3D Visualization of Reconnections in Vortex Ring Collision

Vortex interactions appear in many fluid systems, from the wake behind an airplane in flight to that of a ship moving through the water. This is because friction between a fluid and a solid boundary can generate vorticity in the fluid. A simple example is the vortex ring, yet even the interaction between two vortex rings can cause instabilities that break the symmetries of the flow. When two vortex rings of equal size collide head-on at moderate Reynolds number, the rings undergo an instability that brings the two vortex cores together at several points around the circumference of the rings. As the two vortex cores touch, there is an annihilation of the opposing vorticity from each ring which results in reconnection between the original two vortex rings. These reconnections have a complicated 3D structure that is difficult to measure experimentally, leading many studies to focus on numerical simulation. By scanning a laser sheet across the collision of two dyed vortex rings, we are able to reconstruct a tomographic 3D visualization of the vortex ring collision and reconnection as it occurs. This 3D visualization allows for comparison between the structure of reconnections in experiment and the predictions from numerical models.