Dynamic Stall Vortex Development and the Surface Pressure Field of a Pitching Airfoil.

摘要

A detailed examination of simultaneous digitally enhanced flow visualization results and surface pressure measurements was conducted to develop insight into the relationships between dynamic stall vortex development and airfoil surface pressure levels. The experimental situation involved a two-dimensional NACA 0015 airfoil driven at constant pitching rates over attack angles from zero to 60 degrees. Specific attention was focussed on moderately low non-dimensional pitch rates such that only a single dynamic vortex was present on the airfoil surface at any one time. The analyses show that the development of a dynamic stall vortex over the top surface of the airfoil does not enhance the instantaneous lift.l The initiation of the dynamic stall vortex appears to correspond closely to a leveling of the lift curve as a function of attack angle. Later rapid growth of the stall vortex accompanies a decrease in lift. The eventual detachment of the stall vortex from the airfoil corresponds to a simultaneous decrease in the pressure drag on the airfoil. (JD)