Generation of a vortex dipoleThese experiments examines the flow field in the region where a moving wall slides under a stationary one. This produces an interesting flow phenomena with relatively simple generation geometry. The data reveals that in the absence of an apparatus length scale, a vortical structure forms a the junction and appears to scale in a self-similar fashion. The transitional regime of vortex development is marked by the appearance of an instability on the perimeter of the vortical structure. The instability mechanism appears to be centrifugal in nature.
Reference:Instability of a junction vortex - J. J. Allen and T. Naitoh Submitted for review to the Journal of Fluid Mechanics (2002)
Click for cross-section movie Click for streamwise instability movie Click for a vorticity movie Top half of ring, moving right to left.