Unsteady separation from the leading edge of a thin airfoil

At high Reynolds numbers, the process leading to dynamic stall on airfoils initiates in the leading‐edge region. For thin airfoils, the local 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 critical value, it is demonstrated that unsteady boundary‐layer separation will occur in the leading‐edge region in the form of an abrupt focused boundary‐layer eruption. This process is believed to initiate the formation of the dynamic stall vortex. For impulsively‐started incompressible flow past a parabola, a generic behavior is found to occur over a range of angles of attack, and a limit solution corresponding to relatively 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 suggest...

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