A Permeable Self-adaptive Integration Surface for HSI Noise Prediction of Helicopter Rotor in Forward Flight

In this paper, a new permeable self-adaptive integration surface is developed for the prediction of rotor HSI noise by KFWH method in forward flight. Firstly, the nonlinear near flowfield solution is computed by a N-S solver and as input for acoustic calculations by KFWH formula. Then, the acoustic pressure predictions of the AH-1 model rotor with cylinder-shaped integration surfaces at different locations are shown, which reveals that the results calculated by KFWH method show a large sensitivity to the location of integration surface. In order to avoid the calculation error caused by the uncertainties in determining the cylinder-shaped integration surface, a new permeable self-adaptive integration surface is determined by density adaptively according to some principles. These principles have been validated in hover flight in previous paper. Then, the acoustic pressure of AH-1 model rotor at different tip Mach numbers and different observer locations are simulated. In comparison with cylinder-shaped integration surface, the self-adaptive integration surface, which is determined by density, can reach higher accuracy in the prediction of rotor HSI noise.