Control of the three-dimensional separated-flow region down-stream of a swept, rearward-facing step has been studied with the purpose of reducing the separated-flow region and attendant drag. Results have indicated that geometric modifications in the region downstream of the step where the spanwise vortex is formed has little effect on the extent of the separated flow, while “conical-lip” and “vortex-trough” base modifications lead to a significant reduction in reattachment distances. The “conical-lip” modification involves a step lip with variable radius and the “vortex troughs” are grooves in the surface upstream of the step which produce longitudinal vortices.

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