Chen, Zhenhua

Gao, Qiang

Wen, Chunhua

Zhu, Binsheng

English

Purdue E-Pubs

Purdue UniversityPurdue e-PubsInternational Compressor Engineering Conference School of Mechanical Engineering2008Analysis of Acoustic Characteristics ofAccumulator of Rotary CompressorBinsheng ZhuGuangdong Meizhi Compressor Co. Ltd.Qiang GaoGuangdong Meizhi Compressor Co. Ltd.Zhenhua ChenGuangdong Meizhi Compressor Co. Ltd.Chunhua WenGuangdong Meizhi Compressor Co. Ltd.Follow this and additional works at: https://docs.lib.purdue.edu/icecThis document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu foradditional information.Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/Herrick/Events/orderlit.htmlZhu, Binsheng; Gao, Qiang; Chen, Zhenhua; and Wen, Chunhua, "Analysis of Acoustic Characteristics of Accumulator of RotaryCompressor" (2008). International Compressor Engineering Conference. Paper 1856.https://docs.lib.purdue.edu/icec/18561207, Page 1 Analysis of Acoustic Characteristics of Accumulatorof Rotary CompressorBinsheng Zhu1*, Qiang Gao2, Zhenhua Chen3, Chunhua Wen41R&D Section,Guangdong Meizhi Compressor Co. Ltd., Guangdong,P.R.ChinaTel:86-757-22329411,Fax:86-757-22297554,E-mail:zhubs@chinagmcc.com2R&D Section,Guangdong Meizhi Compressor Co. Ltd., Guangdong,P.R.ChinaTel:86-757-22329422,Fax:86-757-22297554,E-mail:gaoq@chinagmcc.com3R&D Section,Guangdong Meizhi Compressor Co. Ltd., Guangdong,P.R.ChinaTel:86-757-22329419,Fax:86-757-22297554,E-mail:chenzhenhua@chinagmcc.com4Test Section,Guangdong Meizhi Compressor Co. Ltd., Guangdong,P.R.ChinaTel:86-757-22329053,Fax:86-757-22297554,E-mail:wenchunhua@chinagmcc.comABSTRACTSince the accumulator is one of the most important component with the largest sound radiation surface area in rotarycompressor,its noise contribution may be substantial.Noise generation and transfer mechanism of the accumulatorare so complicated that it is difficult to identify the acoustic characteristics,because both structural and cavity modalare possible to be excited by many sources such as structural vibration,aero-acoustics,pressure pulsation etc.,inaddition coupling between them cannot be ignored either.In this paper,both of the noise generation and transfermechanism are studied systematically,also standing wave and mechanical vibration theory are applied to build themathematical model. To clarify the natural characteristics of the accumulator,both structural modal experiment andcavity modal simulation approach are applied by using commercial software Test.Lab and SYSNOISErespectively.Finally the structural modification experiment are carried out and proved that the model and simulationin this paper are reliable enough,it shows that both overall noise level and sound quality are improved,especiallynoise level was reduced about 10 dB(A) at few special frequency band.1. INTRODUCTION Usually accumulator of rotary compressor is connected with main case by a holder and suction pipe B,as is shown inFigure 1,both vibro- and aero- acoustics can be excited by many sources such asmain case vibration,pressure pulsation,gas flow and evaporation of liquidrefrigerant,finally it is radiated out via the vibration of the accumulator shell no matter whatever the noise source is.Many studies were done on accumulatornoise by foreign experts,Kim et al.(1998) used structural modal analysisapproach to eliminate the abnormal noise peak near 2kHz[1],Zhou et al.(1998) simulated the noise level radiated from accumulator shell due to internalpressure pulsation by FEM and BEM numerical approach[2], Wang et al.(2002)modified the accumulator rigid modes to improve the compressor noise level bytopology optimization techniques[3].While up to now we still haven’t seen anypaper about the accumulator noise due to coupling of structural and cavitymodes yet,its mechanism and acoustic characteristics was discussedsystematically in this paper combining theory,modal experiment and simulationapproach, afterwards it’s validated by noise experiments.Figure 1:Accumulator connectionPipe BHolderAccum.2. MATHEMATIC MODELWhile building the mathematic model of accumulator, we simplified it is a rigid long pipe with two closed end  as is International Compressor Engineering Conference at Purdue, July 14-17, 20081207, Page 2 shown in Figure 2,where pipe length is l,left end x=0 and right end x=l,also we assume that dimension of pipediameterφd is much more smaller than sound wavelength  what we are concerned about,so only plane wavesparallel to the pipe axis can be propagated in the pipe.If incident sound wave pi(x,t) which transmits from left toright equal to p0sin(2 ft-k(l-x)),where p0 is sound pressure amplitude, f is sound pressure frequency, k iswavenumber,and k=2 / ,corresponding particle velocity of incident wave ui= pi(x,t)/ 0c,where 0 is mediumdensity,C is sound velocity. According to transfer characteristics of sound wave,incidence wave will cause areflection wave pr(x,t) =p0sin(2 ft+k(l-x)) which transmits from right to left with the same amplitude after it reachesthe right rigid end,corresponding particle velocity of reflection wave ur=-pr(x,t)/ 0c,according to the theory of soundwave superposition,the sound pressure p(x,t) anywhere in the pipe is given as below,xlkftpxlkftptxptxptxp ri 2sin2sin,,, 00                                                                               ftxlkp 2sincos2 0         (1) Equation(1) shows that its amplitude 2p0cosk(l-x) is a fuction ofsingle variable x,independent of variable t,it means that a “standingwave” is formed in the pipe due to the superposition of incident andreflection wave.When cosk(l-x)=0, amplitude is always equal tozero,normally we call this position wave notch,when cosk(l-x)=1, amplitude is always equal to 2p0, we call this position wave，crest obviously sound wave “stay” in the pipe into a stable state.  In Figure 2: Accumulator mathematic modelthe same way particle velocity u(x,t) can be given as below,ctxptxptxutxutxu riri0,,,,,                       cxlkftpxlkftp000 2sin2sin                                                                    cftxlkp00 2cossin2                                                                     (2)There is no doubt particle velocity u(x,t) 0 while x=0 and x=l due to the assumption of rigid boundary condition inboth end,if we want to let sinkl 0,k must be some specific value given as below,                                                           lnk  ornl2       n=1,2,3…                                                              (3) Furthermore we can get the standing wave frequency fn=c/ =nc/2l ,that is also the modal Frequency which modalshape is axial standing wave.Discussion above is based on the assumption of dimension of pipe diameter φd is much more smaller than sound wavelength  and only plane waves parallel to the pipe axis can be propagated in the pipe,actually there are high-order cavity modes exist due to dimension of pipe diameter is not always smallenough.At the same time,accumulator also has a series of part and rigid structural modes because it is a thin-walled structure attached to main case,noise peak is possible to occure because of resonance if cavity modes couple with some structural modes and its frequency are closed to the vibration or noise frequency of  the main case.3. SOUND SOURCE IDENTIFICATIONWe choose the simplest separation method to identify the noisecontribution of the accumulator,pipe B is extended and accumulatoris placed outside the semianechoic room,basically we can achieve thepurpose of removal of  accumulator noise by this way.Thecompressor sound power spectrum before and after the separation ofthe accumulator are compared as is shown in Figure 3,from theresults it is found that the noise contribution frequency of  theaccumulator in this case mainly focus on band 400,500Hz and1250Hz,especially at band 400,500Hz more than 10dB(A)exceeded,so the studies below we focus on cavity and structural modes which frequency is close to band 400,500Hz and 1250Hz.28.18 17782.7950 63 80 125 200 315 500 800 1250 2000 3150 5000Octave 1/3Hz0701020304050601525354555dB(A)W0.0070.00dB WA L400500125066.765.0Curve 400 500 1250 Hz53 53 61 W39 42 58 WAfterBefore Figure 3: Noise spectrum comparison before and after separation of the accumulatorInternational Compressor Engineering Conference at Purdue, July 14-17, 20081207, Page 3 4. CAVITY MODAL ANALYSISWe simulate accumulator cavity modes using acoustic FEM approach by commercial software SYSNOISE, parameters density  and sound velocity C are chosed according actual situation, both ends of  the accumulator areset to rigid boundary condition, the first 10 simulated modal frequency are shown in table 1, it shows that the 2nd, 7thTable 1: Simulated cavity modal frequencyModal number 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10thModal frequency(Hz) 188 427 566 824 940 1147 1259 1260 1376 1376Figure 4: The 2nd cavity modal shape    Figure 5: The 7th cavity modal shapeand 8th modal frequency are very closed to band 400,500Hzand 1250Hz respectively which we are concernedabout.Their modal shapes are shown in Figure 4,5,6respectively, obviously these three modal shapes are allmain body vibration of  the accumulator cavity,and the 2ndis low-order axial mode,the 7th and 8th are high-order radialmodes,the result matches the former theory analysis,also the7th and 8th modal shapes are similar and frequency are nearlyequal,only the vibration direction  space quadrature ,it is typical double root.Figure 6: The 8th cavity modal shape5. STRUCTURAL MODAL ANALYSISStructural modes of accumulator include part mode which means sub-structure mode of the detached accumulatorand rigid mode which means whole body mode of the attached accumulator as is discussed before,we identify bothpart and rigid modal parameters by commercial software Test.Lab in the studies below,5.1 Part Modal Analysis By modal impact SIMO approach in Free-Free suspension,we get the first 7 experimental modal frequency as isshown in table 2,from Table 2 we can find that the part modal frequency are much more higher than the band400,500Hz and 1250Hz what we are concerned about due to its high stiffness,basically we can judge its contributionto noise is not high enough,the first two modal shapes are shown in Figure 7,8 for reference.International Compressor Engineering Conference at Purdue, July 14-17, 20081207, Page 4 Table 2: Experimental part modal frequencyModal number 1st 2nd 3rd 4th 5th 6th 7thModal frequency(Hz) 2242 2244 2280 2332 2558 2982 3010Figure 7: The 1st part structural modal shape Figure 8: The 2nd part structural modal shape5.2 Rigid Modal AnalysisAlso by modal impact SIMO approach in Free-Free suspension while attached to main case,we get the first 5 experimental modal frequency as is shown in table 3,from Table 3 we can find that the 3rd and 4th modal frequencyare very closed to the band 400,500Hz and 1250Hz respectively what we are concerned about, obviously these twomodal shapes are all accumulator rigid structural modes as are shown in Figure 9,10 respectively, and the 3rd is vertical mode,the 4th is horizontal mode. Comparing with 2nd, 7th cavity modes simulated before, we found that theirTable 3: Experimental rigid modal frequencyModal number 1st 2nd 3rd 4th 5thModal frequency(Hz) 98 214 429 1326 2005Accum.Accum.Figure 9: The 3rd rigid structural modal shape Figure 10: The 4th rigid structural modal shapemodal shapes are similar and frequency are adjacent respectively, combining the sound source identification resultsdiscussed before basically we can judge its contribution to noise is high possible due to coupling of rigid structuraland cavity modes.6. NOISE EXPERIMENTAL VALIDATION According to the analysis and judgement before, mainly noise contribution of the accumulator on band 400,500Hzand 1250Hz in this case is because of the coupling of rigid structural and cavity modes,in order to validate it byInternational Compressor Engineering Conference at Purdue, July 14-17, 20081207, Page 5 experiment,we modify the cavity modes and structural rigid modes respectively to decouple it by structuralmodification,than comparing the noise spectrum before and after the modification.6.1 Cavity Modal ModificationAccording the former analysis that the 2nd cavity mode is low-order axial mode, so we design a ring thin plate in thelower part of the accumulator as is shown in Figue 11 in order tomodify this order modal frequency and try not to influence therigid structural modes.Simulated modal frequency are shown intable 4 by the same parameters and boundary conditions,it shows that the 2nd mode frequency moved from 427 to 321Hz while the7th and 8th mode frequency change few,also the 2nd mode is stillaxial mode as is shown in Figure 12.Noise spectrum comparisonbefore and after the modification is shown in Figure 13, from it we   Figure 11: Accumulator with plate PlateTable 4: Simulated cavity modal frequency with plateModal number 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10thModal frequency(Hz) 187 321 564 823 940 981 1256 1257 1303 130328.18 17782.7950 63 80 100 160 250 400 630 1000 1600 2500 4000 6300Octave 1/3Hz0.0070.00dB(A)W0.0070.00dB WA L50040069.869.2Curve 500 400 Hz55 56 W38 42 WWithoutWithFigure 12: The 2nd cavity modal shape with plate  Figure 13: Noise spectrum comparisonwith and without platecan find that noise reduction is 14,17dB(A) on band 400,500Hz respectively,few change on band 1250Hz,it matchesthe analysis discussed before,also overall level slightly decrease about 0.6 dB(A).6.2 Rigid Structural Modal ModificationAccording the former analysis that the 3rd and 4th rigid structural modes coupled with the cavity mode,connectionstiffness with the main case need to be changed if we want to move the rigid mode frequency,we modified itsconnection by shorten the suction pipe B,cancelled the holder and welded it directly with the main case as is shownin Figue 14. By the same testing conditions of rigid modes like before,we get the first 5 experimental modalfrequency after welding as is shown in table 5,from the result we can find that the 3rd modal frequency movedsharply from 429 to 920Hz,the 4th modal frequency moved slightly from 1326 to 1412Hz.Noise spectrumcomparison before and after the modification is shown in Figure 15,it shows that noise reduction is 13,14,8dB(A) onband 400,500,1250Hz respectively,that matches the analysis discussed before,also overall level slightly decreaseabout 1.1 dB(A).Table 5: Experimental rigid modal frequency after connection modificationModal number 1st 2nd 3rd 4th 5thModal frequency(Hz) 316 343 920 1412 2125International Compressor Engineering Conference at Purdue, July 14-17, 20081207, Page 6 28.18 17782.7940 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000Octave 1/3Hz-10.0070.00dB(A)W-10.0070.00dB WA L400 500 125068.867.7Curve 400 500 1250 Hz59 52 65 W46 38 57 WWeldingBeforeAfterFigure 14: Accumulator connection   Figure 15: Noise spectrum comparison beforemodification    and after connection modification7. CONCLUSIONSAccumulator has a series of part and rigid structural modes because it is a thin-walled structure attached to maincase,noise peak is possible to happen because of  resonance if cavity modes couple with some structural modes and its frequency are closed to the vibration or noise frequency of  the main case,it is possible to decrease its noisecontribution and eliminate the noise peak by modification of the cavity modes or structural rigid modes to decoupleit.In this paper,noise mechanism and acoustic characteristics of accumulator due to coupling of cavity and structuralmodes is studied systematically combining theory,experiment and simulation,it is proved that the mathematicalmodel,cavity modal simulation and structural modal experiment are effective and reliable approach to analyze theacoustic characteristics of accumulator.REFERENCES[1] Jin-dong Kim,Byung-chan Lee,Jeong-yong Bae,Jong-ok Ban and Young-ho Kim,Noise Reduction of A RotaryCompressor Using Structural Modification of The Accumulator,Proceedings of the 1998 International Compressor Engineering Conference at Purdue,Vol.I,p.355-360[2] Wei Zhou,Han-Jun Kim and Jay Kim,Numerical Prediction of Radiated Noise Level From SuctionAccumulators of Rotary Compressors, Proceedings of the 1998 International Compressor Engineering Conference at Purdue,Vol.I,p.373-378[3] Semyung Wang,Jongchan Park,In soo Hwang and Byoungha Kwon,Sound Reduction of Rotary CompressorUsing Topology Optimization, Proceedings of the 2002 International Compressor Engineering Conference at Purdue,C14-4[4] Dayou Ma,Noise Control Technology,Science Press,1987.7 [5] Wentang Ren,Jian Zhao,Xiaokuan Li,Industrial Noise and Vibration Control Technology,Metallurgy IndustryPress,1989.12[6] Numerical Acoustics,SYSNOISE On Line Help [7] Test.Lab 6A Manuals,LMS International Beijing Office,2006.1International Compressor Engineering Conference at Purdue, July 14-17, 2008

Analysis of Acoustic Characteristics of Accumulator of Rotary Compressor

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2855&amp;context=icec

Analysis of Acoustic Characteristics of Accumulator of Rotary Compressor

Abstract

Similar works

Full text

Available Versions

Purdue E-Pubs