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When a moving surface slides under a stationary one, the potential exists for
a vortical structure to develop close to the junction if the velocity
of the moving surface is sufficiently high. The mechanism for the formation
of this structure is the convection of the boundary layer material formed
on the moving wall over the stationary plate. This results in an unsteady
wall jet on the stationary plate that separates and rolls into a vortical
structure as shown in the figure. Experiments show that a centrifugal instability
develops along the vortex core which results in the eventual turbulent
breakdown of the structure.
Contributed by Prof. James Allen,
New Mexico State University, Los Cruces, NM, U.S.A.
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