Research on Helicopter Rotor Acoustic Noise Prediction Method Based on Convected FW-H Equation

The acoustic stealth design of helicopters have increasingly been a research hotpot with the development of the helicopter technology. Aiming at the prediction of the acoustic noise of the helicopter's rotor, which can be the main source of the noise, a method based on Computational Fluid Dynamics (CFD) technology is established. In this paper, the surface pressure distribution of the blades is solved by CFD method while the acoustic noise can be obtained by convected FW-H equation that takes consideration of inflow for more accurate solutions. The efficiency and validity is verified in this study by several examples about isom thickness noise prediction, dipole noise prediction and acoustic noise calculation, which show the predicted solution fits the analytic solution quite well. Significant factors including inflow, collective pitch, rotating speed and airfoil are analyzed and discussed in detail. It can be obtained from the results that the factors above decisively raise the acoustic noise. The affection on thickness noise is caused by all the factors except the collective pitch, while the loading noise is impacted by all these factors. Choosing appropriate design parameters is essential for improving the acoustic stealth characteristics of the helicopter and therefore the presented method based on convected FW-H equation can be effective and helpful for this.