Surface roughness effects on separated and reattached turbulent flow in open channel

Experimental research was carried out to study surface roughness effects on the characteristics of turbulent flow downstream of a backward facing step in an open channel. Particle image velocimetry measurements were conducted over sand grain roughness and a reference smooth surface downstream of the backward facing step. The experiments were conducted at a Reynolds number of 3240 based on the step height and freestream velocity of the approach flow. The vorticity thickness, streamwise mean velocity, Reynolds stresses, triple velocity correlations and two-point correlation coefficients were obtained to quantify surface roughness effects in the separated region through to the recovery region. The results demonstrated that roughness effects on the flow characteristics are evident only in the recovery region.