Controlled Aerodynamic Loads on an Airfoil in Coupled Pitch/Plunge by Transitory Regulation of Trapped Vorticity

The aerodynamic loads on an airfoil moving in coupled, time-periodic pitch-plunge beyond the static stall margin are controlled using transitory regulation of trapped vorticity concentrations. ~Actuation is effected by a spanwise array of integrated miniature chemical (combustion based) impulse actuators that are triggered intermittently during the airfoil's motion and have a characteristic time scale that is an order of magnitude shorter than the airfoil's convective time scale. ~Each actuation pulse effects momentary interruption and suspension of the vorticity flux with sufficient control authority to alter the airfoil's global aerodynamic characteristics throughout its motion cycle. ~The effects of the actuation are assessed using time-dependent measurements of the lift and pitching moment coupled with time-resolved particle image velocimetry over the airfoil and in its near wake that is acquired phased-locked to its motion. ~It is shown that while the presence of the pitch-coupled plunge delays lift and moment stall during upstroke, it also delays flow reattachment during the downstroke and results in significant degradation of the pitch stability. ~These aerodynamic shortcomings are mitigated using superposition of a limited number of pulses that are staged during the pitch/plunge cycle and lead to enhancement of cycle lift and pitch stability, and reduces the cycle hysteresis and peak pitching moment.