This paper describes a methodology to quantitatively determine the contributions of individual advancing and retreating side blade-vortex interactions to the total radiated BVI noise. It can be used to identify which interactions are most acoustically significant, and potentially improve the effectiveness of BVI alleviation strategies by ensuring that secondary interactions do not gain in strength even while the dominant ones are being weakened. The methodology is based on first identifying the tip-vortex generating a particular interaction and then calculating the blade loading, acoustic pressure signal, and BVI sound pressure levels due to this single tip-vortex. This yields detailed quantitative information on the intensity and directionality of the noise due to specific interactions (associated with specific tip-vortices), as well as the contribution of the individual interactions to the total radiated BVI acoustic field. It is further demonstrated that the impulsive loads, acoustic pressure, and BVI noise can be predicted, without loss of accuracy, by considering only those portions of the tip-vortices generating close, near-parallel interactions in the 1st and 4th quadrants (instead of the entire tip-vortices extending over several rotor revolutions). The use of the current noise decomposition methodology in an application is demonstrated, and it is shown that when the descent rate is changed, or an X-force is introduced, the dominant blade-vortex interactions change.
A method to evaluate the contributions of individual interactions to helicopter blade-vortex interaction noise
Ermittlung des von einem Rotorblatt beim Durchqueren der Wirbelschleppe gelieferten Beitrags zum Schallfeld eines Hubschraubers
Journal of the American Helicopter Society ; 48 , 4 ; 287-299
2003
13 Seiten, 16 Bilder, 16 Quellen
Article (Journal)
English
Influence of Individual Interactions on Helicopter Blade-Vortex Interaction Noise
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