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.