E AME ICA SOCIE Y O MEC A ICA E GI EE S 88 G 228 4 E. 4 S ., ew Yo k, .Y. 00
e Socie y s a o e es o si e o s a eme s o o i io s a a ce i a e s o i is cuss o a mee i gs o e Socie y o o i s i isio s o Sec io s o i e i i s u ica io s. iscussio is i e o y i e a e is u is e i a ASME ou a . a e s a e a ai a e: ] om ASME o i ee mo s a e e mee i g_ i e i USA Copyright © 1988 by ASME Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021
Com a iso o Ce amic s. A a ce Su e a oy O io s o a Sma Gas u i e ec o ogy emo s a o
. O EMIS A, . A IE Su s a u omac Sa iego
A S AC requirements can be cost-effectively fulfilled by the simple cy- cle gas turbine operating at relatively low pressure ratio and The next generation of small gas turbines used as com- turbine inlet temperature without the benefits of multi-staging pact Auxiliary Power Units (APUs) in aircraft and mobile and turbine cooling as customary on larger propulsion engines. ground power applications will achieve higher power density The need to increase the power density without sacrific- than current installations by operating at substantially higher ing simplicity and cost demands higher pressure ratios and cy- turbine inlet temperatures. Ceramics vs. advanced/cooled su- cle temperatures resulting in a corresponding increase in stage peralloy designs are compared as alternate paths to improved loading and wheel tip speed. Figure 1 shows the estimated p rf r n thr h n r d t rb n nl t t p r t r f r specific power output of a small APU as function of turbine the T-100 MPSPU (Multi-purpose Small Power Unit) technol- inlet temperature (TIT) and pressure ratio based on the ex- ogy demonstrator engine currently under development. pected component efficiencies. The increased aero-thermo re- Past experience at Sundstrand Turbomach in demonstrat- quirements require advanced structural materials, better (inno- ing ceramic and air cooled components is used to project level vative) utilization of the material properties and a reassess- of success expected in meeting the demonstrator engine per- ment of accepted cooling techniques. formance goals with either ceramics or advanced/cooled super- An advanced small gas turbine APU, the T-100 currently alloy radial turbine nozzle and turbine wheel. The alternate under development at the authors' company, will be used to designs are compared in terms of potential against such crite- investigate the feasibility of increasing the engine shaft power ria as performance, power density and cost. output by operating at higher turbine inlet temperature and I O UC IO shaft speed. Preliminary analysis of the engine performance indicated that the power output of the single-stage radial in- Future aircraft and armored vehicles will require more flow turbine can be practically doubled by operating at turbine secondary power with little or no allowance for a correspond- inlet temperatures in excess of 2000°F. Based on previous ing increase in size and weight of the power source: the small experience, two alternate design philosophies were selected, gas turbine Auxiliary Power Unit (APU). In addition to the high performance structural ceramic materials on the one hand high specific power output, the APU design criteria include and an air-cooled turbine nozzle in combination with a multi- such requirements as quick and reliable start, multi-fuel capa- alloy turbine wheel on the other. bility, self-sufficiency and high operational reliability while de- The final design and procurement of the test hardware is livering the optional electric and/or compressed air power un- in progress at the preparation of this paper. The design ap- der the most extreme environmental conditions of cold, heat, proaches and discussion of the two alternate designs are given humidity, dust and altitude. Past experience shows that these below.
ese e a e Gas u i e a Ae oe gi e Co g ess Ams e am, e e e a s— u e 6 , 88 .0
0.
S ( Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 0.8
0.
0.E 0 80 0 00 0 20 0 40 0 S ECI IC O SE OWE (s I S
IG . S ECI IC OWE A UE CO SUM IO AS U C IO O U I E I E EM E A U E A ESSU E A IO WI CO S A COM O E SI E. U A E 00 E GI E EC O OGY sections discuss background and experience with ceramic and EMO S A IO cooled radial turbine components at Sundstrand Turbomach.
The T-100 MPSPU is a gas turbine technology demon- IS O Y O CE AMIC EC O OGY O strator under development at Turbomach with sponsorship E O MA CE U A I G A U OMAC from the Aviation Applied Technology Directorate (AATD) of the U.S. Army Aviation Research & Technology Activity Uprating of small radial turbines using ceramic materials (AVSCOM). The MPSPU program will provide the technology began at Turbomach in 1972 with the testing of hot pressed base for small gas turbines in the 50 HP to 100 HP range, silicon nitride vanes the 100 HP Titan gas turbine (Ref. 1). compatible with applications in airborne or armored vehicle Although the primary intent of using ceramic vanes was im- auxiliary power units and mobile tactical shelter Integrated proved erosion resistance, the favorable high-temperature Power and Environmental Control Systems (IPECS). This pro- properties of ceramics offered the capability for increased TIT. gram involves a wide range of technology advances including In single-stage radial inflow turbines, the nozzle vanes--being improved aerodynamics for low specific fuel consumption, an exposed to the highest gas temperatures--are the prime candi- integral inlet particle separator, advanced combustor, digital dates for ceramic application. electronic control system with diagnostic capability and im- The early demonstration led to work on ceramic compo- proved durability, reliability and maintainability; all supporting nents for the Turbomach Gemini turbine shown in Figure 2. the concept of lower cost of ownership for Army users. The The Gemini is rated up to 45 SHP with single-stage rotor unit production cost goal for the baseline (50 HP) MPSPU speed of 93,800 RPM and turbine wheel diameter of 4.4 inches power module is approximately two-thirds of similar size (112 mm). Under a U.S. Army Mobility Equipment Research units. The durability goal includes capability to ingest three and Development Command sponsored research project, a full pounds each of 'C-Spec' and AC coarse sand with less than ceramic turbine nozzle was successfully tested for 200 hours 10% power loss. The reliability goal is 3000 hours minimum and 50 starts in a Gemini engine (Refs. 2, 3 & 4). Also, the mean time between removals (MTBR). erosion resistant ceramic vane Gemini nozzle concept was car- The uprated version of the T-100 MPSPU of nominal ried through a low-cost manufacturing feasibility demonstra- 100 SHP considered in this paper will be designed and demon- tion with qualification hardware completing over 2000 hours of strated along two parallel concepts: one using high-tempera- engine test (Refs. 5 & 6). (See Figure 3.) ture ceramic materials and the other with nozzle cooling in Demonstration of ceramic vanes, a full ceramic nozzle combination with an advanced tri-alloy metallic turbine wheel. (Figure 4) and all ceramic static components in the entire hot This effort will provide the unusual opportunity to evalu- section was followed by the design and testing of ceramic tur- ate and compare an advanced ceramic design and an advanced bine wheels in the Gemini engine in 1985 and early 1986. This metallic design throughout the development process. At this project was carried out as the first task of the internally funded writing, each of these schemes are in the preliminary analysis long-range Ceramic Technology Development Plan. and design stage. Each will be implemented as hardware and The T-20G10C ceramic Rotor No. 1 (Figure 5) was be carried through development tests. tested for 100 hours at 100 percent speed, 1800 ft/sec tip speed In order to provide a better perspective on the two tech- and full engine power output at a TIT of 1850°F (1010°C). nology options for uprating the T-100 MPSPU, the following Rotor No. 2 was subjected to cycling tests: 50 cold start cycles
2 turbine wheel into small pieces. The wheel burst was barely noticeable, characterized by a light thump and the loss of en- gine power. Hardware damage was limited to the turbine noz- zle. Examination of the turbine section after wheel burst clearly showed that the failure was completely contained and that containment can be easily accomplished with a ceramic wheel. The progression of ceramic hardware demonstrations in the Gemini engine is summarized in Figure 6. The results of Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 these tests have demonstrated the future potential of ceramic 4 components in small gas turbine engines and the need for im- proved materials, design and manufacturing methods. Current efforts at Sundstrand Turbomach are continuing for the design and testing of ceramic static and rotating compo- nents operating at temperatures in excess of 2000°F (1090°C). The ceramic technology development tasks include the devel- . r opment of new design and analytical techniques, nondestruc- tive and destructive material evaluation methods and the fabri- t n nd f r n n h rd r n l p r IG 2. U OMAC GEMI I GAS U I E tion with the suppliers of the ceramic parts.
EM E A U E U A E ME A A OY to full load in less than ten seconds were followed by 50 full A E A I ES load-no load cycles. After successful completion of the cy- cling tests, the rotor was subjected to an endurance test at full During the past 35 years, the intensive materials re- engine speed (93,800 RPM) and an estimated TIT of 1900°F search--primarily driven by the needs of the gas turbine indus- (1038°C). The rotor failed after completing 155 hours of op- try--has resulted in the development of numerous superalloys eration. Successive failure analysis showed carbon ingestion and a steady growth in their high-temperature capabilities. as the likely cause of the failure. An unauthorized switch in These improvements are reflected by the increase of turbine fuels from JP-4 to diesel fuel caused improper combustor/fuel inlet temperatures in uncooled small gas turbines over the matching and lead to excessive carbon formation in the com- years as shown on Figure 7. Most recently, the use of ad- bustor. v n d p r ll r lt d n p p r t n t p r t r t It was suspected that the pieces of carbon found missing 1830 to 1890°F (1000 to 1030°C). Although further improve- at several areas from the 1/2 inch to 3/4 inch-thick deposit ments are possible, it appears that the future growth in TIT for around the combustor wall have broken off and passed through uncooled metal alloy turbines will level off around 2000°F th t rb n , l d n f r t t th fr t r f th t rb n bl d (1090°C). Further increases will come slowly and may result tips followed by the total disintegration of the entire ceramic only from the application of cooling techniques.
CE AMIC I_ O E A E I I OM AI I G E GE COM US O O E O E A EA E EA I G E GE U I E I E CE AMIC A E
E>
COM ESSO U I E W EE W EE IG . CE AMIC A E O E
Si 4 A ES Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021
I
Aj . ( • t C
SiC S OU
IG 4. U CE AMIC GEMI I U I E O E A E 200 OU E GI E ES
4
Favoring the design effort are the maturity of cooling technology, availability of well-characterized materials, com- patibility of metals with the surrounding structure and designer familiarity with the materials. Cooled turbine technology is now an accepted practice and has been implemented in medium and large axial flow turbines. Over 20 years of design, production and operating experience with cooled turbines provides a wealth of data for Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 the successful application of air cooling in small gas turbine engines. Feasibility of fabricating small cooled radial rotors in the T-100 size range has been demonstrated (Refs. 9 & 10). In spite of the foregoing , the outlook for small radial turbine performance improvement with hardware cooling is not as optimistic as it might appear. Economic considerations and size effects complicate the task of supplying the above tech- nologies to the small turbine. The overall selling price of a small auxiliary power unit frequently cannot justify the cost increment for a nozzle vane cooling scheme, which may be appropriate to main propulsion engines. In fact, the small size IG . CE AMIC U I E O O of the unit further aggravates the situation because of added precision required in manufacture. For example, T-100 nozzle vanes include an internal cooling flow distributor which has YEAR U I G IME — OU S 0 00 000 passage sizes less than 0.010 inch diameter. Radial turbine stages, used dominantly in small turbomachinery because of hr C r n n zzl — 0 r — On St rt better single-stage performance, present inherent technical ob- 2 II stacles to cooling because of the large turbine shroud and tur- ft n C r n n zzl — 00 r — 00 St rt bine blading areas that must be cooled. Accommodation of the cooling airflow passages results in increased blade thick- ness and higher wheel mass, which penalizes engine perform- ll C r zzl — 0 r — 0 St rt ance and starting time. These problems are reflected by the current state of ra- dial turbine cooling which allows TITs only up to 2200°F ll C r zzl — 200 r — 0 St rt 80 (1200°C) for a relatively cost effective design (Ref. 7). At- tempts for higher allowable TITs result in designs which are C r n zzl — 2 0 r — 460 St rt economically impractical for most applications (Refs. 9, 10 & 84 11). In 1985 an advanced cooled radial turbine was developed C r rb n Wh l — 2 r — St rt 8 and tested at Turbomach. This radial turbine wheel employs a 86 complex cooling scheme shown in Figure 8. This design re- quires 13 percent of total inlet flow to reduce the maximum IG 6. CE AMIC COM O E EMO S A IO S I blade metal temperature below 1630°F (890°C) with 2450°F U OMAC A IA U I E E GI ES (1340°C) turbine rotor inlet relative temperature. The aerody- Temperature uprating of small radial metal turbines with namic penalties due to cooling flow reinjection were estimated cooled hardware presents a number of technical challenges for at 3.4 percentage points total-to-total isentropic efficiency for the gas turbine engineer. These include the design and analy- the turbine stage (Ref. 9). Further losses to the cycle due to sis of innovative cooling schemes which satisfy the following consumption of compressor flow would significantly compro- requirements: mise the benefits of higher TIT. The effects of nozzle cooling • Highly efficient utilization of the cooling air due to losses have not been considered and are not expected to be the small overall engine airflow. significant. • Blockage free (self-cleaning) passages for the cool- The combined effect of complexity and performance ing airflow in the relatively small hardware. penalties associated with a high-temperature cooled radial hot • Low manufacturing cost. section design limits the range of appropriate applications.
5 2200 20G 20C 200
2000 00 20G 0C i
S 220 Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 U A E GEMI I MA 24 000 62 46 800 U I E U I E I 2 I E I E EM E A U E EM E A U E 62 40 8 (° C (°C 00 600 62 2 ❑ U COO E ME A A OYS I CE AMICS 800 ❑ 62 2 400 A286
62 4 A286 00
200
0 60 0 80 0 2000 YEA O A ICA IO IG IS O Y O U I E I E EM E A U ES I U OMAC E GI ES E 00 CE AMIC A OAC The material characteristics of industrial ceramics are distinctly different from those of metallic superalloys, which the ceramics are intended to replace in gas turbine applica- tions. Ceramic parts are very brittle and contain randomly distributed flaws which result in high susceptibility to fracture. Structural strength and reliability of ceramic parts depends on the purity and the processing technology of the base material, the manufacturing method used to produce the part and — un- like metals — the physical size of the part. The unique proper- ties of ceramics require special design, analysis, manufacturing and quality control techniques, which differ significantly from those used for metallic materials. The structural strength of ceramic components is subject to statistical variation as described by the fracture strength dis- tribution model of Weibull. This is a direct result of the ex- treme brittleness (i.e., lack of ductility) of ceramic materials and the random distribution of microscopic flaws inherently present in ceramic parts produced with present processing techniques. Judicious characterization of ceramic material properties requires a careful review of the test specimen size, surface fin- ish and specimen origin from component as well as the test setup and methodology used to derive the material data. For example, the widely used methodology of characterizing the material strength by using the modulus of rupture could be misleading, especially for the low values of the Weibull IG. 8. COO I G OW SC EME O A A CE A IA modulus "m." Figure 9 shows the effect of "m" on the ratio U I E W EE ( E . of M.O.R./tensile strength.
6 2.00
.
A IO =
M.O. S E G Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 E SI E S E G .2
.00 4 8 2 6 20 24 WEI U MO U US
IG . WEI U MO U US " " S. A IO O M.O. . S E G I E SI E S E G
The structural analysis of ceramic parts includes the esti- mation of the failure probability using a fracture model and the statistical characterization of the material strength in the fast fracture and time dependent fracture modes. Unlike metals, the reliability of ceramic components with current manufactur- ing technology is strongly volume and surface dependent. The estimate of reliability requires a rigorous analysis for both vol- rs ume and surface flaws, based on the detailed knowledge of the stress distribution and the material fracture data (Ref. 13). The ceramic components currently under development at Sundstrand Turbomach include the turbine wheel, the turbine nozzle, the nozzle shroud and the heat shield. Figure 10 shows the ceramic parts assembled into the T-20G-20C engine test rig. This ceramic assembly is designed to operate with maxi- mum TIT of up to 2200°F. The components shown are esen- IG. 0. E GI E ES IG O CE AMIC U I E tialy the same design as those for the MPSPU T-100 uprated COM O E S engine. The silicon nitride radial inflow turbine wheel is sup- conditions. The steady state and transient thermal loads are ported from the cantilevered end of the shaft by a braze joint. based on the results of the finite difference thermal analysis. The shaft is made of a high—strength, high—temperature alloy Since the highest stresses are usually caused by the thermal with good corrosion resistance and low thermal expansion co- gradients, an accurate assessment of thermal stresses requires efficient. The braze joint is designed to transmit the wheel a detailed analysis of the time—dependent temperature and torque and the bending moments generated by the weight of stress distributions during engine starts, shutdowns and rapid the cantilevered wheel and the unbalance forces. load changes. The mechanical design of the ceramic rotor is based on The ceramic nozzle and shroud design is also based on the same structural design criteria that is used for the design of high—temperature grade silicon nitride material. This design the metallic turbine wheels. configuration represents a lower cost option to the all—ceramic The wheel has to survive the steady—state stresses gener- nozzle successfully tested in a 200—hour, 50—start engine test. ated by the rotational mass inertia load (C.F. loading) up to The vanes are integral with the inner shroud, which is located 125 percent of the design speed and the thermal stresses in- by three radial struts protruding into precision—machined slots duced by the wheel hub to blade tip thermal gradient at maxi- in the outer shroud. The outer shroud is centered through mum turbine power output. The wheel also has to survive the three slotted "ears" by axial guide pins from the compressor stresses generated during transient conditions such as a ten— diffuser. This arrangement provides for the centering of the second engine start to full speed and power as well as instanta- entire nozzle—shroud assembly without restricting the relative neous shutdowns. thermal growth between the individual components. The de- The structural analysis of the ceramic turbine wheel is sign includes a piston ring type seal at the exhaust end of the based on finite element techniques with mass inertia and ther- inner shroud, which is spring loaded axially to keep the assem- mal gradient loads applied at the steady—state and transient bly together. During engine operation, the pressure differential
7 will push the shroud against the end of the vanes, thus mini- mizing flow leakage within the nozzle.
E COO E 00 O E I A OY U I E W EE A OAC Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 The approach taken to increase TIT with a metal alloy construction includes an air-cooled nozzle and tri-alloy turbine wheels as shown in Figure 11. The air-cooled nozzle uses approximately two percent of compressor discharge flow for vane cooling. Secondary com- bustion air is provided for shroud temperature control. The turbine wheel employs three alloys to combine preferential properties at the hub and blade tip with an intermediate mate- rial providing the ability to achieve good bond integrity. The cooled nozzle concept incorporates internal impinge- SI G E ment cooling with trailing edge ejection. The key objectives of A 2 A C YS A this concept are to provide uniform temperature control of S A OY Y vane walls and to control the pressure balance from inside to outside of the vane for a "fail-safe" design. In the event of vane wall leakage, cooling air will exit the leak which precludes catastrophic deterioration. The design strives for simplicity in I 00 that it is a single-pass concept and a minimum number of vanes are used. This nozzle can be fabricated by conventional investment casting methods with fabricated impingement cool- IG . 00 M S U COO E O E A I A OY ing air distributors. U I E W EE The tri-alloy turbine wheel takes advantage of lower tem- peratures in a radial wheel provided by high single-stage ex- Analysis of the cooled nozzle design includes finite ele- pansion. The blade tips, which see the most severe stress-rup- ment heat transfer to determine vane and shroud temperature ture exposure due to highest temperatures, are made from Sin- profiles with the objective of minimizing thermal peaks and gle Crystal RSR (rapid solidification rate) Alloy "Y" material. thermal gradients to provide good stress rupture life. The This material offers exceptional creep life at 1600°F, which cooled nozzle stress analysis is similar to that of the ceramic occurs at the critical stress region with 2000°F TIT. The pow- nozzle, except that stress rupture is the criteria for evaluation der metal IN-100 fine-grain hub provides exceptional low-cy- as opposed to probability of failure for the ceramic. cle fatigue capability at maximum 1200°F hub temperature Tri-alloy wheel stress and temperature profiles are used and 100 KSI stress. to establish low cycle fatigue life at the hub section and stress The AF2-IDA powder metal intermediate alloy is ame- rupture life of the single crystal tips. Again, the stress analysis nable to the diffusion bonding process used in fabrication of is similar to that for the equivalent ceramic component, but this rotor and provides high bond strength with the single-crys- evaluation criteria involves low cycle fatigue at the hub instead tal RSR Alloy Y and IN-100. of probability of failure in fast fracture or slow fracture for the The tri-alloy wheel involves processing RSR Alloy Y into ceramic. Stress rupture of blade tips is critical for both RSR single crystal, either by solid-state directional recrystallization Alloy Y and Sintered silicon nitride. Silicon nitride stress rup- or by casting from a melt via directional solidification. The ture life will also include probability of failure as an additional Pratt & Whitney patented isothermal forging technique, known factor in this evaluation because of the brittle nature of ceram- as Gatorizing, is used to fabricate the tri-alloy rotor. ics. The tri-alloy turbine wheel offers advantages over the cooled turbine wheel shown in Figure 8. Its mass and rota- ESIG COM A ISO tional inertia are less (the same as conventional investment casting). No aerodynamic compromises, such an increased Comparison of the two approaches to a high-temperature blade thickness, are necessary for introducing cooling flow and uprated T-100 MPSPU power module can be made in terms of no cooling flow losses exist. these technologies as they exist today or in terms of technology advancements or improvements expected to occur in the near 1Pratt & Whitney Government Products Division is pro- future. viding the tri-alloy turbine wheel technology to the program as Important criteria in an evaluation include Specific Fuel a subcontracted team member. Consumption (SFC), specific power, weight, cost and life.
8 S eci ic ue Co sum io i e The comparison, in current terms, for lower SFC shows This is a critical issue in the design of a hot section com- the cycle penalties due to the metal alloy nozzle cooling flow to ponent. Both the metallic and ceramic high-temperature tech- be exceeded in the ceramic engine by ceramic turbine wheel nologies are expected to have the capability to meet life goals component efficiency reduction. As a result, the estimated for the T-100. Verification of this capability is the focus of SFC for the ceramic engine is higher. Turbine inlet tempera- development programs such as the T-100 MPSPU uprated en- ture of the ceramic uprated T-100 is projected to be higher gine program. This work is at too early a stage to accurately Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 than for the metallic cooled nozzle tri-alloy wheel design. compare component life of competing technologies. However, aerodynamic penalties to the ceramic wheel due to factors such as reduced blade count and thicker airfoils CO C USIO S only reflect design conservatism viewed as advisable at this The alternate paths of high-temperature structural ce- stage of development. ramics and high-temperature metal alloys with cooling or Indications are that continuing advances in ceramic rotor multi-alloy construction for increased TIT are diverse with re- fabrication capability and material strength and reliability will spect to design, design methods, manufacturing methods, capa- allow improvement in this area. bilities and limitations. Specific power and specific weight relate directly to these The metal alloy approach is, in general, more mature improvements in aerodynamics and component efficiency and, and, as a result, presents less risk in all areas. However, it is therefore, advances in ceramic materials will benefit these ar- also assured that advances will be limited and progress will eas also. proceed in small incremental steps. Ceramics offer an added benefit in weight reduction, not The ceramic path represents a high risk alternative with only in component weight, but in substantial start system much greater potential benefits to engine performance and the weight reduction due to reduction in rotating inertia with the potential for some cost saving. However, the development of ceramic rotor. It is estimated that start system weight reduc- the design, manufacturing and inspection methods will require tion equivalent to 17% of power unit weight could be achieved substantial investment. Successful completion of ceramic com- with a ceramic turbine wheel (Ref. 14). ponent demonstrations, such as discussed herein, may result in the use of ceramics in nonmission critical and unmanned small
Cos gas turbine applications during the first half of the 1990's. In the near term, particularly in a technology develop- The decision at the "fork of the road" may be guided by ment program, factors other than absolute performance must the above, given specific requirements for APU performance. be considered. Technical feasibility at a reasonable cost must However, the choice is not necessarily an easy one since nei- be given serious consideration. Each of the technology paths ther structural ceramics nor high-temperature metal alloy de- have been shown feasible throughout the industry, but cost signs can be realized without substantial development effort, within limits consistent with unit cost goals stated above, i.e., which will require major investment of resources. For cooled unit price at two-thirds of current equivalent engines, is more and multi-alloy metal components, manufacturing cost reduc- difficult to realize. tion is a must for practical implementation in APUs. Struc- A positive indication for ceramic component cost reduc- tural ceramics technology also has to improve substantially be- tion is the limited quantity commercial use of ceramic turbine fore the designer can have confidence in the structural integrity rotors in automotive turbochargers. This inferred low cost ca- of ceramic components. The evolution of reliable (tough) ce- pability has yet to be demonstrated for radial ceramic gas tur- ramic parts will require significant work in many areas from bine rotors which would see substantially less typical produc- materials development through hardware demonstrations. tion quantity than automotive turbochargers. (This is not to Due to the rapid development and lack of sufficient oper- suggest that these economies are not possible.) ating experience, no clear-cut choice exists at this time be- The ceramic radial turbine must also include the expense tween the two technology paths. increment for the nozzle which is not limited to the ceramic It is expected that the current work on the uprated T-100 component manufacturing cost alone, but includes the compli- NIPSPU, by exploring both alternatives, will provide some use- cation on numerous additional parts required to transition the ful comparisons and contribute to the development of the ceramic nozzle to its surrounding structure. structural ceramics and the metal alloy high-temperature APU Cooled metal and advanced tri-alloy wheel technologies technologies. offer more certainty in obtaining goals since these concepts do ACK OW E GME S not require advances in material properties in conjunction with a manufacturing process as ceramics must. However, the cur- The authors would like to recognize the contribution of rent term cost is not close to goals and this technology is not individuals at Sundstrand Turbomach, Pratt and Whitney Air- likely to advance as rapidly as ceramics. craft, and AATD to the uprated T-100 technical effort.
9 E E E CES 8 r , A., M ll , . . "C l n M d rn A r En n rb n l d nd n " SAE 6600 , n. 66 rd n, . ., t t "Appl t n f C r t d l Infl G rb n " SAE 0 42 r, A. ., t t "C p t C t n nd n C n 2 , .W. "An A nt f th U f C r n tr t n f n A r C l d, h p r t r d l t En n " p rt 44 rb n Wh l" 8 SAE 8
p r, .C. "Appl t n f All C r zzl t 0 r, A. ., " br t n f C l d d l rb n Downloaded from http://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT1988/79191/V002T04A010/2397688/v002t04a010-88-gt-228.pdf by guest on 28 September 2021 d l l rb n " ASME rn l f En n r n f r t r", ASA C 0 . r l. 02, . 2, Apr l 80 4 Arn ld, . ., t t " n tr t n f C r t S G.S. C lv rt, O. O p , " n nd Ev l t n f t n St t C p n nt n d l l rb n " h p r t r d l rb n " USAA A S ASME 82 G 84 hn l p rt 68 6 28 8 r tt & Wh tn A r r ft. Arn ld, . ., t t "M n f t r n M th d f r Er n t nt C r zzl f r S ll G rb n 2 M n n, S.S., " h r l Str nd C l t " ASME 82 G 60 M Gr ll 66 6 p r, .C., Arn ld, . . "Adv n nt n Appl t n f C r t th G n d l l G r G n , . ., "SCA E: A p tpr r r r t b n " ASME 8 G 8 MSC AS A f r l b l t An l f Str t r l C r C p n nt " ASME 86 G 4 , C., l , . . " n nd Ev l t n f h p r t r d l rb n th M v bl S d ll 4 C. d r , " r n G rb n A U " ASME zzl " SAE 8 8 82 8 G 24
I