A Semi-empirical Approach to Simulate the Effects of Higher Harmonic Rotor Blade Control Using Prescribed Wake

Abstract

To account for the effect of higher harmonic rotor blade control (HHC) on the wake geometry and hence on blade-vortex interaction (BVI) locations free-wake methods are regularly used within comprehensive rotor simulation environments. Prescribed wake formulations are much faster than free-wake codes, but require á priori information of the induced velocity field within the rotor disk to account for wake perturbations. In this paper a semi-empirical approach to account for the effects of HHC on the prescribed wake geometry is described and validated against data from the 2nd HHC Aeroacoustic Rotor Test (HART II). This covers the computation of the global induced velocity perturbations due to HHC from the blade loading time histories, the computation of the wake geometry perturbations due to these (both is performed within DLR’s high resolution comprehensive rotor code S4), and finally the noise radiation using DLR’s acoustic code APSIM. The results have first been presented at the American Helicopter Society 65th Annual Forum, Grapevine, Texas, May 27-29, 2009.