Jul 16 .974 Abstract
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A THERETICAL AND EXPERT1'MNT INVE7STIGATTON 0'P THE "DERFORMANCE O7 7T,APPED TTThDERS by Bohdan W. Orrnenheim Undergraduate Diploma, Warsaw 7olvtechnic, Poland, 1970 M.S., Stevens Institute of Technology, 1973 A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Naval Architect at the MASSACHUSETTS TNSTITUTE OF TECHNOLOGY May, 1974 Signature of the Author: Denjrtment of Ocean Engineering, M1av, 1P74 Certified By: Thesis Supervisor Accepted By : ARCHIVE9 Chaman, Dent. Comm ttee on Graduate Students JUL 16 .974 ABSTRACT Two flapped rudders with .10 and .20 flao areas of a typical high speed vessel were examined exnerimentally in a water tunnel, in free stream, and behind a oroneller. Effects of rudder geo- metry are discussed in detail, in particular, effects of taner ration, thickness, sween angle, and flan size. A lifting surface nrogram was written and used in order to compare and choose the best rudder planform. Pesults include free-stream coefficients of lift, drag, moment and flan moment, for a wide range of angles of attack and flan deflection angles. Effects of variations in nropeller-rudder axial clearance was ex- amined. Presented is a discussion of effects caused by viscosity, gans,and wall interaction. Comnarison was made with the nerform- ance of other flapped rudders. A rudder with 20. flan was selec- ted as one having the best performance characteristics. A strong effect of rropeller wake on rudder characteristics was observed. TndeDendence of rudder forces on axial clearance between propeller and rudder was noticed. CON TmENTS 1. Introduction ............... 1 2. Rudder Shape ............... 3 3. Design of Test Equipment ... 17 4. Accuracy of Measurements and Data Reduc tion .............. 53. Range of Parameters measured 32 6. Results and conclusions .... 33 7. Comparison of Theoretical and Exrerimen .a1 Data . ....................... ........... Acknowledgement ............ ........... 61 0. Nomenclature ............... ........... 63 10. References ................. ........... 11. List of Figures and Tables . ........... 66 12. Appendix (Lifting Surface Program) 1. INTRODUCTION Flaps have long been recognized and apolied in aerodynamics to increase the lifting characteristics of control surfaces. But prior to 1972, there appeared to be very little systematic data available on flaped control surfaces, with aspect ratios suitable for ships. In 1968-1972, a project was carried out at MIT, to provide the beginning of a systematic series of experiments yielding flapped rudder data of direct use to the designer (1). It was an experiment which determined the free stream characteristics of a series of twelve rudders with systematic variations in the amount of flan area and flao balance. Shapes of rudders were tvnical of a high sneed vessel. Asoect ratio was chosen rather arbitratelv to be 1.4. Flap size varied from 20% to 60% of the total project- ed rudder area, and balance - (defined as the distance the hinge line was moved aft of the center of circular radius flan leading edge as a percentage of the nominal flap chord) - from 0 to 10%. Among other interesting results of that investigation, it was observed that the 201 flan, no balance all-movable rudder, had the best characteristics. It was also concluded that balan- ced flaps produce disadvantageous flow effects. This information aroused a speculation that nerhans an all- movable rudder with a smaller than 20Y flap, of zero balance, would be more beneficial. The objective of the nresent work was to obtain the steady -l- force coefficients acting on a 10 flap rudder in free stream, as well as behind a propeller for different propeller-rudder con- figurations, namely for single screw-single rudder, double screw- single rudder, and double screw-double rudder of a tyrnical high speed vessel. -2- 2. Rudder Shane The initial idea was to nreserve the rudder shane from the series (1), decreasing only the flan area to 105 by moving the flan hinge axis towards the trailing edge; and, if needed, scal- ing the model size to suit the geometrical reouirements of mutual nronortions of the tunnel test section, and nroneller and rudder sizes. The first difficulty encountered during this attemnt, was that the hinge line of the 10 flan, (which was arbitrarely con- strained to be nerpendicular to the root and tin sections), would intersect the rudder tin so far aft that the thickness of the tin was too small to allow installation of any bearing of renuired strength. Several solutions were possible: to increase the rudder sween angle, thus moving the tin section aft relative to the root section, so that the ratio of the flan chord to the tin chord would be much larger at the tin than at the root , or to increase the basic thickness of the tip section, or finally to increase the taner ratio (ratio of the tin chord to the root chord); or to apply all these changes simultaneously In some suitable way. Here a matter of ontimization Of these narameters became of prime imnortance. Decision at the thickness change was based on the exnerience from the original experiments (1). Those rudders tapered from a root thickness ratio of 0.? to a tin thickness ratio of 0.1 following -3- typical Practice. However, one of the reasons given in (1) for the poor maximum lift coefficient of the rudders comnared for example, to the Whicher-Pehlner data (14) is that the latter has a uniform thickness ratio of 0.15. 'or this reason, it was de- cided to adopt a uniform thickness ratio of O.15 over the whole rudder span. Asnect ratio, it was decided, would remain the same as in the original rudders, namely 1.4. The remaining values to be determined were the sweep angle of the auarter chord line, and taner ratio. Asnect ratio of 1.4 is too low for lifting line theory anoli- cation and too high for low asnect ratio theory. Tn view of the lack of any analytical solution for ontimization of sween angle and taner ratio values, a lifting surface Program was written (2). The listings of this program is included in the Appendix. This is a rather general computer program for numerical evaluation of lift slope, induced drag, rudder efficiency, moment coefficients, and position of the center of Pressure for any flapped rudder tra.erzoidalola form, with a constraint that the hinge line does not intersect leading or trailing edges, and is nernendicular to the root and tin sections. Characteristics of rudders without flaps can also be obtained by snecifying in the innut, a dummy flap area, subject to the above constraint. Solutions for several nlanforms with systematic variations in sweep angle and taper ratio were obtained using this nrogram. Pinal choice of these narameters was based on three values that appear in the output: lift slone coefficient, induced drag coefficient, and rudder efficiencv. An additional condition that had to be satisfied was that the hinge line had to intersect the tin section far enough forward, so that at this point the tin section of assumed thickness would be thick enough to nermit in- stallation of hinge details of sufficient strength. The ontimum sweep angle came out to be 170 aft, comnared to 110 aft used with the series (1). The optimum taner ratio came out to be, coinci- dentally, identical with that of' the original series, namely 0.60.. (Figure 1). Purthermore, the combination of a taner ratio of' 0.60 and a sween angle of 150 of the ouarter chord, resulted in the trailing edge of the rudder being nernendicular to the root and tin chords. Since the flan hinge is 'also normal tOLthe root chord, significant simplification in the geometry of the flan was made nossible. This is described in the following chanter. Since the nlanform of the 1% flan rudder had been changed from the original rudders, and one of the objective of the nresent nroject was to comnare this rudder with the 20l flap rudder, another model had to be built, namely one with a 201 flan, and the same planform as the 10"' flan rudder. Tt was also intended to test one rudder without a flan, and such a rudder could be ma.d.e of one of the above, by filling the gap between the skeg and the flap with a filler. Span length was determined from geometrical considera- tions of mutual proportions, between the rudder and the nroneller, as well as of the tunnel test section blockage limitations. Tvi- cal values of the clearance between the ship hull and the nro- peller circumference is 0.3 of the propeller diamter D. Rudder tip is usually 0.25D above the lowest point of the proneller cir- cumference. With the nroneller of the diameter 7.4p" selected for these tests, the rudder span came out to be 7.P75". (Pigure 1). The sectional shape of the 66 series (5) was selected for the original tests, because its maximum thickness is well aft of the leading edge, which was desirable for large flan rudders. Since no large flap rudders are included in the current nroject, this constraint no longer applies. The 63 series shape was therefore selected for the current series, because it should have a larger stall angle and higher maximum lift than the 66 series. The 632~ A015 sections have, however, been slightly altered in order to develop a plain two-dimensional prismatic flan, and flan gap. This permits the flap section to consist only of a circular arc leading edge, and straight lines emanating from the tangency noints of the leading edge to the sharp trailing edge, with a selected edge thickness of 0.020". The flap gap was chosen to be very small, namely 0.010", in order to minimize the flow through it, inasmuch as such cross flow decreases the pressure jumn across the hydrofoil, thus reducinp 7.031-73 +-0.