Reconnection of two vortex rings

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Abstract
The reconnection of two identical viscous vortex rings is investigated numerically. The initial state consists of two rings (of Re≡Γ/ν=578) of a circular cross section placed side by side in a periodic box with their coplanar axes inclined by 30° to the symmetric plane. The subsequent motion is examined by solving the Navier–Stokes equation by a dealiased pseudospectral method in a 643 box. We found two prominent reconnection processes: first, the two vortex rings merge into one by viscous annihilation of opposite vorticity and second, two new rings, which are connected by two ‘‘legs,’’ are created by bridging. The apparent differences with laboratory experiments are discussed.