An experimental investigation of the Kelvin-Helmholtz vortex generation between two fluids in shear

Shear layers occur at the interface between two fluids moving at different velocities, often producing flow instabilities. One common instability that develops under such conditions is the Kelvin-Helmholtz instability (KHI), which generates strong vorticity, turbulent mixing, and energy transfer. This instability is widespread in both natural and engineering flows, including oceanic and atmospheric currents, jets, and wakes. To generate KHI repeatably, a tilting tank was designed, built, and tested, allowing different fluid combinations to accelerate past each other in opposite directions. The results demonstrate effective methods for producing KHI, visualizing the instability using slow-motion and particle image velocimetry (PIV) software, and interpreting the resulting flow behavior for three fluid combinations. To investigate the influence of fluid properties, combinations with varying density, miscibility, and viscosity were selected: water and saltwater, water and vegetable oil, and water and vegetable glycerin. The water-saltwater system, with the smallest viscosity contrast, produced the most coherent Kelvin-Helmholtz waves, which grew in amplitude and wavelength as the flow accelerated before eventually breaking down into turbulent mixing. Consistent with previous studies, increased viscosity and surface tension dampen the instability.