NASA NACA-TN-605-1937 Noise from propellers with symmetrical sections at zero blade angle《在零桨叶角时带有匀称截面螺旋桨的噪音》.pdf
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1、,9.,.-! :. “ .*.,!. ,m,.!.”,:;,.,a, “, ,. ”,.,” :“; “.-,L.J.iIJ:,:! ,.,.“,- ,.4“1,a71. WashingtonJuly1937Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.,.-31176013644928 _ .4“.,a71“-*.-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS-.-TECHNICAL NOTE NO
2、.-NOISE FROM PROPELLERS WITH605SYMMETRICALSECTIONS AT ZERO BLADE ANGLEBy A, F. DemingSUMMARYA theory has %een deduced for the iro$ationnoise!from a propeller tvithl)ladesof symmetrical section aboutthe chord line and set at zero blade angle. Owing to thelimitation of the theory, the equations give w
3、ithout ap-preciable error only the sound pressure for cases wherethe wave lengths are large compared with the blade lengthsWith the aid of experimental data o%tained from,atwo-%lade arrangement, an empirical Telation was intro-duced that permitted calculation of higher harmonics- Thegenerality of th
4、e final relation given is indicated bycomparison of measured and calculated sound pressure forthe fuildauental and second harmonic of a four-blade ar-rangement=INTRODUCTIONThe sulject of aircraft noitieis one u-fgreat com-plexity and may bedivided into many parts depending onthe various possille sou
5、nd sources involved. On the prac-tical,side the question-of reducing aircraft noise has,to date, teen largely one of insulation of ca%ins withlloundmrooflla%sor%ing materials. This remedy togetlierwith reduction of vi%ration has been very effective in re-ducing noise in aircraft cabins to levels now
6、 consideredtolera%le.The largest contributor to aircraft noises is thepropeller itself. The aircraft propeller is a very unusu-al type compared with ordinary sound generators. Compar -jatively little has been done toward analyzing the mechan+ism of the propeller as a source of sounds although a more
7、nearly complete analysis of propeller noise would be ofvalue, at lce,stfrom considerations of attempts to cur% orProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 N.A.C,A. Technical Note No. 605a71reduce the noise at the source rather than by its lat
8、erabsorption and reflection.Much of the published theoretical work on propellernoise is mentioned in a recent paper by Gutin (reference 2),which deals with the noise generfitedby a propeller owingto the creation of torque and thrust. !l!hepresent paperdeals with the effect of section or blade thickn
9、ess in re-gard to propeller noise and the theory is augmented hyexperimental data. It may be mentioned that the soundpressures calculated from Gutins relations did not checkthe values obtained %y measurements accomplished here ofpropellers operating under normal conditions of speed andthrust. Gutin!
10、s relation gives values for the fundamentalsound pressure of a two-blade propeller many times thosemeasured. His relation gives two comonents 180 out oftime phase with each other, whereas actually there existsanother component 90 tO either of these components.Eart (reference 2) presents some general
11、 considerationsand conceptions of the subject of noise from rotating ob-jeCtS. As Eartts paper does not include in any quanti-tative manner the consideration of thrust or torque, itmay perhaps le said tO apply rather closely to the subjectof the present discussion.Propeller noise may be classified i
12、nto the same twodivisions that hold for the noise generated by any revolv-ing object. This classification of IIvortexnoise?andIrrotati,onnoise!?was introduced in reference 3. Afterthis paper had been completed an artfcle on the same sub-ject appeared. (See reference 4.) Rotation noise for anormal pr
13、opeller is the more important of the two, underthe usual operating conditions of a propeller, because mostof the sound energy and odness (reference 5) is involvedin it, The vortex noise is due tO the shedding of vorticesfrom the propeller blades and manifests itself as a contin-uous acoustic spectru
14、m (on a timeeaverage basis). A StUiiyof vortex noise is given in reference 6. The rotationnoise is due to the revolving pressure field, or the waveenveopirlgthe blades, and is also possible of divisioninto two parts. one part is due to the production ofthrust: the other part-is duc to the thickness
15、of theblades displacing air in both directions perpendicular tothe path of the blades,The problem here is to evelop a solution for soundpressure of the fundamental and the first few harmonics Ofrotation noise at a distant point generated by a proeller.-.b.Provided by IHSNot for ResaleNo reproduction
16、 or networking permitted without license from IHS-,-,-M.A.C.A. Technical Note No. 605%. . . . -3b-b.with symmetrical-section, evenly spaced blades set atzero blade angle, and revolving at tip speeds below thatof sound. Such an arrangement will, of.course, produceno thrust since there is a symmetry a
17、bout the plane of ro-tation and no possibility of an angle of attack existingto produce a flow. The upper speed limit, as far as thispresentation is concerned, may be said to be determined %Ythe speed that produces local velocities equal to that ofsound aad it will, in general, bedetermined ly the t
18、hick-ness ratio and shape of the blade sectionsconsidered.This upper limit will, for most thickness ra,tiosand.streamline shapes used, be-about 0.7-0.8the velocity.ofsound.DERIVATION Ol?FoRMULASFigure 1 represents the.geometry of the pro%lem ofrotation noise generated by revolving symmetrical-sectio
19、nblades with zero blade angle. It is assumed in this paperthat the sound emanates from a narrow ring and that themovemeiltof the blades can be represented for purposes ofsound generation by an infinite number of ifinitesimalline pistons in this ring, each of which is given a phaseappropriate to its
20、position around the ring.“t=v-Iil figure 1, 0 is the center of the disk described IJYthe revolving blades. In plan view the axis of the %ladesis denoted %y the line All, the disk by COD; and theobservers position by P. In elevation view the axis isthrough O perpendicular to the paper: the disk is de
21、no-ed hy ACBD. The center of gravity of the elementarysources is descri%ed by the radius KR. The angle the ra-dius vector r (or 1) makes with the axis of rotation isP. It is seen that, as the angle Q is changed continu-ously, the distance from the observerat P changes peri-odically by the amount +x.
22、 It is assumed tha,t L islarge compared with R.For purpose of analysis let it %e assumed that thefundamental and first few harmonics of the rotation noiseemanate from a ring of mean radius KR. The area of thesources on one side of the disk would then bes =2Tr HKR2 (1)where H is a small quantity less
23、 than 1 and K, a quan-tity near to but less than 1. The quantity H may %eProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 N.A.C.A. Technical Note No. 605tfirmedthe lwidthllof the euivalent ring and is given asa fraction of the radius R.Since the bla
24、des are of symmetrical section about thechord, have zero blade angle, and operat in quiescentair, it is seen that a symmetry exists about the plane ofthe disk, It can therefore be assumed that only one-halfthe blade, or one side of the,chord, is operating and work-ing next to a wall of infinite exte
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