Flows over backward-facing steps with different spanwise widths

The effect of spanwise aspect ratio ($A\phantom{\rule{0}{0ex}}R$) on flow characteristics over backward-facing steps with extended streamwise length and external corners is investigated experimentally. For intermediate $A\phantom{\rule{0}{0ex}}R$, a unique wake pattern is observed, where there is no separation bubble, and the flow after reattachment ejects from, rather than impinging on, the central plane bottom floor, leading to intensified fluctuations and a broader region of high turbulence. This flow feature may be attributed to strong interactions of separated flows from all open edges with possible contributions from corner vortices that develop alongside the step. We also discuss the influence of these corner vortices for varying $A\phantom{\rule{0}{0ex}}R$.