HAIR-PIN VORTICES FROM THE COMBINED WAKE OF TWO RECTANGULAR CYLINDERS AT A LOW REYNOLDS NUMBER

Experiments are conducted to study the wake flow patterns of two rectangular cylinders at a Reynolds number of 292. The cylinders are parallel to the flow direction. The gap ratio between the cylinders, dss/w, is fixed to 0.4/1. The results show that lifted streamlines inside the gap between the cylinders are entrained into a series of hair-pin vortices at farther downstream locations. The hair-pin vortices are formed from the combined wake of the cylinders and are lifted farther away from the bottom wall while they are being swept downstream. The scale of the hair-pin vortices is relatively large as compared to the boundary layer thickness of the incoming flow.