REPORT 1377 - CAFE Foundation

TABLE I.—R~ULTS wIT.H TAPERHD-BIAIIE PLAN-FORhI PROPELLE&Caoluded&.665D]Tat mndftiona &uud-preemre k-d, db(Reference prewlm led, 0.CM12 dynm/cm~Blad+ order of hfumonfmh!z T, lb ftr&c lb~~ ft “F :; QN& Mm Xz hi, ‘&wmquenoy, Id 2d 3d 4th Sth Wh 7thw8th 9th loth-O. 125D–. 126D–. 125D–. 123D–. 126D–. 126D–. 126D–. 125D–. 126D–. 126D–. 125D–. 126D–. 126D–. 125D–. 125D–. 125D–. 125Do0000:00:0000: %. 126D. 126D: E%: %. 126D. 126D: w. 126D126f): 12ilD~ g:1;24C90E01491491402492405451, :M74357560$6082, OH)2,0301, 100fK18916010016E+o640S707230528082, 1701, 2960009129220109128780;:EM06a076046ma0700660430360351, 11161,0141,0009909701, 0401,010960038Om970940040Etm000WJ38341, Ml1, Ui?:W6%3007006006694002,90160601,0101,026.1,0460009600600.22.3.5:;.60.EJ3.$.40.4049:49.49.::: ;:. ;:.33.#:60:%.H1.50.61.67.67.21.36. %. R.50.60: %.60.60.00.06.06—0.71.71.7J.08. H.74.74.70. %.71.71.70.70.77‘:;!.06.68.71.74. K.72.71.71: M. 7s.::60.71.73: ;;.71::: ;!.780.74.70.70.M.:.89.85.86.8-!3.861: %1.00L06.76: %.82.84: :;.91. %.87.87:8$L 02:2.;.02.02.03.85: %.94: 8;1.02FllghtM88.286.886.27Q. 582585.88a oMOE:86.886.986.386.186.386.603.52:E:8Z 3W. 68& 701.093.98& 68& 48E 88& a8& 303.586.3E:82.686.038, 7~~ o04.3E;67.1M. 384.780.304.31120107, 5Ioa 211(I 1111.6lla 7117, 0110, 6111.8110.9100.6112, 6115.1138.2134.5130.7117.6llii 7116.1{}$ :12ci 1122612(i 312& 3110.7119.3110.3127.7135, 2140.3116.8110, 0114, 6110.7119.3121.5122.8127.011117117.6117.5126.61320laL O130, 5104, 01020106, 61066115.0116.7106.9110.611X3. 5110.0120.7130.0133.6100.6loa 2109.0100.7110.3116, 0110.1125, 7127.21147lla 611’4.1126.4131.2131.0lCR. 2110.0104, 5Ioa o111.5ll& 6117.012* 7100.7Iom 810Q Q119.712fb o12E. 8124, 0loao114, 0106.3108, 6127.2127.3127.8[00. 3[00. 4[06. 7[12 b[la 9!24. 4.2& o.11.6.lfi 8.11.4.% o.27.0.!20 o,026o&506.806.010.0137.20.707.306.0oh ol& 22R o20.02h 6111.9(00. oL24 o[24 o[23, 8[02. oL04 o02.507.011.017.60360~ bIL 7’10.3lR 22& 81006121.0121.2[06. o[10. 5IIQ o.2a 7.Oh o.Oh b.17.0.10, 8.2h o04.00838;07.0lK 310.222610R1206llaoo[Oa o[17. 3~17. 6.o& o.Oil o.140.10.8.2$4.% ;IL 510.6I& 610,417.0Oii o14.0la ola 810.010.014.613 b17. bI/

TABI,13 11.—RII8ULTS WITH RINJTANCIULAR-BLADE PLAN-FORM PROPEIJLERS~=10.055D]Tukwndlliom~OrOnm~tiLY$,’?&d;ynw/Om~Ts T, lblTM. MZ M,Gram’Blnde- Ordcr of harmoniwP=quOnOy, 1St 2’ M .ith 6th Olh 7Lh 8kh M 10thCpstrots; 126D 2, &Jo o .- .-. . 00 1,030 2,705 0 0. g; a 07 8114 131.5 Izh 6 llao 111! o 11202, JJ30 o . . . . . . 00 1, 080 2, 700 0 07 8& 2 in. 6 1230 118.5 1130-. 125D 2, Mlo o ------ 60 1,030 & 700 0 :07 :07 8112 120.0 120.0 119.0 10EL o–O. 126D–. 125D–. 12Lm–. 121m–. 125D–. 126D–. MOD–. I!MD–. M8D_, l~Dn-!-11-b–0–o-o5-1Q107.0107, 6110.4120.0120.6104610I?L6121, 60, 126D. L2J5D. 123D. 126D. 126D. 1’MD. 125D1:10111s184365705111, 0121.6117.6131.012$6114.012* ollQ 5lza o1320117.01120124. b120.6119.5115.0120.5lzl. o113.0107.612$5123.0114, 5122012go127.0120.6la 5lza 6119.0124.5121.6125.0II

M3WS’URJID OSCILLATING PRESSUEEIS NEAR PILOPEIJZRS IN FLIGHT 1005EPFECTS OF FLIGHT MACH NUMBERThe effects of flight Mach number at the three axial microphonelocations are shown in iignre 4. A trend is shown forthe lower blade-passage harmonics of both blade designs todecrease slowly in sound-pressure level as the flight Machnumber increases to approximately 0.5 and to increaserapidly with further increase in ilight Mach number. Forthe lower blade-passage harmonics the tapered blade showswlower sound-pressure level than the rectangular blade.The higher harmonics show a slight increase in soundpressurelevel for both blade designs up to Ill.= 0.5 withrapid increases for higher fight Mach numbers. AboveMw=0.5 the tapered-blade design shows a more rapid increasein sound-pressure level with Mach number than therectangular-blade design. This trend, which is more pronouncedfor the higher harmonics, produces higher soundpressurelevelsin the higher harmonic range for the taperedbladedesign than for the rectangular-blade design.EFFECT%OF ENGINE SPEED (ROTAmONAL MACH NUMBER)The effects of changing the engine speed (rotational Machnumber) on the sound-pressure levels at a constant forwardMach number and power are shown in figures 5 and 6 for thetapered- and rectanguhwblade designs, respectively. Theresults for both blade designs show small increases in theoscillating pressures with rotational Mach number for thetit harmonic, but the increase for the higher harmonicsbecomes increasingly greater.03[30120110la)130120 —x.- b.125 DIIc —— __ --- &------ _ __4_-w--I I I I I I I(110 0 2700 .86 —QA 2800 .88\ ‘4 %C. 2900 .90 \ +DW30 .921004o&80 [~ 200 400 EOo 800 ]~Frequency, CPS~GURH 5.—Variation of sound-p~ure Ievek with engine speed forthe tapered-blade propeller. Blad&passage harmonioa are conneotedwith dashed lines for identiiioation purposes only. l.f~ =0.5;P s1,000 hp;~=().f355~.150e rpm M,o 2497 0.84140 n 2597 .860 2712 .883 A 2893 .92~ 2940 .93“$-130%_.y-s!;[ n&140‘eHi-——, I! =Q125L7b — +.--L l.=-- —- – F “ -+ % ‘%HIIoq I I I I I I I I I I I I I I I IJ 23 .4 .5 6 7 BFlight Mach number, MmFIGURE A.—Variation of propeller noim’ harmonio content with tighthfaoh number. i’f =2,700 rpm; P= 1,000 hp; &= O.6651).i& .;120 ( .+ P>_.+. “*..2\\\ %G,:, :=*\\;110 “ ..-=3% ‘2 ‘ ~‘-w ‘h \h10040 Go80 ]@ 200 400 600 aoa .. IrFrequawy, cpsFIGURE 6.—Variation of sound-praw.ure levels with engine speed forthe rectanguhm-bide propeller. Blade+pwage harmonim are conneotedwith daahed linM for identification purposes only. ilf= =0.5;P =1,060 hp; microphone Ioeation, x= –0.1261).Figures 7 (a) and 7 (b) show that the effects of flight Machnumber are similar to those of rotational Mach number.Data for @we 7 (a) were obtained at a flight Mach numberof approximately 0.5 and an engine speed of 2,900 rpm.Data for @ure 7 (b) were obtained at a flight Mach numberxl

. ..— ..-— ....._. — .._= _ — —.—. — . . .1006 REPORT 1377—NATIONAL ADVISORYcOMMITTEDFOR AERONAUTICSlx)1401?0 # - —120* - —--.\- -Y. L0--—I10-x TcIr Rec}fng.hr ‘‘y \3_.!=0.125D o 0:100 (a) on u5 -o. 25D 0 u:150L%+$140130 L -+.~ ~===&: ~.’=. .“Y. ~~ “%,120L -—-_‘-a+‘- -h%. :t, “

MEASURED OSCIIJATING PRESSURES NEAR PROPEIXERS IN FLIGHT 1007obtained allow a few broad generalizations to be made.which are as follows:(1) In agreement with the theoretical results of reference 4,the results of the present investigation, as shown in figure 4,show rm initial gradual decrease in the oscillating pressureswith a more rapid increase at flight lMachnumbers above 0.5.This was also shown in the results of reference 7, whichutilizes the theory of referen”ie 4. When account is takenof the diilerences between the flight-test configuration andthe contlgumtion emm.ined theoretically in references 4 and7, the pressurelevels and changes in level with Mach numberare also in rather satisfactory agreement.(2) In rgreement with the theory of reference 4, the testresults show that the level of the higher harmonics of thepropeller noise increases at a higher rate than that of thelower harmonica with increase in flight Mach number. Thistrend is shown in figure 5 of reference 8. The calculationsof reference 8 utilize the theory of reference 4.(3) For the propeller studied in reference 4, the oscillatingpressuresin the plane of the propeller disk and ahead of thedisk were “found to be lower than those immediately behindthe disk. This theoretical result is contrary to the resultsfound in the present tests, as is shown in figures 5 to 8.This contradiction does not, however, invalidate the theory.Rather it indicates that other effects such as variation intorque and thrust distribution should be investigated. Asnoted in the previous section, the outer portion of the bladeswws operating under unloaded condition for forward Machnumbers above 0.5.CONCLUSIONSAs part of a brief flight program initiated to check thetheory of Garrick and Watkins @TACA Rep. 1198), a brief.set of measurements were made of the oscillating pressuresin the vicinity of a blade of tapered plan form and a bladeof rectangular plan form at flight Mach numbers up to 0.72.Measurements were made at a single radial station and atpositions ahead of, in the plane of, and behind the propellerdisk. The scope of the tests was found to be insuilicient toobtain complete verification of the theory for the effect offorward speed on the sound-pressure field around propellers,but it was possible to substantiate the following two phenomena:(a) The oscillating pressures near the tips of a propellertend to decrease slowly with increase in flight Mach mpnberup to a Mach number of approximately 0.5 and then toincrease rather rapidly at higher Mach numbers.(b) The sound-pressure levels of the higher harmonics ofthe propellar noise increase at a higher rate with increase inflight Mach number than do the lower propeller harmonics.In contradiction to the results found for the propellerstudied in NTACARep. 1198, the oscillating pressures in theplane of and ahead of the propellers of the present investigationwere found to be higher than those immediately behindthe propeller. Factors such as variations in torque andthrust distributions, since the blades in the present investigationwere operating above their design forward speed, mayaccount for this contradiction.The effect of blade plan form shows that a tapered-bladeplan-form propeller will produce lower sound-pressure levelsthan a rectangular-blade plan-form propeller for the lowblade-passage harmonics (the frequencies where structuralconsiderations are important) and will produce higher soundpres-surelevels for the higher blade-passage harmonics(frequencies where passenger comfort is important).LANGLEY AERONAUTICAL LABORATORY,NATIONAL ADVISORY COWWCEE FOR AERONAUTICS,LANGLEY FIELD, VA., July 1, 1968.1. Gutin,L.: On the SoundField of a Rotating Propeller. NACAThf 1195, 1948.2. Hubbard, Harvey H., and Regier, Arthur A.: Free-Space OsculatingPressures hTenrthe Tips of Rotating Propellers. hTACA Rep. 996,1960. (Supemedes NACA TN 1870.)3. Vogeley, A. W.: Sound-Level Measurements of a Light Airplanehlodifled to Reduce Noise Reaohing the Ground. NACA Rep.926, 1949. (Supersedes NACA TN 1647.)4, Gmrick, I. E., and Watkins, Charles E.: A Theoretical Study of theEffeot of Forward Speed on the Free-Space Sound-Prwure FieldAround Propellers. hTACA Rep. 1198,1954. (SupermxiesNACATN 3018.)REFERENCES5. Mace, WilIiam D., Haney, Franois J., and Brummer, Edmund A.:Instrumentation for Measurement of Free-Space Sound Pressuresin the Immediate Vicinity of a Propeller in Flight. NACA ThT353% 1966.6. Arnoldi, Robert A.: Near-Field Computations of Propeller BladeThioknem Noise. Rep. R-0896-2, United Aircraft Corp., Res.Dept., Aug. 30, 1956.7. Itagier, Arthur A.: Why Do Airplanes Make hToise? SAE PreprintNo. 284, SAE Nat. Aeronautic Meeting (New York), Apr. 12-15,1954.8. Sohmey, Joern, and C1ark, W. H.: Turboprop Propeller NoiseNeedn’t Be a Bugaboo. SAE Journal, vol. 62, no. 4, Apr. 195%pp. 44-47.

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