Vortex shedding from a square cylinder near a wall

Wake velocity and cylinder pressure measurements are used to investigate the changes in the vortex shedding from a square cylinder near a solid wall at a Reynolds number of 19 000. The phase-averaged velocity field shows that vortex formation is displaced downstream due to the presence of the wall. Reattachment of the shear layer on the lower cylinder face interrupts the coupling of the upper and lower shear layers so that suppression of vortex shedding occurs for a gap height to diameter ratio, S/D < 0.4. Circulation ratios at suppression are consistent with the extension of von Kármán's stability analysis for two rows of alternating vortices of unequal strength. It is observed that vortex shedding becomes increasingly intermittent for gap height ratios below 0.5 as a result of the straightening of the separated shear layers and reduced coupling between them.