The Influence Of A Wind Tunnel On Helicopter Rotational Noise Formulation Of Analysis
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Author | : National Aeronautics and Space Administration (NASA) |
Publisher | : Createspace Independent Publishing Platform |
Total Pages | : 32 |
Release | : 2018-08-16 |
Genre | : |
ISBN | : 9781725624351 |
An analytical model is discussed that can be used to examine the effects of wind tunnel walls on helicopter rotational noise. A complete physical model of an acoustic source in a wind tunnel is described and a simplified version is then developed. This simplified model retains the important physical processes involved, yet it is more amenable to analysis. The simplified physical model is then modeled as a mathematical problem. An inhomogeneous partial differential equation with mixed boundary conditions is set up and then transformed into an integral equation. Details of generating a suitable Green's function and integral equation are included and the equation is discussed and also given for a two-dimensional case. Mosher, M. Ames Research Center NASA-TM-85982, A-9815, NAS 1.15:85982 RTOP 505-42-11...
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Total Pages | : 34 |
Release | : 1984 |
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Total Pages | : 704 |
Release | : 1995 |
Genre | : Aeronautics |
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Author | : United States. Superintendent of Documents |
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Total Pages | : |
Release | : 1985 |
Genre | : Government publications |
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February issue includes Appendix entitled Directory of United States Government periodicals and subscription publications; September issue includes List of depository libraries; June and December issues include semiannual index
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Total Pages | : 654 |
Release | : 1992 |
Genre | : Aeronautics |
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Total Pages | : 1426 |
Release | : 1985 |
Genre | : Government publications |
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Total Pages | : 1386 |
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Genre | : Government publications |
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Author | : United States. Superintendent of Documents |
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Total Pages | : 1466 |
Release | : 1976 |
Genre | : United States |
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Author | : National Aeronautics and Space Administration (NASA) |
Publisher | : Createspace Independent Publishing Platform |
Total Pages | : 60 |
Release | : 2018-07-10 |
Genre | : |
ISBN | : 9781722736873 |
Blade-Vortex-Interaction (BVI) produces annoying high-intensity impulsive noise. NASA Ames collected several sets of BVI noise data during in-flight and wind tunnel tests. The goal of this work is to extract the essential features of the BVI signals from the in-flight data and examine the feasibility of extracting those features from BVI noise recorded inside a large wind tunnel. BVI noise generating mechanisms and BVI radiation patterns an are considered and a simple mathematical-physical model is presented. It allows the construction of simple synthetic BVI events that are comparable to free flight data. The boundary effects of the wind tunnel floor and ceiling are identified and more complex synthetic BVI events are constructed to account for features observed in the wind tunnel data. It is demonstrated that improved recording of BVI events can be attained by changing the geometry of the rotor hub, floor, ceiling and microphone. The Euclidean distance measure is used to align BVI events from each blade and improved BVI signals are obtained by time-domain averaging the aligned data. The differences between BVI events for individual blades are then apparent. Removal of wind tunnel background noise by optimal Wiener-filtering is shown to be effective provided representative noise-only data have been recorded. Elimination of wind tunnel reflections by cepstral and optimal filtering deconvolution is examined. It is seen that the cepstral method is not applicable but that a pragmatic optimal filtering approach gives encouraging results. Recommendations for further work include: altering measurement geometry, real-time data observation and evaluation, examining reflection signals (particularly those from the ceiling) and performing further analysis of expected BVI signals for flight conditions of interest so that microphone placement can be optimized for each condition. Rogers, James C. and Dai, Renshou Ames Research Center...
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Total Pages | : 538 |
Release | : 1991 |
Genre | : Aeronautics |
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