Onset of Leading Edge Separation Effects under Dynamic Conditions and Low Mach Number

A new criterion for the onset of airfoil separation under dynamic conditions has been derived and practical means of application developed. On the basis that prior to dynamic stall the flow can be calculated using potential models, the chordwise loading distribution is examined for the dynamic case. It is shown that the important components of the instantaneous distribution can be expressed in terms of the additional loading due to angle of attack derived from the static case, scaled and modified by time dependent circulatory and rate terms. This form of solution enables use to be made of chordwise velocity distributions obtained from more exact methods, the results of which can be linearised for application to the dynamic case. A correlation of leading edge stall by the reseparation process, performed by NASA in 1959 has been found to provide a criterion for the maximum leading edge velocities that can be sustained and is used to indicate initiation of the separation process, i.e. leading edge vortex shedding.