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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