The flowfield produced by a pair of rectilinear vortices approaching a circular cylinder was experimentally investigated by means of smoke visualization technique. The growth of the shear layer separated from the cylinder surface, the separation point, the generation of the secondary rectilinear vortices and the location of the centers of the main vortices could be observed using cigarette smoke.
It was found that the trajectories of the vortices were bent laterally due to the velocity induced by the separated shear layer and the resulting secondary vortices. It could not be observed in our experiments for a pair of rectilinear vortices to pass around a circular cylinder, while a ring vortex can pass around a sphere.
The trajectories of vortices were bent earlier, but came nearer to the cylinder with increase in Reynolds number, which was defined by the traveling velocity of vortices and the distance between them.

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