Dynamic stall alleviation using leading edge deformation

Dynamic stall on a two dimensional oscillating airfoil is alleviated through the use of a dynamically deforming leading edge. The airfoil undergoes three motions: pitching, plunging, and simultaneous pitching and plunging. Numerical investigation of dynamic stall prevention using a thin layer, Navier-Stokes flow solver is presented. Dynamic stall prevention, postponement, and alleviation is shown for high angles of attack, primarily 20° effective angle of attack. An investigation of the combined aerodynamic interactions of the local components of the flow field is presented for understanding and alleviating dynamic stall.; The effects of the deflection schedule are explained by examining the flowfield about the airfoil as it undergoes each particular motion. Dynamic stall resulting from pitching motions is fundamentally different from dynamic stall resulting from plunging motion, and therefore the ability of leading edge deformation to prevent dynamic stall becomes dependent on airfoil motion. Performance results for steady airfoils with a constant deformation angle, pitching or plunging airfoils with a constant deformation angle, and steady airfoils with a deforming leading edge are given to explain why a leading edge deformation scheme either fails or succeeds with dynamic stall alleviation.; Two control systems are developed to alleviate dynamic stall. The first method is a heuristic prescribed deformation schedule based on results from a sample of different deformation schedules. The second method is a controlled deformation schedule based on the resulting flow field about the surface of the airfoil while oscillating. The second control system is developed to keep the peak suction coefficient of pressure value below a specified limit. The increase in peak coefficient of pressure values creates a more favorable pressure gradient at the leading edge, which reduces the tendency for the flow to separate. This control system is based on understanding the individual effects of leading edge deformation angle and leading edge deformation pitch rate on the value of the peak coefficient of pressure.; The prescribed deformation schedule and the developed controlled deformation schedule is tested for each of the three airfoil motions. Results from the deflection schedules are compared at Mach numbers, Reynolds numbers, and reduced frequencies typical of rotorcraft environments.