Dynamic recovery to fully attached aerofoil flow from deep stall

We present results from a comprehensive analysis of pressure data from several two-dimensional aerofoil models performing constant pitch rate ramp-down motions from the fully separated state to the fully attached state. The salient observation is that, a short while after reattachment is first observed at the leading edge, a weak disturbance travels from the leading edge to the trailing edge, and this disturbance causes a characteristic wave on the pressure data. The speed of the wave is uniform along the chord and is predominantly independent of aerofoil profile and reduced pitch rate. This contrasts with the rate of attachment, which is strongly pitch rate dependent. It is suggested that the wave indicates convection of wake fluid over the aerofoil surface.