Flow visualization around a circular cylinder near to a plane wall

Abstract Flow visualization, particle image velocimetry and hot-film anemometry have been employed to study the fluid flow around a circular cylinder near to a plane wall for Reynolds numbers, based on cylinder diameter, between 1200 and 4960. The effect of changing the gap between the cylinder and the wall, G , from G =0 (cylinder touching the wall) to G / D =2, was investigated. It is shown that the flow may be characterized by four distinct regions. (a) For very small gaps, G / D ≤0·125, the gap flow is suppressed or extremely weak, and separation of the boundary layer occurs both upstream and downstream of the cylinder. Although there is no regular vortex shedding, there is a periodicity associated with the outer shear-layer. (b) In the “small gap ratio” region, 0·125 G / D G / D G / D >1·0, there is no separation of the wall boundary layer, either upstream or downstream of the cylinder.