The starting flow down a step

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Abstract
The incompressible starting flow past a downstream-facing right-angled step was investigated at Reynolds numbers R (based on step height) less than 500 by means of flow-visualization techniques. The distance between the step and the point of reattachment on the downstream wall was found to increase linearly with time at intermediate stages of the flow development. The recirculation region formed behind the step was composed of three vortex domains at earlier stages of its development when R [gap ] 140. It was observed for R [gap ] 200 that once the starting vortices had been shed downstream a steady recirculation region was established. The evolution of filaments of tracer in the flow down the step was found to vary considerably with R. The filaments were observed to develop faster in the flow down the step than in that past a symmetric model without a downstream wall when R [gap ] 140.