Abstract
The influence of the turbulent boundary thickness on the vortex dynamics in the wake of a wall-mounted rectangular cylinder (height-to-width ratio h/d = 4) is investigated experimentally for a Reynolds number of 12,000 and two boundary layers (BL) of thickness /d = 0.72 (natural BL) and 2.56 (tripped BL). The interaction between the horseshoe vortex system (HVS) and the shedding of large-scale wake structures is considered. Time-resolved PIV measurements are performed in the wall-obstacle junction region. New insight into the physics of these flows is gained from studying the spatio-temporal evolution of the vortical structures and their interaction. It is found that delta/d plays an important role in modifying the flow topology around the rectangular cylinder through the interaction between the horseshoe vortices and shed vortices. A proper orthogonal decomposition analysis shows that the dynamics of the HVS strongly affects the topology of the shed vortices near the wall for the tripped boundary layer. Both the backflow and the zero-flow modes of the HVS have particular influence on the symmetry of the horseshoe legs and its momentum content. A stronger effect of the HVS is present for the tripped BL close to the wall where the kinetic energy content of these two modes is higher as compared to the natural BL.