Investigation of Turbulent Coherent Structures in the Separation and Reattachment of Flow behind a Swept Backward-Facing Step

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In the present study, the flow over a swept backward-facing step has been investigated experimentally and numerically. Measurements were made by single hot-wire and flying hot-wire (referred to as FHW) techniques. In order to confirm the applicability of the FHW in the spanwise direction, the standard turbulent boundary-layer was examined by comparing with a hot-wire rake. Mean and fluctuating velocity distributions were measured in the flow separated from a sharp edge, and compared with those in the turbulent boundary layer. The FHW was tried to capture the turbulent coherent structures in the spanwise direction. For two-dimensional backward-facing step flow, the relative step height to boundary layer thickness of an incoming flow were H/δ_0=0.5, 1.0 and 1.5. Mean and fluctuating velocity distributions for H/δ_0=0.5 and 1.0 were examined by a stationary hot-wire and flying hot-wire anemometer with I-type probe. Streamwise distributions of the forward-flow fraction, γ, near the wall were calculated, and then reattachment points of the separating flow were evaluated as a location of γ=50%. In the range of H/δ_0=0.5 to 1.5 in the present study, the reattachment length is almost constant.