A flow visualization study of the development of vortex structures in a round jet impinging on a flat plate and a cylindrical pedestal

Smoke-wire flow visualization is employed to investigate the behavior of a round jet issuing from a straight tube and impinging on a cylindrical pedestal mounted on a flat plate. Velocity and turbulence intensity measurements at the jet exit show correlation with the formation of visualized structures near the impingement surface. The effects of jet exit-to-surface spacing (H/d) and Reynolds number (Re) are explored. It is found that as jet exit-surface spacing increases from 2 to 5, small but significant effects can be seen. These effects include a stabilization of the flow, a lengthening of the potential core and a reduction in vortex formation prior to impingement. An increase in Re is found to increase the turbulence in the shear layer and suppress vortex formation. The presence of the cylindrical pedestal is found to stabilize the jet prior to impingement and also creates a recirculation region at the edge of the pedestal for low Re.