A Theoretical Investigation of Unsteady Separation Phenomena Related to Dynamic Stall

The objective of this research was to identify the principal cause and effect relationships in dynamic stall at large Reynolds numbers, as well as possible means for controlling the process. At high Reynolds numbers, it is demonstrated the formation of the dynamic stall vortex initiates for all airfoil shapes via an unsteady separation of the boundary layer near the leading edge. The stall vortex ultimately detaches from the upper surface by provoking an unsteady separation of the surface layer near midchord. At least two methods of controlling separation at various stages in the cycle have been identified, namely (1) suction near the leading nose or at midchord and (2) a moving portion of the surface. The present work shows how separation can be suppressed and makes significant contributions to the theory of unsteady boundary-layer separation. A general analysis of unsteady two-dimensional airfoil maneuvers was initiated and is currently under study as a possible third means of control.