UNSTEADY SEPARATION FROM THE LEADING-EDGE OF A THIN AIRFOIL

At high Reynolds numbers, the process leading to dynamic stall on airf oils initiates in the leading-edge region. For thin airfoils, the loca l motion near rounded leading edges can be represented as flow past a parabola and when the mainstream flow is at an angle of attack to the airfoil, a portion of the boundary layer will be exposed to an adverse pressure gradient. Once the angle of attack exceeds a certain critica l value, it is demonstrated that unsteady boundary-layer separation wi ll occur in the leading-edge region in the form of an abrupt focused b oundary-layer eruption. This process is believed to initiate the forma tion of the dynamic stall vortex. For impulsively-started incompressib le flow past a parabola, a generic behavior is found to occur over a r ange of angles of attack, and a limit solution corresponding to relati vely large angles is found. The separation in the leading-edge region develops in a zone of relatively limited streamwise extent over a wide range of angles of attack. This suggests that localized control measu res (such as suction) may possibly be effective at inhibiting separati on. (C) 1996 American Institute of Physics.