Acoustic source and data acquisition system for a helicopter rotor blade-vortex interaction (BVI) noise reduction experiment PDF
Preview Acoustic source and data acquisition system for a helicopter rotor blade-vortex interaction (BVI) noise reduction experiment
NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS ACOUSTIC SOURCE AND DATA ACQUISITION SYSTEM FOR A HELICOPTER ROTOR BLADE- VORTEX INTERACTION(BVI) NOISE REDUCTION EXPERIMENT. by Brian D. Roth December, 1996 Thesis Advisors: Robert M. Keolian Steven R.Baker Thesis R77927 Approved for public release; distribution is unlimited. REPORT DOCUMENTATION PAGE FormApprovedOMBNo.0704-0188 Publicreportingburdenforthiscollectionofinformationisestimatedtoaverage I hourperresponse,includingthetimeforreviewinginstruction,searchingexistingdata sources,gatheringandmaintainingthedataneeded,andcompletingandreviewingthecollectionofinformation.Sendcommentsregardingthisburdenestimateoranyother aspectofthiscollectionofinformation,includingsuggestionsforreducingthisburden,toWashingtonHeadquartersServices,DirectorateforInformationOperationsand Reports, 1215JeffersonDavisHighway,Suite1204,Arlington,VA22202-4302,andtotheOfficeofManagementandBudget,PaperworkReductionProject(0704-0188) WashingtonDC20503. 1. AGENCYUSEONLY(Leaveblank) 2. REPORTDATE REPORTTYPEANDDATES COVERED December 1996 Master's Thesis 4. TITLEANDSUBTITLEACOUSTIC SOURCE AND DATA FUNDING NUMBERS ACQUISITION SYSTEM FOR A HELICOPTER ROTOR BLADE-VORTEX INTERACTION^VI) NOISE REDUCTION EXPERIMENT. 6. AUTHOR(S)Brian D. Roth 7. PERFORMINGORGANIZATIONNAME(S) ANDADDRESS(ES) PERFORMING Naval Postgraduate School ORGANIZATION Monterey CA 93943-5000 REPORTNUMBER SPONSORING/MONITORING AGENCYNAME(S) ANDADDRESS(ES) 10. SPONSORING/MONITORING AGENCYREPORTNUMBER 11. SUPPLEMENTARYNOTES The views expressed in this thesis arethose ofthe authorand do not reflectthe official policy orposition ofthe Department ofDefense orthe U.S. Government. 12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTIONCODE Approved forpublic release; distribution is unlimited. 13. ABSTRACT(maximum200words) One ofthe most objectional noises produced by a helicopter is due to interaction ofa rotor blade with a previously shed vortex. Various methods have been proposed to reduce this blade-vortex interaction (BVI) noise; this investigation is concerned with BVI noise reduction by rotor blade tip design modifications. Potentially much can be learned regarding the prospect for success ofa candidate rotor blade design at greatly reduced time and money by performing acoustic scattering measurements in an anechoic chamber. It is proposed that a rotor blade which scatters acoustic waves less could be expected to produce less BVI noise. This thesis describes the development ofthe acoustic source and computer controlled data acquisition system for such a scattering experiment. 14. SUBJECTTERMS Blade-Vortex Interaction (BVI), Acoustic scattering measurements, 15. NUMBEROF PAGES 75 Anechoic chamber, Helicopternoise reduction 16. PRICECODE 17. SECURrTYCLASSIFICA- 18. SECURITYCLASSIFI- 19. SECURITYCLASSIFICA- 20. LIMITATIONOF TIONOFREPORT CATIONOFTHIS PAGE TIONOFABSTRACT ABSTRACT UL Unclassified Unclassified Unclassified NSN7540-01-280-5500 StandardForm 298 (Rev. 2-89) PrescribedbyANSIStd.239-18298-102 11 Approved for public release; distribution is unlimited. ACOUSTIC SOURCE AND DATA ACQUISITION SYSTEM FOR A HELICOPTER ROTOR BLADE-VORTEX INTERACTION(BVI) NOISE REDUCTION EXPERIMENT. Brian D. Roth Lieutenant, United States Navy B.S., Taylor University, 1988 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN ENGINEERING ACOUSTICS from the NAVAL POSTGRADUATE SCHOOL December 1996 ABSTRACT Oneofthe most objectional noises produced by a helicopter is due to interaction ofa rotorblade with a previously shed vortex. Various methods have been proposed to reduce this blade-vortex interaction (BVI) noise; this investigation is concerned with BVI noise reduction byrotorblade tip design modifications. Potentially much can be learned regarding the prospect for success ofacandidate rotor blade design at greatly reduced time and money byperforming acoustic scattering measurements in an anechoic chamber. It is proposed that arotorblade which scatters acoustic waves less couldbe expected to produce less BVI noise. This thesis describes the development ofthe acoustic source and computer controlled data acquisition system for such a scattering experiment. VI TABLE OF CONTENTS INTRODUCTION I. 1 A. BACKGROUND AND MOTIVATION 1 B. SOURCES OF HELICOPTERNOISE 2 C. SOLUTIONS TO THE HELICOPTER NOISE PROBLEM 6 D. SCOPE 7 II. THEORY OF BLADE-VORTEX INTERACTION NOISE (BVI) NOISE 9 III. ACOUSTIC SOURCE AND DATA ACQUISITION SYSTEM 23 A. DESCRIPTION OF ACOUSTIC SCATTERING EXPERIMENT 23 B. ACOUSTIC SOURCE 24 C. DATA ACQUISITION SYSTEM 27 1. SOURCE SIGNAL PROCESSING 28 2. SOURCE EXPERIMENT DESCRIPTION AND RESULTS 30 IV. CONCLUSIONS AND RECOMMENDATIONS 39 SUMMARY A. 39 B. RECOMMENDATIONS FOR FOLLOW-ON RESEARCH 39 APPENDIX A. DATA ACQUISITION BOARD 41 APPENDIX B. ITHACO LOW NOISE PRE-AMP SPECIFICATIONS 47 APPENDIX C. PIONEER SPEAKER SPECIFICATIONS 49 APPENDIX D. ANECHOIC CHAMBER 51 APPENDIX E. LABVIEW COMPUTER CODE 53 LIST OF REFERENCES 59 INITIAL DISTRIBUTION LIST 61 vn Vlll
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