"Vortical Flow Control Using a Moveable Stagnation Point"
L.A. Darden and N.M. Komerath

American Physical Society, November, 1994

Abstract
Asymmetric vortex patterns form over aircraft forebodies at high incidence. This paper studies the response of such vortices to rapid motion of the nose stagnation point. Laser sheet videography is used to capture the motion history of the vortex patterns, with the model placed in a low-speed wind tunnel. The motion of the stagnation point was recorded using a simple shadow technique. Asymmetric vortices were observed at all incidence angles greater than 30 deg. Two time series, one representing the stagnation point motion and the other the position at which the zero-vorticity contour (ZVC) of the vortex system intersected the model surface, were digitized from the video data. The ZVC is seen to be an effective metric of both vortex core position and relative strength. These measurements were made each 1/30 of a second for 12 seconds covering several cycles of oscillation. The complex correlation between the two time series showed hysteresis and phase lag. The dynamic characteristics are analyzed for the paper. By moving the stagnation point through a small range of angles, asymmetry could be created, corrected, and varied, at various rates.