Experiments on the unsteady massive separation over an aerofoil

Instantaneous flow fields over a NACA 0012 aerofoil at the stall and post-stall angles of attack have been measured using the time-resolved particle image velocimetry technique. The time sequence of the measured data reveals that the massive separation over the upper surface of the aerofoil is intermittent in nature. This intermittent massive separation is due to the interchange of instability, that is, from a convective to an absolute instability and from an absolute to a convective instability. A physical mechanism for this intermittent massive separation has also been proposed.