Prediction of aeroacoustic noise for helicopter rotors based on vorticity confinement method

In the numerical simulation of helicopter rotor in hover flight, the prediction of aeroacoustic noise for helicopter rotors is highly dependent on the capturing accuracy of vortical flow structure. In this paper, the compressible Euler equations are solved by using a finite volume method with a central scheme to simulate the flow around helicopter rotors, and the Ffowcs Williams-Hawkings (FW-H) equations are utilized to predict the aeroacoustic noise. In order to reduce the numerical dissipation and preserve the vortical flow structure on the wing tip or rotor blade tip, a vorticity confinement method is introduced to the original Euler solver. The method is more applied to the flow around ONERA M6 wing, UH-1H, Caradonna and AH-1/OLS helicopter rotors. It is shown that the method is more able to preserve the vortical flow structure on coarse grids and the predicted results of aeroacoustic noise for helicopter rotors are all improved. The results show that the predict accuracy is also improved, even for non-lifting flight. The effect of vorticity confinement coefficient on the stability and numerical results is investigated. Finally, the effect of conditions (such as grid size, blade tip Mach number, pitch angle, and aspect ratio) on critical vorticity confinement coefficient is concluded.