Flow Induced by a Pair of Line Vortices Moving against a Circular Cylinder

A combined numerical and experimental analysis has been carried out for investigating the behavior of a pair of line vortices, mutually propelled to approach a circular cylinder. The flow is assumed to be two-dimensional in numerical simulations, and which condition is examined carefully in laboratory experiments. The Reynolds number R e =κ/ν based on the initial circulation κ of the vortices and the kinematic viscosity ν of the fluid ranges from 100 to 1500. Flow behaviors are identified and classified into three patterns with six types of characteristic trajectories associated with the primary and secondary vortices. Of particular interest are the phenomena of rebound and reversal, exhibited respectively by the primary vortices moving against the cylinder under different flow conditions. Stable pairs of line vortices are generated in laboratory experiments; flow visualization shows excellent agreement with numerical results in the comparisons of several flow behaviors.