Some physical aspects of separation bubble on a rounded backward-facing step

Reported are some results of a study on the local separated flows around a rounded backward facing step. Experiments were carried out in a water tunnel (WSG) with outstanding inflow qualities. Flow visualizations using hydrogen bubble along with laser sheet lighted particles were applied. The Reynolds numbers for the present results are from 8×103 to 1×105 based on the length Lp of the front flat plate and incoming flow velocity. Velocity measurements were performed with video-based particle image velocimetry (PIV) at sampling frequency of 25 Hz. Evaluation on both flow visualization and PIV data reveal that the local separated region is dominated by dynamic vortex systems with strong periodic features. The separation exhibits an open bubble type in topology with intense interaction with outer flow. Also discussed are the wave like development of vortices in the sense of deformation as well as the resulted Λ-formed coherent structures.