The effect of aspect ratio on the flow over a rearward-facing step

In this study, we investigate the effect of the spanwise width on the mixing layer behind a rearward-facing step. Results for aspect ratios (tunnel width/step height) of 10 and 4 and Reynolds numbers of 11,000 and 5,000 are presented. A frequency shifted, single component LDV system was used to obtain mean streamwise velocity profiles, turbulence intensity profiles, and normal velocity spectra at four streamwise and three spanwise positions for each test case. The mean velocity and turbulence intensity profiles are constant across the width of the test section for either of the Reynolds numbers considered, but there are significant differences among the cases studied. At a distance greater than three step heights down-stream of the step, the peak turbulence intensity is greater for higher aspect ratio and is relatively insensitive to Reynolds number. The peak frequency is lower and the spectrum is narrower for a higher aspect ratio in the region near the step.