Formation of vortex streets in shear flow

Abstract

Main features of the formation of vortex streets from the free shear layers emanating from two-dimensional bluff bodies placed in shear flow are obtained by means of the Abernathy-Kronauer model which is extended to include the effect of the background vorticity on the vortex formation. The calculations show that the background vorticity promotes the rolling up of the vortex sheet of the same sign whereas it decelerates that of the vortex sheet of the opposite sign. The vortex clouds in the low-velocity side of shear flow fall behind and will eventually be overtaken by the vortex clouds in the high-velocity side. Thus the steady configuration of the conventional Karman vortex street is no longer possible in shear flow. These features of the theoretical vortex patterns are experimentally verified by a flow-visualization technique.