Theoretical Investigation of Processes to Dynamic Stall and Control

The present work was mainly concerned with the fundamental processes that occur on a two-dimensional airfoil undergoing a maneuver which normally produces dynamic stall. The results show that, in a high Reynolds number flow, a separation process initiates in the leading-edge region once a certain critical angle of attack is exceeded for a thin airfoil. Much of the work has concentrated on the leading edge region, since a general analysis incorporating the effects of the airfoil wake has shown that for a thin airfoil at angle of attack, the most important separation effects occur in the leading edge region. A number of possible control processes have been considered on a computational basis of the leading-edge region, including selective localized suction and a small moveable portion of the wall. These indicate that the onset of separation can be inhibited at angles of attack beyond the critical value leading to significant increases in lift. Extensive computations have also been carried out for unsteady three dimensional boundary layers induced by vortex motion. The results show that complex separation events occur that involve complication topologies and multiple critical points. A Lagrangian method has been developed which computers the solution at high Reynolds number up to the evaluation of a separation singularity.