Predictions of Transonic Rotor Noise by KFWH Method with A Permeable Self-Adaptive Integration Surface

In this paper, a new permeable self-adaptive integration surface is developed for the evaluation of transonic rotor noise by KFWH method. 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 UH-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 uncertainties in determining the cylinder-shaped integration surface, a new permeable self-adaptive integration surface is determined by pressure gradient or density adaptively according to some principles. Then, the acoustic pressure of UH-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, whether it is determined by pressure gradient or by density, can both reach higher accuracy in the prediction of transonic rotor noise. Moreover, the numerical results with self-adaptive integration surfaces given by density perturbation value confirm to the experimental data better.