1、,o w_ 84- 33 147NASA Contractor Report 172384Application of Stiffened CylinderAnalysis to ATP InteriorNoise StudiesE.G.Wilby and J.F.WilbyBolt Beranek and Newman Inc.Canoga Park, CA 91303Contract NAS1-16521August 1984N/ SANational Aeronautics andSpace AdministrationLangley Research CenterHampton, Vi
2、rginia 23665Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NASA Contractor Report 172384Application of Stiffened CylinderAnalysis to ATP InteriorNoise
3、StudiesE.G.Wilby and J.F.WilbyBolt Beranek and Newman Inc.Canoga Park, CA 91303Contract NAS1-16521August 1984NASANational Aeronautics andSpace AdministrationLangley Research CenterHampton, Virginia 23665Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,
4、-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TABLE OF CONTENTSSection1.0 INTRODUCTION 2.0 ANALYTICAL MODEL 22.1 Outline 2.2 Tone Transmission .2.3 Noise Reduction due to ReverberantField Excitation 2.4 Noise Reduction due to Boundary Layer orProg
5、ressive Wave Excitation Fields .2.5 Four Element Sidewall .2.5.1 Sidewall Transfer Matrix .2.5.2 Sidewall Stiffness 2.6 Loss Factor for Structure with Trim 2.7 Joint Acceptance for Fuselage Floor withReverberant Excitation .2.8 Joint Acceptance for Fuselage with ExteriorExcitation Field 2.8.1 Axial
6、Joint Acceptance for ReverberantField Excitation .2.8.2 Axial Joint Acceptance for Boundary Layeror Progressive Wave Excitation 2.8.3 Circumferential Joint Acceptance forReverberant Field Excitation .2.8.4 Circumferential Joint Acceptance forBoundary Layer Excitation 228I0I01212141720212222-i-Provid
7、ed by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SectionTABLE OF CONTENTS(Continued)Page3.0 SUMMARY OF METRO II TEST 3.1 Test Fuselage Structure 3.2 Test Floor Structure 3.3 Excitation .3.4 Interior Treatment .3.5 Test Configurations 4.0 ANALYTICAL REPRESEN
8、TATION OF METRO IITEST STRUCTURE .4.1 Fuselage Shell .4.2 Floor Structure 4.2.1 Attached Floor 4.2.2 Floating Floor Representation 4.3 Structural Modes 4.4 Measured Structural Modes .4.5 Structural Loss Factors 4.6 Floor Structural Modes used in theAnalytical Model 4.7 Sidewall Treatment . . .4.8 Ca
9、vity Model 4.8.1 Cavity Modes .4.8.2 Acoustic Loss Factors 5.0 ANALYTICAL REPRESENTATION OF METRO II TESTEXCITATION .242429293232353535353738385O585862626267-ii -Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SectionTABLE OF CONTENTS(Continued)Page6
10、.0 PREDICTED AND MEASURED NOISE REDUCTIONS FORMETRO II TEST . 757.0 EFFECT OF EXCITATION CHARACTERISTICS 897 89.1 General Aviation Propeller .7.2 Turbulent Boundary Layer 907.3 Comparison of Predicted Noise Reductions 967.4 Reverberant Field Excitation 1018.0 DISCUSSION AND CONCLUSIONS . 104REFERENC
11、ES . 108APPENDIX A - List of Symbols A-I-iii-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LIST OF FIGURESFigure Pagei 2.Be4.5.oB10.11.12.13.14.15.16.
12、17.Sidewall Trim: Insulation and Lining Cross-Section through Metro II Fuselage ShowingFloor Installation for Test 5 Details of Floor in Metro II Test Fuselage 5. Test Set-Up for Acoustic Tests on Metro II 5. Spatial Distribution of Sound Levels for Testson Metro II 5 . .Sections through Sidewall Tr
13、eatment for Testson Metro II 5 Absorption Coefficients Measured in TreatedMetro II Fuselage 5 .Structural Mode Shapes: Floating FloorConfiguration with Add-On Vinyl Measured Circumferential Mode Shape at 83 Hzfor Bare Fuselage Structure 5 Comparison of Measured Mode Shape with FuselageShell Model (N
14、o Floor) .Comparison of Measured Mode Shape with FloatingFloor Model (Rigid Joint) .Comparison of Measured Mode Shape with AttachedFloor Model (Rigid Joint) .Comparison of Measured Mode Shape with AttachedFloor Model (Hinged Joint) .Structural Loss Factors for Baseline Structure. . .Acoustic Mode Sh
15、apes (q = 0) Grid Used for Propeller Noise Predictions .Propeller and Fuselage Surface Point Geometry . . .ll25303031333345495152545557636869-iv-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-FigureLIST OF FIGURES(Contlnued)18.19.20.21.22.23.24.25.2
16、6.27.Predicted Noise Reductions for Metro II TestFuselage Exposed to Electropneumatic Excitation(Floor Treatment Transmission Loss = 0 dB) .Predicted Noise Reductions for Metro II TestFuselage Exposed to Electropneumatic Excitation(Floor Treatment Transmission Loss = 20 dB) . . Predicted Noise Reduc
17、tions for Metro II TestFuselage Exposed to Electropneumatic Excitation(Floor Treatment Transmission Loss = 400 dB) Predicted Trlm Factor (Sidewall Treatment Trans-mission Loss) For Metro II Test Treatments .Comparison of Measured and Predicted Noise Reduc-tions for Metro II Test Fuselage and Electro
18、-pneumatic Excitation (Different Assumed FloorTreatment Transmission Losses) .Measured and Predicted Noise Reductions forMetro II Test Configuration with Attached Floor(Configuration #7) .Comparison of Floor Vibration Levels With and With-out the Floor Attached to the Fuselage Frames E53 Measured E5
19、_ and Predicted Interior Sound Levelsfor Different Floor Mountings .Predicted Noise Reductions for Typical G.A. Propel-ler Noise Excitation (Metro II Test FuselageConfiguration #1) .Predicted Noise Reductions for Typical GeneralAviation Airplane Boundary Layer Excitation(Metro II Test Fuselage Confi
20、guration #1) .77787981828687_79q97-V-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-FigureLIST OF FIGURES(Continued)31.28. Comparison of Predicted Noise Reductions forDifferent Excitation Pressure Fields (Metro IITest Fuselage Configuration #1) 29.
21、Typical Longitudinal Distributions of ExcitationPressure Amplitude for G.A. Propeller and Simu-lated Propfan (Electropneumatic) Noise Sources. . .30. Comparison of Measured and Predicted Noise Reduc-tion for Reverberant Field Excitation (Metro IITest Fuselage Configuration I) .Comparison of Predicte
22、d Noise Reductions for Rever-berant Acoustic and Turbulent Boundary Layer Exci-tations (Metro II Test Fuselage Configuration #1,Floor Treatment Transmission Loss = 0 dB) .98100102103-vi-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSN
23、ot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LIST OF TABLESTable Pagei 5.6.7.I0.II.12.13.14.15.16.17.Outer Wall Structural Properties of Metro IITest Fuselage .Damping Values for Baseline (Bare) FuselageOuter Wall .Damping Values for Fuselage Structure with Vinyl
24、Sheet on Exterior .Interior Absorption Coefficients Test Configurations Structural Modes for Floating Floor Configuration .Structural Modes for Floating FLoor Configurationwith Add-On Vinyl .Structural Modes for Fixed Floor Configurationwith Add-On Vinyl .Average Structural Loss Factors for Fuselage
25、 Acoustical Properties of Sidewall Elements .Sidewall Resonance Frequencies .Acoustic Absorption Coefficients and Loss FactorsFor the Interior of the Treated Test Fuselage . . .Circumferential Variation of Free Field Pressure .Axial Variation of Free Field Pressure .Simulated Propeller Blocked Press
26、ure Amplitudeand Phase .Blocked Pressure Amplitude and Phase for GeneralAviation Propeller .Flight Conditions Associated with Boundary LayerEstimates .2627282834394143565961667O7O729195-vii-Provided by IHS Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by
27、 IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1.0 INTRODUCTIONThe transmission of propeller noise into an airplane fuselage hasa direct influence on the design of General Aviation and AdvancedTurboprop (ATP) aircraft. For this reason NASA has undertakensevera
28、l analytical or experimental studies which consider differ-ent aspects of the overall problem. In one analytical study1-4 a method was developed to predict sound levels in a stiff-ened cylindrical fuselage when the exterior of the fuselage wasexposed to a propeller noise field. The analytical model
29、wascompared with experimental results obtained from a small testcylinder. Under a separate investigation 5, noise transmissionmeasurements were made in the laboratory using the fuselage of aFairchild Metro II airplane. This experimental investigationprovided validation data for ATP noise control stu
30、dies.The present study has two objectives. The first is to adapt thestiffened cylinder analytical model 1-4 to the test conditionsassociated with the Metro II experiment 5 and to compare pre-dicted and measured results for the noise reduction provided bythe fuselage structure and treatment. The seco
31、nd objective is toextend the analytical model to include turbulent boundary layerexcitation so that comparative noise reduction predictions can beperformed for different types of excitation.The first part of this report (Section 2) describes theanalytical model I and the changes made to it in order
32、toaccomplish the objectives of the study. Section 3 presents anoutline of the Metro II test with emphasis being placed on theinformation relevant to the current study. Analytical represen-tations of the Metro II test structure and the test excitationfield are given in Sections 4 and 5. Then the pred
33、icted andmeasured noise reductions for the test fuselage are compared inSection 6. The effect of type of excitation on the noise reduc-tion is discussed in Section 7 and final conclusions are present-ed in Section 8.-I-Provided by IHSNot for ResaleNo reproduction or networking permitted without lice
34、nse from IHS-,-,-2.0 ANALYTICAL MODEL2.1 OutlineAn analytical model for aircraft interior noise prediction wasdeveloped under a program sponsored by NASA Langley ResearchCenter, (NASA Contract NAS1-15782), and is described in 1-4.The model calculates space-average sound pressure levels inside acylin
35、drical fuselage with a floor and sidewall treatment, whenthe exterior pressure field is generated by a propeller. Inaddition the model derives the noise reduction for an exteriorreverberant (diffuse) acoustic field.For this report, the analytical model has been extended to calcu-late the noise reduc
36、tion associated with turbulent boundary layerexcitation. In addition, the sidewall treatment has been modi-fied so that it may consist of 1 to 4 trim elements. Modifica-tions have also been made to the noise transmitted from the cabinfloor to the interior, to allow variation of the floor treatmenttr
37、ansmission loss.2.2 Tone TransmissionThe band-limited, space-average mean-square pressure in theinterior of the fuselage, for harmonic H at frequency _H isgiven by Equations (3), (8) and (10) in,_1. ,2If T_L is writtenTT_( IcolIin terms of its component parts, TMHL -_-_-_ j , then22 _ en A2_ (n,r)H
38、PlCol _._n r_i s,t - _-_ “mH 7-?_on “ M2mr “ _G(rH)1xi is essentially independent of area. ThusI revl_j $ (a_)wholecylinderrevj (6)cylinderabove floor-5-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-where _ = fuselage surface area= L.2wa (7)At = fu
39、selage surface area above floor: Transmitting area of fuselage with trim: L.2a(w- )O (8)This gives2jr2(_H)l = TtAt_ r2(_H) +Jinterior fuselageinteriorj rev Ir( H)floor (9)The reverberant field joint acceptance for the fuselage isdefined in Equations 62-73, Ref.l, and for the floor is definedin Secti
40、on 2.7 of this report. The value of the speed of sound,Coi, for the interior volume should be used.2.3 Noise Reduction due to Reverberant Field ExcitationFor a reverberant field, the exterior mean square pressures,t is related to the mean square blocked pressures,t incident on the fuselage bys,t = s
41、,t/2The noise reduction of the fuselage for the one-third octave bandat center frequency m is given by Equation 18 in Ref.l.Expanding the expression for TML gives-6-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 Ss,t2C4 _22Pl oIcJ 2revl2 A2_, 2Jr(
42、_)Jext“E En E M_D “n r r nr(n,r)c)+ n r in r2cn(br-bn) -bn(Cr-Cn) 1+ 4nn_ n arctann+ arctan r_(n r + n_. )_:rwhere _ is the fuselage surface area and A is the interior(cylinder + floor) coupling area.(I0)For n or r = J,in-j = In (l+ce/2)_e+b_(l+ce/2)2e2+col I (l-cm/2) _w_+b j (I-c_/2)2_2+cj Iarctanj
43、 = tan -I _tan -I J_nj_ L 4nj _j+ and when J = n, nj = _nwhere when J = r, nj above = _r _rAlso,= bnC -Dnr (Cr-Cn)2 + (bn-br)( r brCn) bn = -2_; br = -2_2rCn = _n (I + nn2) ; Cr = _r , + )_I + (qr nrThe expression for f(n,r), including the floor transmission lossis given in Equation (3), and the exp
44、ression for the exteriorreverberant field joint acceptance J_(a_)ext is given inEquations 62-73, Ref.l using the speed of sound, CoE , forthe exterior pressure field.-7-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-For high frequencies, when the ac
45、oustic modal density is high,the model was developed along the lines of 4,7,8. The powerabsorbed on the interior wall of the fuselage is given byEquation 22 of Reference I, assuming that the response isresonant acoustic. Structural modes resonant below the frequencyband (r = 4PICoI PE Col r ints,t r
46、eA_+ PE2weoErev - rev )r is used, rather than theexterior pressure , and the exterior field joint acceptanceJr (W) ext must be used in place of the reverberant fieldjoint acceptance in Equation (I0). This givess_ t plc _ _2_s;t _ n r r nr efJ_(m) ext A2_2(nr)X+ 2cn(br-bn) -bn(Cr-Cm)larctanC2 n4nn n(
47、12)+r arctanr ,_ )_2_(_r + _r rwhere the functions b,c,D, in are defined in Equation (i0). Theexterior field joint acceptance is defined in Section 2.8 forboundary layer and progressive wave excitation.Again for high frequencies, an expression similar to Equation(I0) is developed, and the noise reduction is given bys,t = 4PlcI+ PE2WCoE+ A 2 rev2P! CoE ._n int0E Co! r rcAmrA_ _Mr nt ext Plmnr4Coi_r /_ ef rev_r2Jr(U ) )ext “(_ “Jr(_)Jint_rcA_ rcA_4_CoI intrA_ “Jr ext-9-(3)Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,
