Experimental investigation of the flow around a surface mounted block.

摘要

Flow in the symmetry plane of a surface mounted block is studied experimentally by means of Digital Particle Image Velocimetry for three Reynolds numbers based on the block height (Re_a = 500, 1000, 2500) and two channel widths $Ha$ = 1.825 and 4.6. Instantaneous, mean and fluctuating velocity fields of the separated shear layers upstream, over the top and in the wake of the block have been acquired and analyzed.; For the lowest Reynolds number studied, velocity measurements indicated that the flow was steady and exhibiting laminar characteristics upstream, over the top and in the near wake region for both of the channel widths. A steady system of horseshoe vortices was identified upstream of the block for the lowest Reynolds number. There was no vortex shedding observed for the flow over the top of the block and the recirculation region was found to be very thin.; For the two higher Reynolds numbers, the flow was unsteady upstream of the block for both of the channel widths. The number of vortices in the horseshoe vortex system was found to increase with increasing Reynolds number and this was consistent with the observations of previous researchers. The highest normal Reynolds stress measurements were found at the center of the primary horseshoe vortex for the flow upstream of the block. Flow over the top of the block was found to be relatively unsteady with higher Reynolds stress values as compared with the lowest Reynolds number. The recirculation region thickness was observed to increase with increasing Reynolds number and increasing channel width. The highest Reynolds stress magnitudes were found just outside of the Ū = 0 contour line for this region. The recirculation height for the flow over the top of the block was an appropriate length scale. As for the flow in the wake region, mean velocity characteristics and the reattachment lengths for the two higher Reynolds numbers were similar.; The effect of the three dimensionality were investigated by calculating symmetry plane flow rates as a function of streamwise distance and in the wake, by comparison with 2-D backward facing step flow. It was seen that three dimensionality significantly affects the flow throughout the measurement domain.