Reconnection of counter-rotating vortices

Reconnection of counter-rotating vortices. Two initially almost rectilinear counter-rotating vortices usually reconnect one to the other, and form two loops on each side of the reconnection region. This phenomenon can be observed in the sky in the wake of airliners. More generally, it is a generic process of fluid motion. Vortex reconnection can be investigated through numerical simulations. The two vortices are locally compressed one towards the other, they become smaller (they can be seen in the middle of the picture), are stretched and rolled up around the newly formed loops, and eventually dissipate. The picture shows a surface of constant vorticity, colored by pressure. The reconnection region (in red) is a high-pressure zone. The pressure gradient occuring between the red and the green region generates axial velocity in the vortices.