Vorticity and Capillaries at the Surface of a Jet

TL;DR

This study investigates shear layer instability at a water jet's surface, revealing how capillary waves form and inject vorticity, leading to vortex pair formation through experimental visualization techniques.

Contribution

It provides new experimental insights into the mechanisms of capillary wave formation and vorticity injection at a water jet surface.

Findings

Capillary waves form due to shear layer roll-up.

Vorticity is injected into the flow through wave collisions.

A counter-rotating vortex pair develops and moves downstream.

Abstract

Shear layer instability at the free surface of a water jet is studied. The accompanying video shows experimental data recorded using measurement methods such as Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocity (PIV). These results reveal the mechanisms leading to the formation of capillary waves on the surface due to the roll-up of the shear layer. These capillary waves eventually collide to each other, injecting vorticity in the bulk of the flow. Shear layer and injected vorticity interact to form a counter rotating vortex pair that moves down to the flow.