LOW REYNOLDS NUMBER EFFECT ON OPEN CHANNEL FLOW OVER A RIB

摘要

An experimental study was conducted to investigate low Reynolds number effects on open channel flow over a transverse square rib. Particle image velocimetry technique was used to perform detailed velocity measurement in the upstream and recirculation region of a square rib of height, h = 12 mm. The Reynolds number based on the freestream velocity and rib height, Re_h = 1510, 2650 and 3950 and the ratio of the boundary layer thickness to step height, δ/h = 2.5 ± 0.2. The results showed that the reattachment length of Re_h = 2650 and 3950 increased by 5.7% compared with corresponding value of Re_h = 1510. The mean velocities were independent of Reynolds number in the recirculation region but at the reattachment point, Re_h = 3650 reduced the streamwise mean velocity and enhanced the wall-normal mean velocity in the region adjacent to the wall. The turbulent kinetic energy beyond the center of the recirculation region increased with increasing Reynolds number.