PIV Investigation of Reynolds Number Effects on a Closed Channel Flow Over a Smooth Forward Facing Step

This paper presents an experimental investigation of Reynolds number effects on the characteristics of separated and reattached flow over a smooth forward facing step. Particle image velocimetry technique was used to conduct detailed velocity measurement for a wide range of Reynolds numbers based on the step height and freestream velocity, 2040≤Re_h≤8750. For each test case, the aspect ratio, AR = 21, ratio of boundary layer to step height, δ/h = 2.6 ± 0.2 and freestream turbulence level of 4% were kept constant. The results showed that the reattachment length increased monotonically with increasing Reynolds number for Re_h < 6000, beyond which the reattachment length was independent of Reynolds number. In the recirculation region on top of the step, the Reynolds normal stresses were independent of Reynolds number but a higher Reynolds number increased the Reynolds shear stress in the region adjacent to the top of the step.