| At high Reynolds numbers, the process leading to dynamic stall of thin airfoil is known to initiate in the leading nose region. Once airfoil is set in motion in a uniform stream, a thin boundary layer develops in order to reduce the flow to relative rest on the surface. The boundary layer leaves the trailing edge of the airfoil, shedding vorticity into a thin wake that lengthens with time and can support a jump in tangential velocity. In this study, the viscous response is studied in the leading nose region as the airfoil performs a pitch up maneuver in a uniform stream.; The unsteady inviscid motion is constructed for an airfoil undergoing a maneuver on the basis of thin airfoil theory, wherein the airfoil is thin and the flow perturbations at any stage are small (with respect to the uniform flow).; Two-dimensional thin symmetrical airfoil with a cusped trailing edge is considered with finite developing wake attached to the trailing edge. Solutions for the velocity field, circulation density in the wake and lift on the airfoil are obtained for a specified maneuver. Then matched asymptotic expansions are used to obtain the inviscid flow in the vicinity of the leading edge region, which is approximated by a parabola. The equation for the time-dependent location of the front stagnation point is derived. Lastly, the boundary-layer development at the leading edge of the airfoil is considered in the case where the airfoil undergoes high-frequency, small amplitude oscillations in the angle of attack about a constant angle of attack. The effect of the imposed frequency and amplitude of oscillation on the boundary-layer development is investigated numerically. It is shown that under certain conditions boundary-layer separation can be substantially retarded. This suggests a possible strategy for controlling the onset of dynamic stall. |
