Vibration Reduction in Rotorcraft Using Closed-Loop Active Flow Control

The vibration reduction obtained using active flow control (AFC) implemented on helicopter rotor blades is examined using comprehensive aeroelastic simulations. The flow control device consists of two fluidic jet actuators installed near the trailing edge of the blades on both the pressure side and the suction side. Closed-loop control simulations based on the higher-harmonic control (HHC) algorithm are developed to account for the discrete operating characteristics of the AFC actuators, since each actuator is either on or off at a fixed jet strength. The sensitivity of the closed-loop vibration reduction to the actuation power available, enforced as a saturation limit in the HHC algorithm, is examined. Results demonstrate the effectiveness and control authority of AFC for vibration reduction: up to 83% reduction of the 4/rev vibratory hub loads is possible. The vibration reduction is comparable to that obtained using a mechanically operated microflap operating in a closed-loop mode. Finally, the effect of AFC on the overall rotor performance during closed-loop vibration control is determined. Results indicate that moderate levels of vibration reduction are possible, with minimal impact on the overall performance when low actuation power is used. When the actuation power is increased, a diminishing level of improvement in the vibration reduction is observed, and the cost to overall performance increases significantly.