Flows over two-dimensional backward-facing steps

This paper presents experimental results on the mean and turbulence velocity fields for flow over two-dimensional backward-facing steps in ducts and open channels. The dependence of the flow on the upstream Reynolds number and on the expansion ratio is investigated. Where possible, comparisons have been drawn between these results and those of other researchers. The experiments were carried out in water flows in nominally two-dimensional test sections. Velocity measurements were made with a single-component, laser-Doppler anemometer operated in forward scatter and employing a transient recorder and digital computer for signal processing. Measurements were obtained for Reynolds numbers (based on step height) in the range 2,000-20,000, and for expansion ratios in the range between 1.06 and 3.0.