"Vortical Flow Control Using a Moveable Stagnation Point"
L.A. Darden and N.M. Komerath
American Physical Society, November, 1994
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.