962847_mccluer

962847_mccluer - NASA Technical Memorandum 110423...

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National Aeronautics and Space Administration Megan S McCluer NASA Technical Memorandum 110423 Helicopter Blade-Vortex Interaction Noise with Comparisons to CFD Calculations December 1996
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National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035-1000 NASA Technical Memorandum 110423 December 1996 Helicopter Blade-Vortex Interaction Noise with Comparisons to CFD Calculations Megan S McCluer, Ames Research Center, Moffett Field, California
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iii Contents Page List of Tables . ........................................................................................................................................................... iv List of Figures. .......................................................................................................................................................... iv Nomenclature. ........................................................................................................................................................... vii Summary. .................................................................................................................................................................. 1 1 Introduction . ................................................................................................................................................... 1 1.1 Rotorcraft Aeroacoustics. .................................................................................................................... 1 1.2 Previous Work in BVI Acoustics . ....................................................................................................... 4 1.3 Motivation and Objectives . ................................................................................................................. 6 1.4 Organization . ....................................................................................................................................... 7 2 The Experiment. ............................................................................................................................................. 8 2.1 Experimental Set-up . ........................................................................................................................... 8 2.2 Acoustic Data Acquisition and Analysis . ........................................................................................... 10 3 Computational Issues . .................................................................................................................................... 14 3.1 Governing Equations. .......................................................................................................................... 14 3.2 Computational Grid. ............................................................................................................................ 14 3.3 Vortex Management . ........................................................................................................................... 15 3.4 Vortex Model . ..................................................................................................................................... 15 3.5 Time Accuracy . ................................................................................................................................... 16 3.6 Previous Validations . .......................................................................................................................... 16 4 Results and Discussion . ................................................................................................................................. 17 4.1 Experimental Data. .............................................................................................................................. 17 4.2 Comparison of CFD and Experiment. ................................................................................................. 20 4.3 Thickness Effects . ............................................................................................................................... 22 4.4 Effect of Vortex Parameters on CFD Results . .................................................................................... 23 4.5 Effect of Newton Sub-Iterations . ........................................................................................................ 25 4.6 Study of Directionality . ....................................................................................................................... 27 4.7 Summary of Results . ........................................................................................................................... 29 5 Summary and Conclusions . ........................................................................................................................... 30 5.1 Summary . ............................................................................................................................................ 30 5.2 Conclusions . ........................................................................................................................................ 30 Appendix A – Computational Fluid Dynamics Model. ............................................................................................ 31 Appendix B – Comparison of Experimental and Computational Results . ............................................................... 37 References. ................................................................................................................................................................ 47
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iv List of Tables Page 4.1 Peak-to-peak pressure amplitude in Pascals for experimental data . ............................................ 19 4.2 Expected arrival time (as computed by linear theory) in blade azimuth angle for peak pressure amplitudes to reach each microphone location . .................................................... 19 4.3 Peak-to-peak amplitudes for CFD calculations with a nondimensional vortex strength of 0.406 and difference from experimental results . ......................................................................... 21 4.4 Peak-to-peak pressure amplitude comparisons . ........................................................................... 26 List of Figures 1.1 Examples of aerodynamic interactions of a helicopter that are possible noise sources. .............. 2 1.2 The frequency spectrum of a typical helicopter far-field noise signal. ........................................ 2 1.3 Schematic comparing general amplitude and wave shapes for thickness effects and HSI noise . .................................................................................................................. 3 1.4 Flightpath effects on BVI noise . .................................................................................................. 3 1.5 Schematic of parallel BVI on a helicopter. .................................................................................. 4 1.6 Example of the source of BVI noise . ........................................................................................... 4 2.1 Schematic of experimental set-up in wind-tunnel test section. .................................................... 8 2.2 Photograph of BVI experiment in the ARC 80- by 120-Foot Subsonic Wind Tunnel . ............... 8 2.3 Position of microphones 6 and 7 with respect to rotor blade at 0.88R and 180 deg azimuth angle . ................................................................................................................ 9 2.4 Schematic of rotor quarter-chord line passing over microphones . .............................................. 9 2.5 Schematic of test set-up (as viewed from above) showing parallel BVI occurring at the rotor quarter-chord . ............................................................................................................ 10 2.6 Schematic illustrating four BVI geometries examined at two different hover tip Mach numbers. ............................................................................................................................. 10 2.7 Example of unaveraged experimental data in original units. Case I, M tip = 0.6, microphone 6. ............................................................................................................................... 11 2.8 Frequency spectrum of 30 revolutions of experimental data. Case I, M tip = 0.6, microphone 6. ............................................................................................................................... 11 2.9 Example of a single revolution of pressure data, unaveraged in original units.
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