Effect of Tip Vortex Dissipation on the Prediction of Helicopter BVI Noise

Abstract

Blade Vortex Interaction (BVI) noise of helicopter is predicted by using CFD analysis based on three dimensional Euler equations and subsequent acoustic analysis. In the CFD analysis, Beddose generalized wake model is used to prescribe the geometrical position of tip vortices in the wake, and Lamb-Oseen model is used to consider the vortex dissipation in order to avoid overestimation of BVI noise which sometimes occurs when the dissipation is not considered in the model. Lamb-Oseen model simulates the vortex dissipation by enlarging the core radius and attenuating the swirl velocity of vortex. The calculated sound pressure shows adequate decrease of BVI noise peaks as well as the reduction of small fluctuations compared to the no dissipation result. In consequence, the use of vortex dissipation model like Lamb-Oseen model is effective to improve the quality of calculation by avoiding the overestimation of BVI noise and by reducing the unrealistic fluctuations in the sound pressure calculation.