Near surface flow patterns of two rectangular cylinders at a low reynolds number

Experiments are conducted to study near surface flow patterns of two rectangular cylinders at a Reynolds number of 292. Two configurations of the cylinders are investigated; namely, one parallel and the other perpendicular. The gap ratio between the cylinders, dss/w, varies from 0 to 1/1 and 0 to 1.2/2 for the former and latter case, respectively. The results indicate that streamlines inside the gap between the cylinders are lifted up as they pass through the gap, irrespective of flow configurations. The flow coming out of the gap is biased toward the wake of one of the cylinders when dss/w is small. Flow bias occurs in both types of flow configurations, causing one of the wakes being smaller. However, in the perpendicular flow configuration, the flow bias occurs at a smaller gap and prevails to a larger gap. In addition, the horseshoe vortex is flatter and at a position closer to the front faces of the cylinders and fluid particles can still move upstream from the downstream side toward the leeside of the cylinders at larger gaps.