The problem of flow past a bluff body at high Reynolds Number is one of the oldest in Hydrodynamics. Formally, it dates back to 1867 when Kirchhoff found a free-streamline representation of steady flow past a flat plate set normal to the oncoming flow. The drag coefficient, Cd = 0.88, is much too low because the model does not account for the negative pressure coefficient (suction) on the base of the body.

In the real flow the low base pressure is related to vigorous unsteady motions in the near wake due to vortex shedding. A different class of bluff-body flows is obtained by eliminating the vortex-shedding instability with a splitter plate in the near wake. This increases the base pressure and reduces the drag; the mechanics in the near wake is now governed by the unsteady motions ("turbulence") in the separated free shear layers.

In this seminar, a model is proposed for the latter class of flows, which includes flow past a downstream-facing step and also the classical, supersonic base-presure problem.