A Study of Periodic Flow Behavior Over Backward Facing Step in Low Reynolds Number

Abstract

A study on the low Reynolds number flow such as the flow in or around the downsized device is strongly required along with the development of the micro manufacturing technology. It is important to clarify the flow behavior of the separating shear layer in small channel or around small device. The low Reynolds number flow over a backward facing step is selected as an example of the recirculation vortex in the present study, because the mixing promotion is expected from an oscillatory motion of the vortex in the separating and reattaching shear layer by the step edge. The Reynolds number based on step height is set at 130 to 3700 in the micro sensing wind tunnel. The behavior of the near wall flow is measured by Micro Flow Sensor (MFS), and the flow field is visualized with a high-speed video camera. The results show that the frequencies of 36 Hz and 24Hz appear in the flow on the lower and upper wall downstream of the step. To identify the periodic motion near the wall, the dominant frequency of the separating shear layer is analyzed by the linear instability theory.