Nonlinear propagation distortion causes energy to be shifted to the high-frequency end of the spectrum. As a result, traditional linear calculations, which include geometrical spreading and atmospheric absorption, underestimate the noise levels at high frequencies. The effect has been investigated for aircraftjet noise, but less attention has been given to helicopters. The Burgers equation, which incorporates nonlinear propagation distortion effects, is employed for the prediction of the noise spectrum away from the helicopter. It is shown that nonlinear effects can be sizable for blade-vortex interaction noise produced by helicopter's main rotor. However, employment of the Burgers equation can be time consuming to be included in routine calculations. It also requires knowledge of the initial pressure time signal. The power spectrum alone, which is usually known, is not sufficient. In the present work, three prediction methods are presented that are based on the Burgers equation and address the above-mentioned concerns.
Prediction of nonlinear propagation distortion in blade-vortex interaction noise
Vorhersage der nichtlinearen Ausbreitungsstörung bei der Lärmentstehung infolge Blatt/Wirbel-Wechselwirkung
Journal of the American Helicopter Society ; 55 , 3 ; 032002/1-032002/11
2010
11 Seiten, 14 Bilder, 1 Tabelle, 24 Quellen
Article (Journal)
English
Prediction of Nonlinear Propagation Distortion in Blade-Vortex Interaction Noise 032002
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