Characteristics of the secondary vortex in the cylinder wake vortex/boundary layer interaction

The interaction between the wake vortex of the upstream-positioned cylinder and the flat plate boundary layer is investigated using flow visualization technique in the water tunnel.As a result of the inducement from the outer wake vortex,a secondary vortex is found emerging from the boundary layer,whose birth condition,generation mechanism and evolution type is carefully investigated.The result shows that the interaction between the wake vortex and the secondary vortex is the core phenomena to understand the vortex/boundary layer interaction.Moreover,a non-dimensional parameter yc/D is used to descript the influence of both the diameter and the normal position of the cylinder,which divides the vortex/boundary layer interaction into three regimes,characterising the variation of the cylinder wake vortex shedding St number,the rebound of the wake vortex,the generation of the secondary vortex and the different patterns of wake vortex/secondary vortex interaction.