination of Wind Tunnel Test Techniques," 'Advances in Motor Vehicle Aerodynamics' 1973, pp. 291-309, SHRA Fluid Engineering, 1973.

~ason, W.T., and Sovran, C., Cround Plane Effects on VehiCle Testing, G~neral Motors Research Publication GMR-1378.

~et%, L.D •• and Sensenbrenner, K. (Univ. of Ill.)(N.A.R. Corp.), The Influence of ~oushness Elem~nts on Laminar to Turbulent 30undary ta;er Transition as Applied to Scale Model Testing of Automobiles, SAE Paper 730233.

~oLler, E •• ''llind Tunn~l ~feasurements on AutC'tDobiles 1n a Cross Wind," ~. Vol. 53, No.4, p. 74 (in German), Apr. 1951.

~oreLli, A. (Italy), "The New Pininfarino ~ind Tunnel for Full-Scale Automobile Testing." Advances in Road Vehicle AerodynaCli~s. 1973.

~uto, Shinri, and .\shihan, TOUIo-o, The J.A.R.t. Full-Scale Wind Tunnel, SAE Paper No. 780336, Feb. 1978.

Oda, Norihiko, and Hoshino. Teruo, Three Dimensional Airflow Visuali=ation bv Smoke Tunnel. SA! Paper No. 7~l029, Oct. 1974.

Ohtani, K., Takei. ~ •• and Sakamoto, H., Nissan Full-Scale Wind Tunnel - Its ApDlication to Passenger Car Design, SAE Preprint ;20100, '\utomotlve Engineering Congress. Detroit, MI, Jan. 10-14, 1972.

Sykes. D.~. (City Univ., U.K.). "Blockage Corrections for L3r~e Bluff Bod ies in Wind Tunne Is." Advances in ~otor Veh iele Aerodvna:mi.:s, 1973.

Turn~r, T.a., Wind Tunn~l Investisations of a 3/8 Scal~ Automobile ~odel over a ~ovin8-Belt Ground Plane, NASA Tech. Note ~ D-~229. ~ov. lQ67.

Turner. T.R •• .\ ~ovin~-Belt Ground Plane for ~ind-Tunnel Ground Simulation and Results for TWo Jet-Flap Configuration, ~ASA TN 0-4228. 1967.

24 C. ROAD TESTINC

Fuel Econom Measur ...nt - Road Te.t Procedure, SA! J1081 (SA! Recoaaended Practice - Apr. 1974 • Brennand, J., Electric Vehicle Tire and Aerodya.. ic Friction, Road Pover, and Motor-Driveline Efficiency froa-Track Te.ts, SA! Paper No. 780118, Feb. 1978.

Buckley, B.S., Road Test Aerodrn.. ic tnstruaentation, SA! Paper No. 741030, Oct. 1974.

Ya.in, T.P., The Analytical Basis of Automobile Coa.tdovn Testins, SA! Paper No. 780334, Feb. li78. A Digital Technique for the Mea.urement of Total Ora, Deceleration of a Vehicle, MIRA Bulletin No.1, pp. 1410, 1959. Carr, C.W., and Rose, J.J., Correlation of Full-Scale Wind Tunnel and Road Measurements of Aerodynamic Dras, HIRA Rept. No. 1964/5. Cray, R.A., Digital Acceleration Equipment, HIRA Bulletin No.1, pp. 11-14, 1CJ63.

Dayman, B., Jr., Tire Rolling Resistance Heasureaents Frem Coast-Down ~, SA! Paper No. 760153, Feb. 1976. Fosberry, R.A.:., and Holubecki, Z., The Aerodynamics of Road Vehicles - Road Heasurements of Drag and Comparison with Wind Tunnel Measurements, MIRA Kept. 1958/10, II p.

Fosberry, R.A.C., and White, R.G.S., The Aerodznamics of Road Vehicles - A Comparison of Cars and Their ~odels in Wind Tunnels, MIRA Rept. 1958/9, 37 p.

Hoerner, 5.F., "Detemination de la Resistance Aerodynaaique des Vehicules par la Hethode Roue t.ibre," (Determinatioln of the Aerodynamic Resistance of Vehi.:les by the Coastdown Method), ~ 79 No. 34, pp. 1028-33, Aug. 1935. Klein, R.H., and Jex, H.R., Deyelopment and Calibration of an Aerodynamic Disturbance Test Facilitv, SAE Paper No. 8001~3, Detroit, ~I, lCJSO.

I(orst, lI.it., :md White, R.A., "Aerodynamic & Rolling Resistances of Vehicles as Obtained from Coast-Down Sxpe~iments," 2nd International Conf. on Vehicle Mechanics,Paris. Sept. 1971. t.arrabee, E.E., "~1easuring Car Drag," Road and Track, Vol. 12, No.6, pp. 14-~S. t.ucas, G.G., and 3ritton, J.D., "Drag Data frOID Deceleration Tests and Speed ~e35urement3 During Vehicle resting," Proc. of the 1st Road 'lehid. AerodYnamics SYmposium, City Univ., t.ondon, Nov. 1969.

25

• ,

Ordorica, K.A., "Vehicle Perfonaance Prediction," SA! Paper 650623, II Kay 1965, and SA! Joum., Vol. 74, Ro. 1, pp. 1Jl-104, Jan. 1966. Iousi1ion, G., Marzin, J., and Bourhis, J. (Peuleot), "eootribution to the Accurate Keasurement of Aerodynaaic Dral by the Deceleration 1 Method," 'Advances in load Vehicle Aerodynaaics' 1973, pp. 53-66, !!!!! t Fluid Engineering, 1973. Saltzman, E.J., and Meyer, 1l.1l., Jr., Drag lleduc:tion Obtained by Rounding Vertical Corners on a Box-Shaped Ground Vehicle, NASA TK X-S6023, Mar. 1974.

Yalston, W.R., Jr., Buckle!, r.T., Jr., and Marks, C.H., ~ Procedures for the Evaluation of Aerodynaaic Drag on Full-Scale Vehicles in Windy Environments, SA! Paper No. 760106, reb. 1976.

Vhite, J.7., New Techniques for Full-Scale Testing, SA! Preprint No. l48E, SA! National Automobile Heetinl, Detroit, KI, Har. 1960.

White, R.A., and Korst, H.H., The Determination of Vehicle Drag Contributions from Coast-Down Tests, SA! Paper 720099, 1972. Also, 'Advances in Road Vehicle Aerodynamics' 1973, pp. 15-23, SHRA Fluid Engineerin" 1973. Schmid, C., "Aerodynamic Drag of Motor Vehicles: Experiments with Full-Scale Car and Model," Deutsche Kraftfahrforschung, No.1, 1938, ~ Verlag (in German). Sherman, D., "Project Car: Crisis-Fighter Z-Car," Car and Driver, May 1974. Sherman, D., "Project Car: Crisis-Fighter Pinto," Car and Driver, Mar. 1974.

~turm, J.M., Acceleration and Fuel Measurements - New Tools and Techniques, SA! Paper 471G, Jan. 1972.

D. WIND NOISE

McDaniel, D.W., Hushing Automobile Noises, SA! Preprint No. 477A, Automotive Engineering Congress, Detroit, Jan. 1972. Richardson, E.J., Isolation and Cure of '..zind N·;ises, SA! Special Publication 195, pp. 14~31, Feb. 1961. Oswald, L.J., and Dolby, D.A., A Technique for Measuring Interior Wind Rush Noise at the Clay Model Stage of Desi3n, SAE Paper No. 770394, Feb. 1977.

lamberg, G.F., and Lajoie, R.G., An Objective Method of Estimating Car Interior Aerodvnamic Noise, SA! Paper No. 770513, Feb. 1977.

Wattanabe, Masaru, Harita, Mituyuki, and Hayashi, Eizo, The Effects of Bodv Shapes on Wind Noise, SA! Paper No. 780266, Feb. 1978.

26

• !. VENTILATION AND !HGIH! COOLING

Davenport, C.J., Beard, R.A., and Scott, P.A.J., Optimization of Vehicle Coolin! Syste.a, SA! Paper No. 740089, Feb. 1974.

~nthal, ~.D., and Rucho, V.R., A Rational Approach~to Auta.otive Radiator Syste.a Design, SAE Paper Ho. 740088, reb. 1974. FO&l, A. and Brown, J.S., Some Experia.nts on Scale-Hodel Vehicles with Particular Reference to Dust Entry, KIRA Report 1948/1.

Goetz, Rans, The Influence of Vind Tunnel Tests on Body Design. Ventilation, and Surface Deposits of Sedans and Sport Cars, SA! Paper No. 710212, Feb. 1971. I Olson, H.E., Aerodynamic Effects of Front End Design on Automobile t Engine Coolin! Systems, SA! Paper No. 760188, reb. 1976.

Paish. M.G., and Stapleford, V.R., "A Rational Approach to the I Aerodynamics of Engine Cooling System Design", 1968-69 Proceedinss of the Institution of Mechanical Engineers, Auto.obile Division, vol. 183, ?art !A, Number 3, England.

Paish, H.G., Airflow Heuurement Through Vehicle Cooling Systems," MIRA Bulletin No.6, 1966.

Paish, M.G. and Stapleford, W.R., A Study to Improve the Aerodvnamics of Vehicle Coolin! SYstems, HIRA Report 1968/4.

Tayl~r, G. I., Air Resistance of a Flat Plate of Verv Porous Material, British Aeronaut. Research Council Rept. and Mem 2236, 1944. Wallis, S.B., Ventilation System Aerodvnamics - A New Design Method, SAE Paper No. 710036, Feb. i971.

F. STABILITY AND HANDLING

Basso, G.L., Functional Derivation of Vehicle Parameters for Dvnamic Studi~s, National Aeronautical Establishment LTI-ST. 47, Ottawa, Canada. Sept. 1974.

Hawks. R.J •• The ~ffect of Aerodvnamic Forces on the Performance and Handlin! Qualities of High-Speed Auto.o~, Ph.D. Dissertation, Univ. of Maryland, Jan. 1972.

Hawks, R.J., and Larrabee, E.E., "The Calculated E:ffect of Cross Wind Gradients on the Disturbance of Auto.obile Vehicles," presented at AlAA SYmposium on the Aerodynamics of Sports and Competition Automobiles, Los Angeles, CA, Apr. 1968. Korff, W.R., "The Aerodynamic Design of the Goldenrod to Increase . Stability. Traction and Speed," presented at AIM Symposium on the Aerodvnamics of Sports and Co.petition Automobiles, Los Angeles, CA, Apr. 1968.

27

• . , ~ ------~ -., -. ~ ..... -~- .,..- ...... ~---~.------,.---~-

Lay, W.!., and Letts, P.W., "Wind Iffects on Car Stability," SA! Transactioas, Vol. 61, p. 608, 1953. ---- II HabiB, J. (Univ. of rla.), ~ariatioa in Vehicle Handliaa Characteristics Under Gusty Condition.," Advance. in load Vehicle Aerodyn&lllics, 1973.

Moncara, H.J., Barlow, J.B., and Ravks, a.J. (Univ. of KD), "StabiUty I and Cro.s-Vind ".pon.e of an Articulated Vehicle vit~ 1011 rreedoa,· i Advance. in Road Vehicle Aerodyn&lllics, 1973. Weir, P.H., Heffley, R.~., and ainlland, a.r., "Si.ulation Investisation of Driver/Vehicle Performance in a Hishvay Cust ~ Environment," 8th Annual Conference on Manual Control, Kay 1972.

C. GENERAL BOO~S AND PROCEEDINGS Vehicle Dynamics Terminology, SA! J67d, SA! Sandbook Supplesent J671, published 1965. Bekker, M.C., Theorv of Land Locomotion, University of Michigan Press, Ann Arbor, MI, 1956. Bussien, R. (editor), Automobiltechnisches Handbuch, Technischer Verlag, Herbert Cram, Berlin, 1942. Hayes, K.R., and Bannister, B., Auto Union Audi Saloon Car, KIRA Rept. No. V.A. 21, 21 p., 1963. Kamm, W., Das Kraftfahrzeug (The Kotor Vehicle). Whitelaw, R.L., ''Three Iaperatives in the Autoaobile Future," ProceedinRs of the Second International Conf. on Vehicle Mechani'!s, Paris VI University, Sept. 1971. Aerodynamic Drag Mechanisms of Bluff Bodies and Road Vehicles. GM Symposium, Sept. 1976, edited by Gino Sovran, Thomas Korel, and ~illiam Rason. Plenum Press, 1978. Aerodvnamics of Sports and Competition Automobiles, edited by Bernard Pershing, AIAA Syaposium, Kay 1974. "Aerodynamics of Transportation," edited by Thomas Morel and Charles Dalton, proceedings of ASHE Symposium Held June 1979, Niagara Falls, NY Advances in Road Vehicle Aerodvnamics, 1973, edited by H.S. Stephens, BH~ Fluid Engineerins, 1973.

Automotive Aerodvnamics, SAE/PT-78/16 (selected SAE Papers through 1977) •

"Road-Vehicle-Aerodyn&lllics", edited by Carl Kraaer and Bans J. Cerhardt, Proceedings of the 4th Colloquium on Industrial Aerodynamics, Aachen, W. Ge~ny, June 1980.

28

• ------.---- ...;::--~---...::.:.--:;...;;;-;.;...-~.,;.;..'-'-.-..;;;;.--...;..;;.-...;.-=-.=-----=-==~~~--~------

APPENDIX A

EFFECTS Ol ASPECT RATIO AND llREHESS RATIO OR THE AERODYlWfIC CHARACTERISTICS OF AU'IOKOBlLE SRAP!S

Because of their special battery packaging requir~nts, electric vehicles may not be subject to the same design constraints as conventional IC· engine vehicles. lor instance, owing to the use of a I central battery tunnel, a small vehicle may be unusually vide or long. A series of tests vas therefore performed in the CALC IT 10 foot vind tunnel (Caltech) to determine if aspect ratio or fineness t ratiol was an important aerodynamic parameter, and further, whether one can generalize the effect of either or both in combination for simplified automobile shapes.

These tests were exploratory in nature and intended to deteraine what, if any, trends would appear. The initial tests involved both a sharp-edged and a round-edged basic model (Figures A-I and A-2), in order to quantify the effect of local flow separation on the observed aerodynamic trends.

The parameters varied were height, length, width, and ground clearance; Figure A-3 illustrates the model construction teChnique. Three variations were available for each of the four parameters. Figure A-4 illustrates the drag trends demonstrated by highly sp~arated (sharp-edged model) and highly attached (round-edged model) flew situations at low to moderate fineness ratios. As one might expect, for very short vehicles, the drag is reduced with increasing finpness ratio. This is probably due to a reduction in the form drag component (see Appendix D, Part D) at the expense of a small increase in surface friction drag. Owing to local separation points, the drag gradient is not as large for the sharp-edged model as for the round-edged, but the trend is not significantly different. Subsequent tests involved only the round-edged model.

The effects of ground clearance were found to be significant with these smooth-underbody models (see Figure A-S). This also presents a problem in data presentation since the manner by which the ground clearance is nondimensionalized can distort the effects of aspect and fineness ratios. For instance, if the ground clearance is nondimensionalized by body width and the aspect ratio is varied by . changes in body width (g/W) ground clearance changes with aspect ratio and dominates the whole effect. Similarly, ground clearance nondimensionalized by body length (gIL) will dominate the effects of changes in fineness ratio. For these reasons, two ground clearance parameters, gIL and g/W, are used when evaluating the effects of I aspect and fineness ratios, respectively.

lAspect ratio (AR) is defined as body height (not including ground clearance) divided by width, and fineness ratio (FR) as length divided by effective diameter (of ~quivalent area circle).

29

• Figure A-i. Basic Sharp-Edged Model Mounted in CALCIT Wind Tunnel

Figure A-2. Basic Round-Edged Hodel Mounted in GALCIT Wind Tunnel

30

• ·, .I t I i I

I \

I I I t !

Figure A-3. S~~e of the 56 Pieces Used to Alter Aspect 3Ild Fineness Rat ios

0.64 0.70

ROUND EDGED

I 1 1 1.6 1.8 2.0 2.2 2.4 FINENESS ItATIO

Figure A-4. Drag Coefficient vs. Fineness Ratio for Sharp-Edged and Round-Edged Automobile Shapes (g/W - 0.15. Ground Clearsnce • 15: of Body Width)

31 . f<'

I·

Coo

0.30 1vMFi- 0, 2.2 Q 2.7 t::. 3.2 0.26

10 20 30 GlOUND CLiAIANCE. , OF IOOY WIDTH figure A-5. Drag vs. Ground Clearance (Aspect Ratio • 0.88)

The effect of aspect ratio on drag is shown in Figure A-6 at two levels of ground clearance representative of present day automobiles (gIL • 5%) and vans (gIL • 8%). In both cases, the drag usually increases with aspect ratio (short and wide has some advantages over tall and narrow), being more pronounced at the highest fineness ratio (longest vehicle). For high-ground-clearance vehicles, there seems to be a weak aspect ratio effect up to about AR • 0.8; beyond that point, the drag increases significantly.

The effect of fineness ratio (Figure A-1) is a little more confusing in that the trends with constant aspect ratios are not as internally consistent. Note also, that the two ground clearances representing "automotive (g/W • 10%) and van-like (g/W • 20%)" are nondimensionalized by body width for the reasons explained earlier. tn general, the trend is consistent with Figure A-4 which covered the very low fineness-ratio end of the spectrum. However, as the fineness ratio is increased, significant drag reduction ceases and the drag actually begins to increase beyond a fineness ratio of 2.1 at the higher ground clearance. This may indeed be the result of 3 rapid buildup of the surface friction drag component (see Appendix B, Part 'S), which may be magnified in the underbody region at high ground clearances.

32

• , .~, ..¢ =:s. *;. ,; ..,> s. U, t t

t36 .. SYMI Fil t . 0 2.2 , a 2.7 gil'" Ut I!. U "- "Do i tlZ ~ tlO gl\.'~

0.21

0. 7 Q.8 0.9 ASPECT RAT 10, HtW

Fi~ure A-6. Drag vs. Aspect Ratio at Two Ground Clearances

o.)tr--,,;:------.

g/W - 20'11.

SYM AI o 0.58 IJ 0.10 A 0.11 0••

g/W -I"'" r I 0.26 , . 2.7 3.2 FINENESS IlATlO, I.J1)

rigure A-7. Drag vs. Fineness Ratio at Two Ground Clearances

33 jiiF .. , .• JPS. r-- . i A . P .4 i.!!Q. *.. if'.'*'" , =.. ;x::;::u ==!'

In .u.aary, the.e re.ult.-indicate that there are a.pect and finene •• ratio effect. on vehicle dra, that warrant con.ideration durin, initial de.i,n ~a,e. when pack.,inl requir... nt. are beina developed.

34 Ie 04_ t ttd'L. ai .. C,,',!'. Pi;etc.; .a_f.'i."P, '':;::: .... ,CZ4A'4A4..... lllE14.1.'¥Jtu J .a;(i.dJsqwtU.¢4tt 4.. 2(jUW. , rPi, J ~ t

APPENDIX B FOUNDATIONS or AERODYNAMIC DESIGN •

The purpose of this .ection i. to familiarize the EHV design engineer with certain ba.ic concepts related to aut~otive 'aerodynamics. First, the historical development of the automobile, from an aerodynamic perspective, is briefly reviewed. Next, the generally accepted "sources of drag" are identified, ranked by importance and described by example. Finally, a limited aerodynamic data base, developed by wind tunnel testing 20 electric, hybrid and subcompact vehicles, is presented in order to orient the design en~ineer with the state of the art.

A. HISTO~ICAL DEVELOPHENT

AlthouRh many of the principles involved'in low-drag designs hava ton~ been known, the drag coefficient of the average production car in the early 1920s was-about 0.&. By 1940 it had dropped to about 0.6 and by 1960 to about 0.5 (see Figure B-1). Further improvement h3~ come ~lowly, especially in this country, and the average drag coeffici~nt of domestic autOMobiles actually increased slightly (to 3hout 0.;5) in recent years ,lith the trend toward more formal styling ".ith ll!ss rotln'Hn~ of ed~es. Most recently, however, the pressures brought "y federally mandated fuel economy requirements have sparked renew~d interest in reducing aerodynamic losses. In Europe, the curr~nt avera~e production car drag coefficient is somewhat lower, 3hont 0.411. Drag coefficients as low as 0.15 were reported as early 3,q 1'1'22 hy ~l. 'rt?!lent-dav producfion car drag levels nearly in half may not he cOl'lplt?tp.ly unrealistic.

35 .:

• 51 , 40$ aq, *:< -" .::;1. 5 $.4 , .& ... = t, p .... i au i. W ~ '.oA * ... Q ; = ;w .;a.W 4A.. .6 J ,

LO 0.1

0.6

o.z STREAMlIN£O t;..:=::::::...1- - -l!!9~L_ , ·Q.lS

0.1 . i I 1930 11160 1910 1980 "EAR Figure a-I. Aerodynamic Drag of ':ars as a Function of Time

~. SOURCES OF DRAG

The actual mechanisms of automotive dr6g production are not at all well understood. Automotive aerodynamics is characterized by ~r~und interference and large areas of separated and vortex flow. U'll ike .1ircraft :h.rll-!ynamics it ill largely unrespl\n:live to classical 3'l31ytic31 treatment. It has therefor~ become a rather empirical ~cience, relying heaVily on development thr~ugh wind tunnel test techniques. Reference B-4 and others brea~ down the sources of dr~~ into five basic categori.es: (1) form drag, (2) ir.terference Jrag, (1) iatp.rnal flow drag, (4) surface friction dr4g. and-(S) i~duced Jr3~. A simple schemat~c depicting their relative importance for an Ie engine car is presented in Figure B-2.

; \ /INTERNAll ~ '. flDW' \ ) DRAG SUlfAe!'. !IjDUCE 'fRICTION' OaAG : DRAG

Vigure d-2. Distribution of IC Engine Vehicle Aerodynamic Drag (Reference B-4)

36

• Fora drag (sa.etimes called profile drag) is a function of the basic body shape. Bodies which aini.ize the positive pressure on the nose and the negative pressure on the tail viII exhibit lower fo~ drag. lor exaaple, a flat plate positioned norsal to the flow would • represent a worst case, whereas a streaalined teardrop shape would be characteristic of ainiama fo~ drag.

Interference drag develops as the flow over the many exterior appendages of a vehicle body interacts with the flow over the basic shape or the flow due to the constraining influence of the ground. Various component projections such as a hood orna.ent, windshield wipers, radio antenna, external mirrors, door handles, luggage rack, rain gutters, and underbody. protuberances all contribute to the interference drag component. For example (Reference B-4), an external mirror in a free airstre.. may have a dr~g force of 4 newtons; In close proximity to the vehicle body where the local airflow is accelerated by 25-30%, the drag on the mirror may be 6.4 newtons --a 60% increase! Since an ~~ternal mirror usually has a large flat aft end, it spreads a turbulent wake behind it which disturbs the basic flow on the side of the vehicle, adding a further drag incr~nt. Projecting elements usually cause less interference on high-drag body shapes than on lov-drag bodies. Since a high-drag body is usually characterized by extensive regions of .separated flow, many of these elements are hidden in the already disturbed flow pattern. Conversely, the low drag of an efficient body is the result of ~ high degree of flow attachment. That condition is usually tenuous'and any projection from the surface may cause separation. The underbody projections are some of the pr~e offenders as the installation of a smooth belly pan has demonstrated many tilles (Reference 3-8). In the case of electric vehicles the traditional arguments against using a smooth belly pan--such as ease of maintenance, safety (oil drippings, etc.), and engine cooling restrictions--.ay not apply.

Internal flow drag arises because air is required to move through the vehicle as well as arou~d it. A conventional water-cooled IC engine requires a substantial amount of radiator airflow. Typically, the flow path is highly inefficient as local stagnation areas develop in the engine compartment and the exit path is filled with struts, hoses, brackets, and suspension elements. Here again, an electric vehicle may have an inherent advantage since its cooling requirement may be an order of magnitude less. However, ventilation of the passenger compartment is an important comfort and noise consideration, and care must be taken to design and locate the inlets and exits properly. The conventional approach is to place a flush inlet in a relatively high pressure region (usually at the base of the windshield) and either place exits in a low pressure region around the t rear window or rely on normal body leaks'. Unless a scoop is placed • out in the flow (in which case there is an interference drag component), the drag increment due to noraal occupant ventilation requirements is negligible.

37 Surface friction draa relult. fro. the boundary layer which i. for.ed al air IIOvel alona a .udace. Ovina to vhcou. friction force., the velocity Iradient nor.al to the' .urface Ilv•• ri.e to a .hear layer. Th•• urfac. finilh or ...11 i8Perfection., and the .i.e of the ar.a expo.ed to the flow, deter.ine the level of thi. dral coaponent. Production car finllhe. (.urfac. Irain .i•• of 0.1 to 0.5 ail.) are vell below the critical level where additional .lIOothne •• would reduce the local friction. A .lIOoth, continuou•• urface "ep. Ikin friction low. A. the flow IIOve. rearward alona a body it continually lo.e. energy and .eparation i. IIOr. likely to occur in critical areal. Window fr.... , ,ap', ahaatched part., and "onul Ikin friction all contribute to cau.e a buildup of the boundary layer, leading to leparation, aore turbulence and increaled drag.

Induced draa arilel froa the for.ation of longitudinal trailing vortices Kenerated by the pre.lure differential between the vehicle'. underbody and roof. The energy required to lenerate and .upport thi. vortex field is related to the energy conlumed by induced dral. Often tenaed "Ii ft-induced" drag or drag due to lift, there is now real doubt that any simple relation.hip between lift and induced drag ~xists (Reference ]-4). It can normally be minimized by careful attention to design detail on the rear portions of the vehicle, but this usually requires an experimental ~pproach.

C. AERODYNAMIC DATA BASE

Very little reliable aerodynamic data on conventional automobiles and virtually none on special electric or hybrid vehicle5 is available in the public domain •. The automobile manufacturers, both foreign and domestic, have generated. a great de£l of aerodynamic information for Ie engine vehicles but it remains largely proprietary. Most of the available data is from subscale wind tunnel t.-ts .If questionable or unknown origin. Here lies a basic problem with r~ndom wind tunnel data: it is usually not reliable nor directly compnrable to other test resulto. Owing to such factors as scale, level of detail (internal flow paths, undercarriage, etc.) flow ~onditions, and data reduction pro~edures, the absolute values of the coefficients are of limited value. The difference in measured drag h~twt'.-n :I "reasonably detailed" scale model £nd the full-sized production vehicle is often 20t or greater. The same auto~obile tested in two ,lifferent wind tunnels may yield drag results which differ by lot. The various tunnel wall corrections £lone can modify th ..- .trag by 10:. To lIIaxilllize its usefulness, a data base must be g«"uerated at the sallie model scale, in the same wind tunnel under the 831111' ~onditions. ~nd be handled using identical data reduction procedures. The relative effects r~presented by the data b£se shouid then be sufficiently reliable for design use. Correlatiolls with road test results can help to establish a confidence level for the absolute vslups.

With this hackground in lIIind, it was determined that the developaent of an F.HV aerodynamic data base should be initiated by perfor.ing full-scale tests in the Lockheed-Georgia Low-Speed Wind

38 tunnel. A Reque.t for Quotation (RrQ) va. prepared and .ent to 25 owner. or d.veloper. of electric or hybrid v.hicle. a.kinl for the u.e of a vehicle for aerodyn.. ic characteri•• tion te.tinl durinl a .pecific ti.. period. "ine bid. vere receiv.d before the IIQ clo.inl date. ~nl the .el.ction criteria u.ed ver••

(1) Availability.

(2) Compatibility with wind tunnel balance .y.tem.

(]) Aerodynamic int.rest.

(4) Loan and tr.n.port.tion fees.

Four vehicle. were selected by this proces.. In .ddition, thr.e electric vehicle. were lo.ned by the NASA Lewi. Rftsearch C.nter. One wa •. loaned by South Co.st Technology and three were av.ilable at JPL. To supplement the Iroup, several convention.l lC .ubcomp.cts vere borrowed from local dealership. and individu.l.. In three c •••• , • facsimile of an IC engine/E~V conversion was .ub.tituted.

These vehicles are described in T.ble B-1 .nd shown in Figure B-3. Forty-~ight vehicle configuration. were inve.tigated in the course of the testing to quantify the effect. of .uch thinss a. open winltows, att itude changes (due to loading) and pop-up headlight. (References 2-1 and 3-10 contain more detailed information on this •• vell ao the other aerodynamic force and moment component.). The zero-yaw drag coefficient. of all 20 vehicles in their ".tandard" configllrlltions, their frontal .ueas and drag-area products are also includ~d in Figure B-3. When the yaw characteristic. are con.idered (effect~ of ambient winds), the relative values change slightly (Reference 2-1). See Appendix F.

The vehicles were mounted on the external balance by means of a four-point support sy~tem. No attachment was required; the wheels merel~ rested on the four pads with the parking brakes locked. The friction between the tires and the pads was normally sufficient to maintain model position. In certain cases, chocks were placed behind the tires. Because of the extremely short wheelbase. of .ome of these electric vehicles, it was necessary to use pad extension.. These raised the position of the vehicle in the tunnel by approximately J cent imeters. To quantify the effect of. this position change, tests vere mad~ usinR spacers with a few of the vehicles that were capable of lIsinR tht! unmodified pads. Elevating It vehicle in this manner appearetl to increase the measured drag by 1-2% ovrr the ent ire yaw rllnjtt".

All tests were performed .t 88 kph and the yaw angle (Ib) was varied through +40 degree5. Runs were also made on all vehicles vith the two front windows open. Some tests of Ie engine cars vere run with rll,Hatllu btlth open and blocked.

39 D. OBSERVATIONS It ia difficult to aake univeraal statements about the data • aince, in automotive aerodyn.. ics, broad generalizationa uaually prove to be unreliable. There are many aubtle detaila characteriatic of each vehicle which affect the local flov conditions and hence, the forces and moments. To atate that vehiclea of a particular class all exhibit predictable aerodynamic traits is risky at beat. Nevertheless, certain features characteristic of this data base vill be highlighted in vhat follows. In addition, a simplified procedure for accurately determining the effects of statistically varying ambient vinds on a vehicle's drag is presented (and applied to thia data base) in Appendix F.

It is interesting to note that the selected vehicles represent a range of zero-yaw drag coefficients from 0.308 to 0.583. Further, the highest value (least aerodynamically efficient) of the group was the Kaylor open roadster followed closely by the boxey Otis van; however, the HEVAN drag coefficient was nearly 15% less at 0.497 despite its boxey lines. Another interesting result vas that the Horizon's drag coefficient was over 18% lower than the Chevette's even though they are very similar in shapel • General Electric's ETV-1 and Centennial have drag valves significantly lower than the rest of the group--a probable result of the importance of aerodynamics in the design theme and subscale wind tunnel testing. Windows Open/Closed Because of their current limited energy capacity, electric vehicles will not immediately be able to afford the luxury of an active air conditioning system; it is therefore reasonable to expect that they will be operated in a windows-open configuration over a significant portion of their lifetime. As previously discussed, open windows adversely affect the slope and ultimate magnitude of the drag-yaw curves. Curiously, open windows mayor may not increase the drag at zero-yaw angle. In fact, four vehicles (Honda Civic Sedan and Wagon, HEVAN, and the Chevrolet Corvette) actually had a lower zero-yaw drag with their front windows open than when closed (almost 4% lower on the civic wagon). This situation was previously observed while performing precision coast-down testing on a 1975 Chevrolet tmpa13 (Reference )-8). Although they reported this result, the authors were uncomfortable with it, and desired further investigation. The present data seems to confirm that the circumAtance can and does occur. However, it should be noted that a vehicle operates at some angle of yaw (wind-induced) over most of its

IThe relative drag levels of the cars tested in the Lockheed-Georgia wind tunnel mUdt not be taken as typical of all their manufacturer's products. L 40 ---.. _. __ ._------

lifeti.. , therefore, the effect of open window operation i. a net increa.e in the vehicle'. draa of approx~tely 3 to 5% (depend ina upon the drivinl cycle and wind .peed - .ee Appendix r). Cround Clearance There i. a natural boundary layer (velocity ,radient) aravth alons the wind tunnel floor re.ultins ia a thickne •• of about 15 ea (6 in.) at the te.t .ection aidpoiat for the Lockheed-Georsia wind tunnel. Since .e.. ral of the .hort wheel ba.e vehicle. had to be mounted on rai.ed/cantilevered plate. (approximately 3 ea above the floor), a brief check va ...de to quantify the effect. The Chevette had a wheelba.e lenath which ..de it po •• ible to .aunt it either on the flu.h balance pad. or on the cantilevered plates. Tests were performed in both po.ition. vith all other para.eters unchanged. The effect of rai.ins the vehicle va. to iacrea.e the dras by fro. 1% to 2% over the entire yav range. Certainly, one would expect there to be some increa.e .ince the vehicle i. moving further out into the undisturbed free.treaa flow. It i. believed that the effect observed with the Chevette i. probably typical for the other vehicles tested on the cantilevered plate.. It .hould be noted, however, that the data presented for these vehicle. have not been corrected for this effect. The vehicles are: (1) Ronda Civic Sedan, (2) Honda Civic Wagon, ~~) Ford Fiesta (here the .cunting procedure resulted in unly a 1 1/2 em elevation and the effect i. expected to be less than 1%), (4) CDA Town Car, (S) Sebring-Vanguard Citicar, and (6) the Zagato Elcar. Radiator Airflow It has long been recognized that, for conventional auta.obiles, radiator airflow i. a .. jar .ource of aerodynaaic drag. A great deal of effort has gone into developing designs vhich accomplish the engine cooling task while minimizing the detri.. ntal aerodynamic effects (References B-S, B-6 and B-7). An all-electric vehicle, however, does not have a motor cooling requirement of similar magnitude and therefore should po.ses. an inherent advantage in this respect. tn ~n effort to quantify the benefit, two vehicles (the Chevette and the Corvette) vere tested vith their radiators both open to airflow and blocked. The blocking was accomplish~d by simply covering the grille, and other radiator inlet areas, with flexible sheet plastic held firmly in place vith duct tape; all related body contours remained undisturbed. The Chevette vith an open radiator exhibited about 7-8% higher drag than when the radiator was blocked. This increment was approximately constant aero •• the yaw range, hut the as,..etry was exa~~erated with the open radiator. The Corvette had a 6 1/2% drag increase when open ca.pared to blocked; this ca.parison, however, was made at zero yaw only. It i. anticipated that the radiator drag increment might be different for each vehicle, and had ti.. permitted, this would have been investisated. In su.mary, however, if an IC engine vehicle vere converted to electric pover and the radiator airflow vere eliminated, one could expect a drag benefit of from 5 t~ 10%.

L 41 Tabl. 1-1. Data Ba •• V.hicl••

Figure Vehicle

• Gener.l !lectric Co.: !TV-1 4-p.... nlu electric c~t.r

b Garrett AiRe.earch Co.: ETV-l 4-p••• en su electric co.auter

c General !lectric Co.: 4-p.ssenser electric Centennial Electric cOllllllUter

d Copper Development Association: 2-passenger electric Town Car cOllDuter

e South Coast Technology: 2-passenger electric Electric Rabbit cOlllllluter

f Sebring-Vanguard: Citicar 2-passenger electric cOlllllluter

g Zagato: Elcar 2-passenger electric commuter

h Jet Industries: Electric delivery van Electra-Van 600

i otis Elevator Co.: Otis P-500A Electric delivery van Van

j Kayl~r Energy Products: 2-passenger ~ybrid­ Kaylor CT electric open roadster

k Energy Research and Develop­ Hybrid-electric delivery ment C~rp.: HEV~~ (Hybrid van Electric Van)

1 American Motors cory.: 1973 Internal ':-'IIloustion P3cer Station Wagon engine

m Ameri.::3n Mot~rs Corp. : 1978 Internal c:nDbustion P3cer Sedan engine

n General Motors C"r~. : 1967 Internal combustion Chevrolet C~rvette- engine

0 Gener.]l Mot.)rs C"rp. : rnternal .:~mbusti"n - 1973 Otjsmobile Del:3 8a3 engine

!) Cener.ll Motors C.lrp. : 1973 Internal .:ombusti~n Chevrolet Chevette 4-doot engine

42 .... ----.--.... ~~..--.--,-.---- ... -~---~----- .

! f q Chryalu Corp.t 1978 Pl,.outh taterael coabultioa f RoriaOG 4-door .alia. ! ~ r ROGda Kotorlt 1978 Civic tateraal coabultioa SHan ealia. s Roada Motorll 1978 Civic tateraal coabultioa ValOa ealiae t Ford Motor Co.t 1978 Fi.lta tateraal coabultion .alin.

Table Rotes

IThis production tC 8nline Pacer Valon reprelented a realonable facsLaile of the Electric Vehicle Associates "Chanle of Pace" converted electric Pacer . flagon.

~This production IC engine Corvette represented a realonable facsimile of the Cutler-Hammer Electric '67 Corvette of Santini. The front grille vas blocked in order to eliainate the radiator IOlses, vhich are not present in the electric version.

lrhis productior. IC engine Delta 88 vas a reasonable facsi.ile of the proposed Rational Motors Hybrid-Electric Gemini II. Here the radiator vas , no: blocked since the hybrid vehicle would retain its V-6 engine and cooling system.

43 -~ .. ----- .---,--.. ..-.-.-.~ ... ----- ...... ,._ ..-.--­ -, ,-- -- _._-_ --... --- .. - . . ,. --_. .- ...---- .. -'--'_ .. -' -_

.: ".-',.- '~. .,\ -.

a.

CE ETV-1 2 CD oA, 1Il 1.840 0.567

b.

Garrett ETV-2

CD o 0.395 2.028 0.801

Figure B-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel

44 _____ ,,~~_ ... _____ r ___ - __• ___~

.;

J;

c.

CE Centennial

1.851 0.624 •

d.

COA Town Car

Co o 0.367 1.754 0.644

Figure B-3. Vehicles Tested in the. Lockheed-Georgia Low-Speed Wind Tunnel (Continuation 1)

45 ·._, ...... --- ._------'-'-'-==.- ... ----~--. --~...:":::. ======

e. '.

Set Rabbit

1.821 0.836

f.

Sebring-Vanguard Citicar

A, 1Il2

1.700 0.920

Figure B-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel (Continuation 2)

ORIGINAL PAGE IS 46 OF POOR QUALITY -"-,.----

I·

Zagato Elcar

1.838 0.901

h.

Jet 600 Van

A, ID~

0.539 1.942

Figure B-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel (Continua:ion 3) --.---~------.---.------.~-.~.. ~---~--~-~-~-~~~~~~~~~~~~

i.

Otis Van

0.581 2.593 1.507

j.

Kaylor GT

A, \11 2

0.583 1.359 0.792

Figure B-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel (Continuation 4)

48 k.

Ent>t'gy R&D REVAN ., Co A, m­ o 3.283 1.632

1.

AMC Pacer Wagon

Co A. m-" o 2.225 0.903

Fi~lre 8-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel

49 -.-.~.------== '------_-_-_-__ --_-_--~-----u-·------·-;--~------9

III.

AMC Pacer Sedan

CD o 0.450 2.222 1.000

n.

Chevrolet Corvette

CD o 0.490 1.925 0.943

Figure B-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel (Continuation 6)

50 ------

•

o.

Oldsmobile Delta 88 Sedan ., CD A, 111- o 2.077 1.159

p.

Chevrolet Chevette

1.765 0.886

Figure B-3. Vehicles Tested in the Lockheed-Georgia Low-Speed Wind Tunnel (Continuation 7)

51 • q.

0.411 0.783

t' •

• o.c;nJ I • b Jll

Figllt't' 8-1. Vt·hi~l.·:t Tc.":ttc",1 in th,' t.",·kh.·.·d-t:.·.,t'lti,I t,'V-SI'c"t'" Wind Tllnn.·l (C.,nt inll'It i.,1t ~n

( '1..- ••• '<0 •• ,:,\,:\ 1 t" \ • • ft. ..., ~. p. \'.C' !'~")1\ " · ,- (il'.\: - ..

• •

I.

"~ndn Civi~ Wagon

Co o 0.514 1.685 0.866

t.

.F:- • -

Ford Fit'st.1 ., ., At m- ~o At Ill- CD 0 0 0.468 1.747 0.818

Figure B-3. Vehi~les Tested in the Lockht'ed-Georgia Low-Speed Wind Tunnel (Continuation q)

51

• APPENDIX C A UV1!W or· CDlIAL AnC)DtlWflC DRAG • PUDICTIOlf PIlOC!DUlES, APPLICATIOlf, AID UTILITY

A. DRAG !STtKATIOlf M!TRODS ( • Several aerodyn.. ici.t. have attempted to make ..neralilation. or to predict a vehicle'. drag ba.ed on various Ihap' characteri.tic. (Reference. 3-1, 3-2, and C-l). The u.ual method i. to a ••emhle a large data base and develop correlations. 'erhapi tbe be.t known effort i. that of R.G.S. White (Reference 3-1) of Britain's Motor Indu.try Research A•• ociation (KIRA). Wind tunnel te.t. of 141 different vehicles were utilized. Bach vehicle va. divided into .iz ba.ic zones, three of whieh were further .ubdivided. Humbers were assigned to features in each zone or subzone in an attempt to rate their obstructive effects on the airflow around the vehicle. Rating values were assigned to each of the nine categories depending upon the vehicle's shape in those zones. The predicted drag coefficient was then deterMined from the following empirical equation:

CD • 0.16 + 0.0095 x Drag Rating

where the Drag Rating is sim~ly the summation of the nine individual category ratings.

By way of verification, drag estimates for 20 vehicles (mainly European) were made by White using this procedure, and wer~ then compared to measured values. The average scatter was about 7%. It should be pointed out that the drag of these vehicles was not particularly low, and that WIthe's procedure would not necessarily reflect the subtleties inherent in drag-optimized vehicles. Another cautionary note is that meaeured MIRA drag values are substantially lower than similar measurements made in domestic wind tunnels. The real value of this effort is the relative ordering of the aerodynamic design consequences of several shape parameters. A second, and less rigorous "drag rating" approach to drag estimates is presented in Reference C-l (Cornish). Ten regions are defined and a rating of from 1 to 3 is assigned. On this basis, the most streamlined vehicle would have a rating (R) of 30 and the worst, a rating of 10. The resulting drag coefficient is then calcalated from

CD • 0.62 - O.OlR This procedure is rather crude but simple and its accuracy is far less than the 7: reported for ~ite's method.

55 PR[CEDfN(i "A\JL BLANK at i~CT F'!.~.!J

• Both of the two previous procedures are baaed upon shape correlation curves Which are linear with the drag ratins and are liaited to conventional passenger vehicle configurations. A third­ eltiaat\on procedure, developed for the EPA (Pershins - Reference 3-2), is a "drag buildup" _thad baled on quantitative geOMtric characteristics applicable to a large range of generic body shapea. The total vehicle drag coefficient is defined as the lua of the coefficients of 11 dilcrete parts. 11 - I: CD. i-I 1 Although this procedure requires more quantitative knowledge of the body shape being evaluated, it has the potential of addressing the more subtle details.

Excerpts fro. theae three references follow; sufficient detail is included to allow their application. In addition, soa. Reneralizations are set forth concerning the drag increments characteristic of various components and devices.

B. ORAG ESTIMATtON PROCEDURES

1. Drag Coefficient Estimation (R.C.S. White - Reference 3-1)

White divides a vehicle into six zones and three subzones for 4 total of nine categories. These are listed in Table C-1. A rating number is then assigned to the particular vehicle characteristic in el\ch of the nine c3tt'gories (see Table C-2). Thl.!se nine intermediate ratings are sU1lllDed to yield the "drag rating." The resulting drag coefficient is calcul3ted from

CD • 0.16 + (O.OOQS) (Dr3g Rating)

Table C-l. Basic Vehicle Zones (Rl.!ference 3-1)

Zone Subzone Category

Front (3) Outline pl3n 1 (b) Elevati~'n 2

~Jindsh i~ ld/Roof Junct ion (3) Cowl 3nd fender cross section 3 (b) WindshielJ pl3n Roof (3) WindshielJ peak 5 (b) Rl'of ~lan (, Rt'ar Roof/Trunk 7 Lowf'r Re.1 r-F.nJ 8 Table C-2. Dra. latina S1steal

CatelOry• 1. 'ront Ind Plan Outline latins Approxi.atel, s ..icircular ([ 1 Well-rounded outer quarters [[ 2 Rounded corners without protuberances [[ J Rounded corners with protuherances Ca) [[ 4 Squared tapering-in corners [[ s Squared constant-vidth front [[ 6

Category 2. Elevation(b) Rating

Low rounded front, sloping up 1

High tapered rounded hood

Low squared front, sloping up 2

High tapered squared hood

Medium height rounded front, sloping up 3

Medium h~ight squared front, sloping up 4

High rounded front, with horizontal hood

High squared front, with horizontal hood 5 . lAdapted fro. Reference 3-1 •

57 "

Table C-2. Drag Rating S,ltea (Continuation 1)

Catesory 3. Cowl and render Croll-Section -Windlhield/Roof Junction

rlush hood and fenders, well­ 1 rounded body sides

High cowl, low fenders 2

Hood flush with rounded-top fenders 3

High cowl, with rounded-top fenders

Hood flush with squared-edged fenders 4

Depressed hood, with high squared-edged fenders 5

Category 4. Windshield Plant(c) Rating Full-wrap-around (approximately semicircular) [I 1 Wrapped-around ends DC 2 Bowed IT 3 Flat IT 4 Category 5. Windshield Peak Rating

Rounded 1

Squared (including flanges or gutters) 2

Forw3rd-projecting peak 3 .

58 Table C-2. Dra. latinl SYlt.. (Continuation 2) • Catesory 6. Roof 'lan latinl

Ve11- or ..di~tapered to rear 1

Taperinl to front and rear (.. x. "idth at Be POlt> or D 2 approx~telycon.tant "idth u

Tapering to front (.. x. width 3 at rear) o

Category 7. Rear Roof/Trunk(d) Rating

Fastback (roof line continuous to 1 tail)

Semi-fastback (with discontinuity 2 in line to tail)

Squared roof with trunk rear 3 edge squared ~ Rounded roof with rounded trunk ~ 4 Squared coof with short or no trunk ~ • Rounded roof with short or no trunk ~ 5

59 - ~.. ~----.- -..

Table C-2. Dra. aatina 51It•• (Continuation 3)

Cateaory 8. Lower aear End latiaa Well- or aediu.-tapered to rear :JD 1 s.&ll taper to rear or conltant width :JJ 2 Outward taper (or flared-out final =rJ 3 Cateaory 9. Underbody(e) Rating

Integral, flush floor, little projecting mechanism 1

Intermediate 2

Integral, projecting structure 3

Intermediate 4

Deep chassis 5

(a) ~ender mirrors. Include in protuberances if at the fender leading end. Otherwise add 1.

(b) Add: ) for separate fenders; 4 for open front to fenders (above bumper level); 2 for raised built-in headlamps; 4 for small separate head lamps; 7 for large separate headlaaps.

(c) Add: 1 for upright windshield; 1 for prominent flanges or rain gutters.

(d) Add: ) for high fins or sharp longitudinal edges to trunk; 2 • for separate fenders. Note: In all the ratings in this column, the trunk is assumed to be rounded laterally. (e) Intermediate rating~ applied from vehicle examination. NOTE: Throughout table, the word "taper" or "tapered" refers to the plan view.

60 ------.-~ --. --.-.,.--- -p-- -- ,- -.-~-.. -

2. D~al Coefficient !.t~tion CJ. J. Co~ni.h - Refe~ence C-l)

Co~ni.h divide~ a vehicle into 10 sone. and a •• ign. a .ub~atinl of f~o. 1.to 3 to each of thea C.ee Table C-3). The total ~atinl' a, i. the .u. of the.e 10 .ub-~atinl'. Tvo vind.hi.ld sone it... Cnuabe~. 4 and 5) refe~ to the elevation and plan viev., ~e.pectively. The re.ultinl d~al coefficient i. calculated from

CD • 0.62 - O.OlR

Table C-3. Aerodynamic Ratinl

No. teem 1 2 3

1 C:rill Blunt; square Fai~ly sloped Well sloped

:! Light!! Open; exposed Partially inset Well faired

3 Hood Flat Fairly sloped Convex, sloped

4 Windshield Steep Fairly sloped Well sloped

5 Windshield Flat Fairly cu~ved Well curved

6 Roof top Open Fairly sloped Convex, sloped

7 Rear Window Notched Fairly sloped Fastback type

~ Tr.ank Cut off square Fairly sloped Fastback type

9 Wheels Exposed Partially closed Well concealed 10 Underside Exposed Partial pan Full pan

61 3. Drag Coefficient Estimation (B. Pershing - Reference 3-2)

• This procedure i. much more complicated but much less subjective than .the previous two. The relevant vehicle dimensions and areas are illustrated inPigures C-l and C-2. The total drag coefficient is defined as the s~tion of eleven component coefficients:

•

The details of the determination of the ith components follow (reproduced directly from Reference 3-2). An assessment of this procedure is given in Reference 3-3.

front End Drag Coefficient, CDI

where

AR a total vehicle projected frontal ar~a, ~2 (ft2) AF • front end projected area, m2 (ft2) R a edge radius, m (ft) F. a running l~ngth of the edge radius, m (ft)

an~ the sub~cripts u, 1, and v refer to the upper, lower. and vertical edges of the front ~nd, respectively. The (R/E)i lr~ to be tak~n as 0.105 when the estim~ted values exceed this magnitude.

Windshield Ora~ Coefficient, CD2 ., C.,s - Y

• wh~re

Aw s "rojected area of windshield, ~2 (ft2) ~ s 110pe of the windshield measured from the vertical, Je~ t3 2 2')'

62

• ------~~.-=------==:=..:======:::--=---::=. =-=-.--~.--====------

• w ) ) ......

~------L------~

Figure C-l. Vehi~le Dimensions (Reference 3-2)

FASTIACK NOTCHIACK HATCHIACK

2.0

-...z Q 0.8 ...... o u 0.4 C) ~ Q O~~~~----~--~--~----~--~----~--~----~--~ o HATeHIACK SLOP£,. - dee

Figure C-2. Hatchback-Notchback Drag Coefficient Ratio

63 and the subscripts u' and v' refer to the roof-vindshield inter.ection and the windshield posts, re.pectively. The value of co.'" 18 to be taken as zero for'" larger than 45 degree. and the (R/E)i are to be taken a. 0.105 for e.tiaated value. exceeding this ..gnitude.

Pront Rood Dra, Coefficient, CD3

where An • projected area of body below the hood-windshield intersection, .2 (ft2) Lh • length of hood in the elevation or side view, 111 (ft) 'and the quantity (Ah - Ap) is to be taken as zero if it. 'is negative.

Rear Vertical ~dge Drag Coefficient, CD4

Co • -0.19 for (:v) < 0.105 4 (~v) (~)

• -0.02 (;b) for (:~ > 0.105 where

Rv • radius of rear vertica~. edges. 111 (ft) W • ve~icle width, 111 (ft) Eb • length of rear vertical edge radius, 111 (ft) H • vehicle haight, 111 (ft) .

Sase Region Drag Coefficient, CDS

•

where

A~ • projected area of flat portion of base region AM • projected area of upper rear or hatch portion of base region measured from the upper rear roof break (or for smoothly. curved rooflines, that point where the roofline slope is IS degrees) to the top of the flat base, m2 (ft2) COS • drag coefficient of the flat base

• 1------~------~q------~~H

COft • drag coefficient of the upper re~r or hatch portioQ of the ba.e region

and the ratio (CD/CDR) is shown in Figure C-2 •• a function of q" the angle of the linl fra. the u?per rear roof break to the top of the flat ba.e a. measured fra. the hori~ontal.

Underbody Drag Coefficient, C0 6

", C • 0.025 (0.5 - x/L) (~) for 0 ~ x/L ~ 0.5 D6 \"R • 0 for x/L > 0.5

where

~ • smoothed forward length of the underbody, m (ft) L • vehicle length, m (ft) A? a projected plan area of the vehic!e, m2 (ft2)

'Jheel and Wheel Well Drag Coefficient, C0 7 Co -0.14 7 Rear Wheel Well Fairing Drag Coefficient, CDS

CD8~ -0.01

?rotuberance Drag ('oefficient, COg

1 • 1 A p. J

Apj a projected area of jth protuberance, m2 (ft~)

~u~let ~irror Drag Co~fficient, COlO

where

.~ ~ projected area of mirror with bullet fairing, m2 (ft2)

6S

• Cooling Drag Coefficient, CDII

, vhere

• radiator area, m2 (ft2) • exit velocity of cooling air from radiator • 0.233 [1.0 - k (u/lOO)2]

and

k • 1.14C (m/sec)-2 [or 0.299 (mPh)-2]

4. nrag Increment Generalizations General rule-of-thumb values have been given to many interference components and drag reduction devices. These are helpful only in the broadest sense; that is, most effects 'are a function of the specific application. For instance, a front air dam (or chin spoiler) might significantly reduce the drag fer one vehicle but inerease it for another. Similarly, some lov-drag device may be detrimental at a yaw angle. Such dramatic results, however, are generally reserved for special cases. If one limits the application to an "average, conventional sedan," perhaps the generalizations in Table C-4 can provide some guidelines. The increments should not be considered as purely additive; this is particularly obvious in the case of an underpan and air dam.

66 Table C-4. Drag Increment Generalizations

Component or Configuration CDo (%) • Reference (s)

Full length underpan -5 to -15 3-8, 3-10, C-2, C-3

Pront "chin" spoiler (air dam) -6 to -9 3-8, 3-9, C-4

Rear deck spoiled (lip) -5 to -9 3-8, 3-9, C-3, C-4 Flush windshield and side glass (no raingutters) -3 to -7 3-10, C-S

Wheel discs and rear fender skirts 0 to -2 3-10, C-4 Sideview mirror(s)

Conventional A - pillar, stalk mount +1 to +4 3-10, 8-4, C-5

A - pillar, integral mount +1 to +2 3-10

Fender mount (two) +6 3-10 Head lights

Pop-up +3 to +6 3-10, C-6

Pocket +3 to +6 3-10

Open front windows 0 to +3 3-8, C-2, C-6

Body side rubstrip +1 3-10

Road trim package 1 +2 to +8 3-10, 8-4,

•

1 Consists of conventional mirror, windshield wipers, door handles, license plate, bod~ ~aps.

67

• APPENDIX D APPLICATION or AREA-DISTRIBUTION SMOOTHING PROCEDURES TO AUTOMOTIVE AERODYNAMIC DESIGN • Basic Principles Since early times, man has recognized that certain shape. found in nature move more efficiently through air and water. The hulls of even primitive ships were often modeled after the well-known tear drop-shaped body exhibited by many fish and birds. It was therefore only logical that early attempts to streamline automotive shapes were approached in a similar manner. These often toot the form of a "torpedo on wheels" or the superposition of several "half drop" shapes. However, these potentially low drag designs were often severely ~ompromised by many unfaired appendages such as wheels, lights, suspension members, open cockpit. and the like. The basic principle demonstrated by low drag bodies found in nature, however, can still find application in road vehicles. A "streamlined" body has low drag by virtue of well attached flow (no boundary layer separation) and the resultant minimum size wake. This boundary layer (flow immediately adjacent to the body surface), will remain attached as the flow negotiates its way along a smooth body so long as its momentum is sufficient to overcome any adverse pressure ~radient. Momentum loss, however, is a function of the body surface contour grarlients in the direction of flow. A well streamlined body has only moderate contour gradients whereas a modern automobile is characterized by many steep gradients. A representative contour parameter suggested by Hucho in Reference 3-4 is the line integral of the rate of change of curvature along the body surface. ror simplicity, Hucho considers only the integral along the body centerline but it is recognized, that it should be applied over the entire body surface. Although theoretically possible, this would require a tremendous effort. The present principle suggests a simple, if imperfect, compromise. The distribution of cross-sectional area as a function ~f longitudinal station along the body may be an approximation, representative of an integrated body contour parameter. The area distribution principle may be stated thusly:

"Gradual area variations along a body length are characteristic of a streamlined design." It is pointed out that this may be a necessary, if not sufficient, attribute. Clearly, one could conceive of a shape satisfyin~ the smooth area distribution criteria with cavities opposiee sharp lumps and bumps canceling their effect. In order to minimize that particular anomaly, a corollary is added to the principle: "The body camber-line should be as smooth as possible."

f'RECfD1N(; ?~. ::. ..r .... ,~ ",_1- ro.' .... ~- 69 . I"'t_~ ...... tI·.• ". ."- • ,.~.:..J -- Here the camber-line is defined as the locus of points connecting the centroids. of the cross-sectional area slices. Although the emphasis is differentl these siaplified principlel are in general agreeaent with Reference 3-5. • Procedure

The application of the area distribution and camber-line principles represents an atteapt to provide an intermediate alternative to costly developmental wind tunnel testing. Although the procedure relies heavily on perceptive decilions, it doe. produce an analytical/graphical evaluation process which iteratively guide. one to a more streamlined design.

Before the process can be implemented it is necessary to have rather detailed_ three-view 10ft drawings or station teaplates of the candidate body. Section views may then be created at about 5 to 10 cm intprvals (full-scale) along the longitudinal axis (more frequently where the area is perceived to be changing rapidly and fewer where the area change is less dramatic). A planimeter (or other-means) may then be used to measure the area of each cross section. The areas, thus determined, are then plotted as a function of station position. Figure 0-1 is a schematic example of the procedure and the result. The diagram created in this manner is called the body "area distribution. It Those regions where the area is changing rapidl~ are candidates for modification. However, in order to help guide these modifications, the corresponding body camber-line should be developerl. As indicated earlier, this is merely a plot of the section area centroids versus station position. An easy way of determining the centroid of a section area is to first cut the shape out of a piece of stiff paper or cardboard. Next, suspend it from a pin near the perimeter at some arbitrary point (such that it's free to rotate) and draw a vertical line through the pin hole. Rotate the shape about 900 and reppat. If the material is homogeneous, the intersection of the two lines will be the centroid. Obviously, the point should lie midway between the sides of each section or the design is not l~terally symmetrical. The vertical displacement from some reference such as the ground varies from section to section. These measurements when plotted versus section position, produce the body camber-line. (This result is also depicterl-in Figure D-l.) With the added constraint that the camber-line be as smooth as possible, the sections reql1irin~ area modifications are reexamined. If it appears that some area needs to be added at a few stations (in order to smooth the hood/windshield interface, for example) and the camber-li~e is low in that rel'tion, then the area should be added near the upper surfaces. tf the camber-line could be smoothed by lowering it in that region,

l'forelli, in developing his "Body Shape of Minimum Drag" (Reference 3-S), be~ins by defining a specialized camber-line and bases the body shape upon it.

70

• x

AREA DISTRIBUTION

CAMBER LINE ~ /

•

Figure 0-1. Schematic Showing Area Distribution Procedure

71

• the area should be added below the centroid. It is generally advisable to make this area addition around the rocker panel rather than under the body. The technique is iterative, and the area distribution and camber-line curves should be checked following each complete modification. Quite clearly, this procedure cannot be mindlessly applied, but rather requires a blend of artistic ~tyle and sensible judgement. Certain individuals may be able to accomplish much the same result by "integrating with their eye" but in any event, this technique provides a methodology to measure the designer's . intuition.

Examples The General Electric ETV-I represents an exceptionally well integrated low-drag (CD • 0.3) vehicle body (Figure D-2a). It waa o designed by Chrysler using subscale developmental wind tunnel test techniques on a series of clay models ,(Reference B-5). Nevertheless, it is interesting to examine ita area distribution in order to teat the area distribution principle. That is, does this low-drag vehicle exhibit the gradual area variation typical of naturally streamlined bodies? Figure D-2b shows that the ETV-l area distribution is fairly s~ooth. However, without some basis for comparison it is difficult to assess whether a particular area curve is exceptional or whether there is room for improvement. An example of a low drag design, near the extreme practic~l limit for an automotive shape, was developed using the area distribution technique described earlier and verified in subsequent wind tunnel tests (Figure D-3a).1 The styling theme is clearly reminiscent of the "Body Shape of Minimum Drag" developed by Morelli (Reference 3-5). The area distribution resulting from this very streamlined, low-drag design is shown in Figure D-3b. Obviously, the gradient is smooth since the desi~n was refined using that technique. Hllth the ETV-l an':! this design (Mays-B) are drag-optimized shapes for their respective de~ign themes. tt should be pointed out, however, that the former was developed through costly wind tunnel develop~ental testing (equivalent to a Level ttt Design) and the latter using the area gradient principle (equivalent to a Level II Design).

A third example is the Garrett· AiResearch ETV-2 electric vehicle (Figure D-4a) which employed neither of these processes during desi~n. In fact, this vehicle is representative of a Level I Design. As shown in Figure D-4b, the are4 distribution of the Garrett vehicle

IThis work was performed under subcontract to the Art Center College of Design in Pasadena 3S a student project by J.e. Mays (Reference 0-1). This outstanding design was found to have a CD - 0.2 from o clay mode! ".lind lunnel tests. Further alterations in the tunnel paid n? drag dividends; it had indeed been drag optimized on paper. (~ince the model lacked a certain level of detail, which would be present on an actual vehicle, it is estimated that a prototype version might have a drag coefficient around 0.25.)

72

• Figure D-2a. General Electric ETV-l

Figure D-2b. Irea Distribution and Camber-Line for tt.~ General Electric ETV-l

73

• Figure D-3a. Mays Aero Car (Model)

AtEA DISTCIBUTtCN

CAMIUllNE

Figure D-3b. Area Distribution and Camber-Line for the Mays Aero Car

74

• ---... ~ '.0- .~ - .... ,,:,... • ... ~ .. ' .• ;._ ,~.. r+;. '.~ .

Figure D-4a. Garrett AiResearch ETV-2 II

Figure D-4b. Area Distribution and Camber-Line for the Garrett AiResearch ETV-2

75 ~.~. -~- ' . ___ ~",-=....c..-,-.-"--,----_. ---. ___~",;,;",--,;;,_ _... ----.

is signific4ntly roulher than either of the other two vehicle shapes. This i. consistent with full-scale wind tunnel te.t re.ult. which found the Garrett draa coefficient to be about 0.4 <.ianificantly Ireater than either of the other two exa.ple vehicle.) • • The •• fev enapl•• by no .an. provide conclusive proof of the area distribution principl. but there i. sufficient evidence of its valu. to include it a. 4 part of the d•• ian .trate.,.

16 APPENDIX E

ESTIMATING DRAG CHARACTERISTICS IN YAW POR AUTOMOBILE SHAPES •

Since • ro.d vehicle oper.tes in the presence of ..bient vind. which .re r.rely .ligned vith it. longitudin.l .xi., .088 ~ovledl. of the rel.tion.hip betweea dr.g .ad y.v .agle i. aec•••• ry. Th. fir.t .nd mo.t .ignific.nt effort to quantify .nd lener.li.. th•• e characteristic. for auto.otive .h.pe. v •• perfor.ed by Bartb of the Stuttgart Technical College (Reference E-l) two d.cade. ago. Limited to .ide force and yaving moment coefficients, hi. r •• ult. vere derived from vind tunnel tests of four basic .hape. and four group. of small automobile models totaling 2S specimen. in .11. H. -.hoved that variations vith yav angle vere generally linear (up to 250 ) and that differences in body form and feature. affected only the .lope of the variation. The body features upon vhich B.rth based hi. correlation. were aspect ratio and fineness ratio. Ten years later, recognizing the need to generalize yaw effects for all the aerodynamic coefficients (particularly drag), Bowman of Ford Motor Company compiled vind tunnel data on 3/S-.cale models of 21 automobile body forms (Reference 3-6). Suggesting that the range of aspect ratios for prevailing American sedans vas not sufficiently large enough to provide a suitable correlation parameter, he looked for non-geometric relationships. Specifically, he determined that the drag-yaw characteristic had a typical maximum of about 300 and the amplitude was a function of the drag coefficient at zero yaw. Bowman's general equation vas of the form:

(E~l)

where Kl is a function of CD (the zero-yaw drag coefficient) o and a few general shape description~; ~ is the yav angle in degrees. tn an effort to correlate the model and full-scale wind tunnel data developed during the present program, it was determined that BOW'lll4n's representation was entirely inadequate to represent the range of vehicles investigated. Since extensive model tests had been performed on the effects of aspect and fineness ratios for automotive shapes (see Appendix A), these data were examined for yaw characteristic correlations. Using a formulation format similar to Bowman's, the following equation was derived:

CD/CD- 1 + K(1 - cos 61/1) (E-2) o

where K is not a function of CD but a function of aspect ratio o (AR) and fineness ratio (FR). That is, .. K - (0.l5AR - 0.03)FR - 0.513AR + 0.336 (E-3)

71 ...... -._- ._- .... -._-.------

where AR is the ratio of body height (not including ground clearance) to body width, and FR is the ratio of body length to the diameter of a circle equivalent to the body frontal area.

~he fit to the experimental data is quite good, as is shown in the following table: ...

AR FR K K measured Eq. E-3

0.58 2.2 0.16 0.16 2.7 0.19 0.19 3.2 0.22 0.22

0.70 2.2 0.13 0.14 2'.7 0.18 0.18 3.2 0.22 0.22

0.77 2.2 0.14 0.13 2.7 0.19 0.17 3.2 0.22 0.21

a.88 2.2 0.10 0.11 2.7 0.14 0.16 3.2 0.16 0.21

r.ncouraged by this clear correlation, Equation E-3 was applied and comp~red to the results of the full scale prototype wind tunnel tests (Reference 2-1). Because the simple AR and FR parameters did not adequately describe the details of each vehicle shape, the correlation was not nearly as good. However, for design purposes, this equation should suffice for typical hatchback or fastback subcompact vehicles. A few. modifying comments are necessary, however, for vehicles with sp~cifically distinctive characteristics.

78 tn sUlII11ary, the variation of· drag with yaw angle can, to a first approximation, be described by the following function and associated cOlllllents:

(E-2) ... where

K • (0.l5AR - 0.03)FR - O.5l3AR + 0.336 (E-3)

o Not valid for fineness ratios less than 1.5.

o Reduce K by up to 50% for extremely low nose and sloping hoodlines.

o Increase K by up to 10% for harsh, angular design with corner radii less than 10 em.

o Increase K by up to 15% for notch back designs.

Note that a maximum is reached at r1J '" 300 such that.

Co IC '" 1 + 2K (E-4 ) max o()

This parameter is useful in predicting the effects of a~bient winds in Appendix F •

...

79

• ___ 4 ___ ••"'" • ___-.... ~ .. _~ ____• ______

" - - .

APPErmIX F DETERMINATION OF DRAG wtND-WEIGHTING FACTORS FOR VEHICLES OPERATING IN AMBIENT WINDS r

As a vehicle moves along a roadway, it normally operates in a windy environment. Since the wind vector is usually not aligned with the highway, the vehicle is effectively yawed with respect to the flow. Therefore, range prediccions tb~t utilize the zero-yaw drag valu~s will inaccurately characterize the aerodynamic contributil)n and yield optimistic results.

A procedure to accurately determine the effects of ambient winds on vehicle drag has recently been developed (Reference 3-7). Th~ approach is to figuratively ~in a computer'simulation) dri~e a vehicle over a prescribed velocity-time schedule in the presence of ~ wind which varies statistically in speed (a speed probdbility function designated by some annual mean win~ speed) and ~omes with eQual proi:ability from any direction. The resultanc combination of the vehicie and wind velocity vectors yields an instantaneous yaw angle with r·"!spect to the vehicle. If the vehicle's drag-Y2w characteristic is knolln or .:issumed, the resultant drag !II.ly be determined at each instant. Therefore, tne energy required to overcome aerodynamic resistance is calculated by integrating the instantaneous aerodynamic power required over the entire cycle. It is then possible to determine the ccnstant drag coefficient that would have been necessary in order to yield the same result. Tbe ratio of this new effective coefficient, CD ,to the or:ginal zero-yaw drag coefficient, eff CD ' is the wind weighting factor, F. F is thus a mul~iplieT to o correct the zero-yaw drag coe fficient for the effec'ts of ambient winds.

This rigorous procedure was used to generate F-factors tor 1 large range of vehicle characteristics, wind conditions, and driving cycles. Analysis of these results 1ielded many fortuitous relationships leading to simplifying assumptions which are accurate to within about 3%.

The wind-weighting factor, F, was found to be a simple exponential function of the dominant parameter, Co IC ; ~he D max 0 yaw angle where CD occurs (", .. 30 0 :. 50) is of second order max significance and is neglected. For design purposes, the parameter estimated by a ~haracteristic CD ICD may be special case of the yaw max 0 equation presenced in ~ppendix E (F.quation E-4). F is then only a (unction of jaw angle, the annual mean wind speed and the partica1ar driving cycle or constant speed. The resulting equations for Fare siven in Tables F-I and F-2 in metric and English units, respectively.

.'., It ":. 81

• Table F-l. Wind-Weighting Factor Equations - He:ric Units

W • annual mean wind speed in km/hr (12 ~/hr .ean average in U.S.) V • vehicle speed in km/hr EPA CYCLES ,. URBAN: F • (1.22 x 10-4w2 + 1.61 x 10-2W)x(Cn_ leo) + 2.89 x lo-4w2 -max 0 -·1.47 x IO-2w + 1.0 HIGHWAY:

F - (1.94 x lo-4w2 + 5.61 x lo-lw)x(Cn leo) + 2.86 x IO-5w2 -max 0 - 5.32 x lO-lw + 1.0

COHBINED: (55% - 45% split):

F - 0.72 x 10-4w2 + 1.11 x 10-2W)x(Cn ICD) + 1.40 x lo-4w2 -max 0 - 1.11 x 10-2W + 1.0

SA! ELECTRIC CYCLES (J227a)

B: F - (9.41 x 10-5w2 + 3.76 x 10-2W)x(Cn IC ) + 5.97 x 10-4w2 -max D0 - 2.83 x _10-2W + 1.0

C: F - (1.18 x 10-4w2 + 2.22 x 10-2W)x(Co. I CDo) + 3.61 x 10-4W2 llax - 1.94 x 10-2W + 1.0

D: ~ - (1.81 x 10-4w2 + 1.25 x 10-2W)x(CDmax/CDo) + 1.44 x 10-4w2

- 1.33 x 10-2W + 1.0 CONSTANT SPEED

F - ~.98 (WV)2 + 0.63 (W/V~ x(CDmax/CDo) - 0.40 (W/V) + 1.0 Constraints: 1

For (W/v) < 0.09 F - 1.0 For (w/v) > 1.0 (w/V) - 1.0 .~

lThese constraints may be necessary if this equation is applied to the quasi-steady instantaneous vehicle speeds in a computer simulation (i.e., the function goes to infinity at V • 0). In a physical sense, however, the equation is entirely proper without these boundary conditions.

82

'. Table F-2. Wind-Weighting Factor Equation - English Units

W • annual mean wind speed in mph (7.5 mph mean average in U.S.) V • vehicle speed in mph

EPA C"{CLES

URBAN:

F • (3.16 x 10-4w2 + 2.59 x 10-2W)X(Cn IC ) + 7.49 x.lo-4w2 -max O0 - 2.37 x 10-2W + 1.0

HICHWAY:

F • (5.02 x 10-4w2 + 9.04 x 10-lw)x(Cn IC ) + 7.41 x 10-Sw2 -max o0 - d.56 x 10-lw + 1.0 COMBINED: (55% - 45% split):

B: F = (4.47 x 10-4w2 + 1.78 x 10-2W)x(Cn IC ) + 3.62 x 10-~~2 -max O0 - 1.79 x 10-2W + 1.0 5AE F.LF.CTRIC CYCLES (J227a)

B: F ~ (2.44 x 10-4w2 + 6.06 x 10-2W)x(Cn ICO) + 1.55 x 10-3W2 -max 0 - 4.56 x 10-2W + 1.0

C: F = ().07 x 10-4w2 + 3.57 x 10-2W)x(Cn ICO) + 9.37 x 10-4W2 -max 0 - 3.12 x 10-2W + 1.0

0: F = (4.68 x 10-4w2 + 2.01 x 10-2W)x(Cn ICO) + 3.73 x 10-4W2 --max o· - 2.14 x 10-2W .. 1.0 CONSTANT SPEED

F = [0.98(W/V)2 + 0.6)(W/V)] x(CDmax/Coo) - 0.40(W/V) + 1.0

Constraints:

For (N/V) < 0.09 F = 1.0 For (W/V) > 1.0 (W/V) = 1.0 ,-

,..

83 In order to further simplify the application, Figures F-1 and F-2 are is presented. These are graphical representations from Table F-l with the annual mean wind speed fixed at 12 km/hr (7.5 mph);1 this is the average condition across the country.

Therefore, in the course of the design process, after the • zero-~aw drag coefficient, CD , has been estimated, the effective wind weighted coefficient CDe~f may be determined by

/I (1) Calculating the Cn _ IC ratio from Equation E-4. "'111 a x D0 (2) Det"rmining F, for the design cycle, from Figure F-1 or F-2.

(3) Calculating, CDeff • F x CDo. An example to demonstrate just how important the wind weighting analysis might be in making drag estimations is presented in Table F-3. Using the vehicles in the EHV Aerodynamic Data Base (Appendix B, Part C), the effective wind weighted drag coefficient, CD ,was eff determined (for operation over a J227a D cycle). In this case the Cn ICn ratio was precisely known for each vehicle from wind max 0 tunnel test data at yaw angles up to 400 • Therefore, the wind wei~hting factor, F, could be directly determined for each vehicle from Figure F-l (for an annual mean ~ind speed of 12 km/hr). The effective drag coefficient, COeff,is, as before, the product of F and Co o • As can be seen, the wind-weighting factor, F, averaged about 1.08 (an R% correction), ranging from 5 1/2% to almost 12%. Had this :tnalysis been pp.rformed for a "B" cycle, the correction would be as high as 42%. (The wind vector is more of a factor at lower vehicle speeds; however, the aerodynamic component is smaller portion of the total energy requirements.)

Itt should be noted that this is not a constant average speed, but rather a statistical average. For instance, an annual mean wind spped of 12 km/hr has winds of up to 50 km/hr occurring about 3% of the time and winds less than 12 km/hr occurring about 70% of the time.

84 I.~ • ~ ..' eu :! 1.3 ~ . Z ;:: 1: ~ W .,; 1.2 0 Z ~

1.1

::

Figure F-l. l.'lnd-Weighting Factors for Various Driv1.nl; Cl-'c1es

NATIONAL AVERAGE ANNUAL MEAN 1.3 WIIljD SPEED· 12kph (7.5 mphl ...~' ~\.'t., e'" IP "f,Y". ~... 1.2

1.0

1.0 1.2 I.~ 1.0 t"_ 'e "MAX 00

Figure F-2. Ambient Wind Drag Factor as 3 Function of Various Constant Speeds

85 Table F-3. Effective Wind-Weighted Drag of Test ~p.h.cles Performing J227a D Cycles in the Presence of a 1; kph Annual Mean Wind Speed Equally Probable From Any Direction (Windows Closed)l

.'" V~hicle C m2 Co CD . ICO F CD !., 0 max 0 °eff . eff .. GEr.TV-l 0.308 1.27 1.084 0.333 0.614- .- Garrett ETV-2 0.395 1.50 1.124 0.444 0.9900 GE Centennial 0.337 1.12 1.058 0.357 0.660 CDA Town Car 0.367 1.16 1.065 0.391 0.686 SCT Itabbit 0.459 1.26 1.082 - 0.496 0.903 Sebring-Vanp,uard 0.541 1.20 1.072 0.580 0.986 Citicar Za~ato F.1car 0.490 1.37 1.102 0.540 0.992 Jet 600 Van 0.530 1.40 1.107 0.586 1.138 otis Van 0.581 1.30 1.090 0.633 1.641 Kaylor GT 0.583 (2) F.ner~y R&D HEVAH 0.497 (2) MolC Pacer llagon 0.406 1.27 1.085 0.441 0.980 A.'1C P3cer <;edan 0.450 1.24 1.079 0.486 1.07') Chevrol~t Corvette 0.490 1.10 1.055 0.517 0.995 Ol·isl'\obi II! Delta 138 0.558 1.46 1.118 0.624 1.296 S('ri:1n ~hpvrolet Chevette 0.502 1.14 1.062 0.533 0.941 Plymouth Horizon 0.411 1.32 1.093 0.449 0.880 Honrla Civic ~e1an 0.503 1.28 1.086 0.546 0.890 qonda civic Wagon 0.514 1.22 1.076 0.553 ().932 Ford Fiesta 0.468 1.22 1.076 0.504 0.880

ItHth front '..lindows open, the CD ICo ratio increases by max 0 an avp.l"age of 16% for this group of vehicle. 2Maxt'!\um Cn was not determined since test yaw angle was limited to 20 degrp.es.

• .-,

86

End of Document