The Dynamics of Static Stall

The dynamic process of flow separation on a stationary airfoil in a uniform flow was investigated experimentally by means of time-resolved measurements of the velocity field and the airfoil's surface pressure distribution. The unsteady movement of the separation point, the growth of the separated region, and surface pressure fluctuations were examined in order to obtain information about the chronology of stall development. The early inception of stall is characterised with the abrupt upstream motion of the separation point. During subsequent stall development, large scale shear layer structures are formed and grow while travelling downstream. This leads to a gradual increase of the separated flow region reaching his maximum size at the end of stall development which is marked by a significant lift drop.