1、cc)-40coNATIONALADVISORYFOR AERONAtCOMMITTEEJTICSTECHNICAL NOTE 3422NOISE SURVEY OF A 10-FOOT FOUR.-BUDE TURBINE -DRIVENPROPELLER UNDER STATIC CONDITIONSBy Max C. KurbjunLangley Aeronautical LaboratoryLangley Field,Va.WashingtonJuly 1955Provided by IHSNot for ResaleNo reproduction or networking perm
2、itted without license from IHS-,-,-M TECH LIBRARY KAFB, NMNATIONAL ADVISORY COIMITTEE FOR AXRONAICS IllllllllllllilllllllllllllUllhLb55TECHNICAL NOTE 222NOISE SURVEY OF A 1O-FOOT FOUR-BIADE TURBINE-DRIVXNPROPEIUZR UNDER STAYIC ConditionsBy Msx C. KurbjunOverall sound-levelmeasurements and frequency
3、analyses of taperecordings of the noise emitted from a 10-foot-Maneter, four-bladepropeller mounted on a turbine-powered vehicle have been made understatic conditt.onsat stations eqyally spaced on a -foot-radius circle. The overall propeUer-noise pattern was unsymmetrical about the fuselagecenter li
4、ne, the maxtium sound-pressure level being located in the rightrear quadrant. The frequency analysis shows that this unsymmetrical dis-.tribution consists primarily of the two lowest propeller harmonics. hthe plane of and ahead of the propeller, hazlnonicsas high as the eleventh “are important.Theor
5、etical calculations of the sound-pressure levels by the methodof NACA TN 2968 predict accurately, for the 10-foot propeller investigated,the location of snd the maximum levels to be expected for the overall noiseand the first two propeller harmonics. The calculations do not predictaccurately the loc
6、ation of the maximum sound-pressure levels ad the maxi-mum calculated levels are 10 and 13 decibels lower than the msximm mess-ured levels for the third and fourth harmonics, respectively.The frequency szmlysis of the recordings obtained at several heightsabove the ground indicates the presence of a
7、 strong reflected wave orwaves, other than the ground-reflected wave, that reduced the sound levelat the ground as much as 6 decibels. The existence of this phenomenonand the unsymmetrical protuberances about the nose of the airplane whichreflect sound waves are possible explanations of the measured
8、 unsymmetricaldistribution about the rplane center lineINTRODUCTIONof the propeller noise.The atition industry is endeavoring to find ways of suppressing the. noise output of propeller- s jet-driven aircraft without limiting incertain areas the performancee and operation of these aircraft. rn thetic
9、inity of the airports, for example, noise emitted from aircraft on thekground and during take-offs and landings is of particular concern becauseof the high levels and the duration of the noise.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 3
10、4222gateResearch on propellers presents an excellent opportunity to investi- a71sound levels snd directional characteristicsof a number of proposedpropeller designs expected to be applicable to the high powers and high ospeeds of future airplanes. The 10-foot propeJJ-erinvestigated in thepresent rep
11、ort is typical of designs usedin todays aircraft and the tipMach number and-power loading investigated are representative of thoseused in current oerations. These results can be used as a basis forcomparison with the noise levels aud directionalproposed propeller designs.SYMBOLS “b blade width (chor
12、d),ftD propeller diameter, fth blade-section maximum thickness, ftR propeller tip radius, ftr radius to a blade element, ftcliaracteristicsof other. -.ably originate from thefuselage or wing. When the propeller is considered as a point source .with only a ground-reflectedwave and the free-spacewave,
13、 all harmonicsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 3422 7.should indicate a maxhum (6 decibels above free space) at the ground andraising the microphone through the range of heights to 5 feet should pro-duce no apparent change in s
14、ound level of the first harmonic, a decreaseof approximately 3 decibels for the second harmonic, a decrease of approxi-mately 6 decibels for the third harmonic, and a decrease of more than6 decibels for the fourth harmonic.The indication that multiyle reflected waves My account for vari-ation in the
15、 m?asured sound waves of the order of 6 decibels at onestation also suggests that this phenomenon snd the unsymmetricalpro-taibersmcesabout the nose of the airplane reflecting sound waves bethe cause of the masured unsymmstricel noise pattern.CONCLUDING REMARKSSound-level measurements and tape recor
16、dings of the noise emittedfrom a 10-foot-diameter, four-blade propeller have been made at stationsabout the propeller at a 75-foot radius. The tape recordings at eachstation have been analyzed to obtain overall sound-pressure levels andfrequency spectra.Overall sound-pressure levels obtained by dire
17、ct sound-level-meterreadings and from tape recordings agree within 3 decibels. The overallsound-pressure level displayed sn unsymmetrical distribution, the maxi-mm sound-pressure level in the right rear quadrant being 5 decibelshigher than the level in the left rear qyadrant.The distribution of the
18、sound-pressure levels of the first fourpropeller harmonics shows that the Unsymetricsl distribution 0$ noisein the rear quadrsnt is due primarily to an unsymmetrical.distributionof the level of the first two propeller harmonics. Higher harmonicsalso display en unsymmetrical distribution but the maxb
19、mrm levels inthe left rear qudrants are sufficiently low so as not to influence theoverall sound-level distribution. The frequency analyses show that thehighest levels of noise, behind the plane of the propeller, consist pri-marily of the lower propeller harmonics. lkLthe plane of and ahead oftke pr
20、opeller, however, harmonics ae high as the eleventh sms hrportant.The theoretical calculation by the method used b NACA TN 29 and as calculatedby thetheory of reference 1. Horsepower, 1,250; tip Mach number, 0.79.Provided by IHSNot for ResaleNo reproduction or networking permitted without license fr
21、om IHS-,-,-NACA TN X22.(a) First propeller harmonic (fundamental).Figure 5.- The sound-pressure levels at a 75-foot radius as obtainedthe anaJysis of the tape recordings and as calculated by the theoxof reference 1. Horsepower, 1,250; tip Mach number, 0.79.byYProvided by IHSNot for ResaleNo reproduc
22、tion or networking permitted without license from IHS-,-,-14 “NACAIN3422.(b) Second propeller harmonic.Figure .- Continued.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.NACA TN %22 15(c)!Ihirdpropeller harmonic.Figcme 5.- Continued.Provided by IHS
23、Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-16 NACA TN 34S.,(d) Fourth propeller hamnic.FUWe 5.- OU?led.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-JMNACA TN 3422 17./10%. /05g*e m23 95*$*850 / 45678 9 10 Ii
24、 12 /3 14XI02Frequenc cps (50 to 400)(a) Station 24& clockwise from nose.g /0.$ /05gg.looys 95$ 900 , s g5 6 7 8 9 10 II 12 13 14x102FrequencK CPS (50 to 1,400)(b) Station 259 clockwise from nose./095 A nn II II/(10095-Yo - u v850 / 2345678 9 10 II i2 13 14xl&frequenc cps (50 to (400)(.) Station 270
25、” clockwise from nose.Figure 6.- Vsriation of sound-pressure leve with frequency for a rangeof to l,kOO cycles per second ad a filter band width of 2Q cyclesper second. Fundamental blade passage frequency, 111.7 cycles persecond.Provided by IHSNot for ResaleNo reproduction or networking permitted wi
26、thout license from IHS-,-,-18 NAC!ATN 3422(d) Station 0 clockwise from nose.Fmquenc CPS (50 to I,40CJ(e) Station 330 clockwise from nose./00%95 A3? (90s! Aagm * ) . J$/fo -J *750 , 234 56789 fOli /2/3 IFmquenc cps (50 to 40Q)(f) Station O“ clockwise f+om nose.Figure 6.- Continued.- -.-$x/02Provided
27、by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 3h22 19Frequenccps (50 to L400)(g) StatiOn XCIOCMSefiom nose./151/0 II105 /f10095 1(90 J , ,22.FigureandSound levelo All frequenciesa75 - - - Isf harmonicot?dv -_dA _4fh“d-l I -n- a .+K- -0 / 2 3 4Distance above ground, ft8.- The effect of microphone distance above the ground on thefirst four propeller hszmmnic sound-pressurelevels. Station)II75.overall2700.NACA - Langiey Field, V&Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
