Prediction of Rotor High-Speed Impulsive Noise with a Combined Cfd-Kirchoff Method

ISSN： 0022-460X

Source： Journal of Sound and Vibration, Vol.207, Iss.4, 1997-11, pp. : 453-464

Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.

Previous Menu Next

Abstract

A combined Computational Fluid Dynamics (CFD)-Kirchoff method is presented for predicting high-speed impulsive noise generated by a rotor in hover. Two types of Kirchoff integral formulas are used: one of them is a classical linear Kirchoff formulation and the other a non-linear Kirchoff formulation. An Euler finite-difference solver is executed first, from which a flow field is obtained to be used as an input to the Kirchoff formulation to predict the acoustic far-field. The calculations are performed at Mach numbers of 0·90 and 0·95 to investigate the effectiveness of the linear and non-linear Kirchoff formulas for delocalized flow. During these calculations, the retarded time equation is also carefully examined, in particular, for the cases where a control surface is located outside the sonic cylinder, for which multiple roots are obtained. Predicted results of acoustic far-field with the linear Kirchoff formulation agree well with the experimental data when the control surface is at a particular location (Rcs/R=1·46), but the correlation weakens as it moves away from this specific location of the control surface due to the delocalized non-linear aerodynamic flow field. Calculations based on the non-linear Kirchoff equation using the sonic cylinders as the control surfaces show reasonable agreements with the experimental data in the negative amplitudes for both tip Mach numbers of 0·90 and 0·95, except for some computational integration problems over a shock. It can be concluded that a non-linear formulation is necessary if the control surface is close to the blade and the flow is delocalized.Copyright 1997 Academic Press Limited