Numerical simulations of active flow control for rotor vibration reduction at moderate to high advance ratios

Abstract

The vibration reduction capability of active flow control (AFC) jets installed on the blades of a helicopter rotor is examined using comprehensive aeroelastic simulations. The simulations represent a four-blade hingeless rotor operating at several different advance ratios in the range of 0.20??????0.35. The closed-loop control scheme for reducing vibrations is based on the higher-harmonic control (HHC) algorithm, subject to actuator saturation constraints. Dynamic stall strongly influences vibrations at ????=0.35. Furthermore, the control sen-sitivity matrix used in the HHC algorithm varies significantly depending on the advance ratio. This produces different weightings of the 2-, 3-, 4-, and 5/Rev control harmonics used for vibration reduction. The overall level of vibrations at the rotor hub is consistently reduced by 70% to 80% below the baseline for all advance ratios considered. The reduction of in-plane shear force vibrations improves as the advance ratio increases, indicat-ing that the adverse effects of dynamic stall are alleviated by AFC. The performance penalty associated with vibration reduction is also calculated. The additional rotor power required increases with advance ratio, due to increased drag penalty associated with fluidic actuation.