Postdoc: Interaction between a vortex and a fluid interface

Fluid vortices in environmental and engineering flows exist over a large range of scales, from huge tornadoes, through tip vortices in the wake of turbines, to the smallest eddies in turbulent regions at dissipation scale. Many situations involve vortical flows in which several immiscible fluids are present. They include floating bodies or bodies immersed at small depth which shed vortices under the water surface, or propellers and foils in the wake of which tip vortices may cavitate or simply trap atmospheric air into their core. In these instances, the presence of a liquid/gas interface located either in the vicinity of the vortex or within its core, significantly modifies its dynamics. Fundamental studies on the interplay between vorticity and interfaces are rare. The work proposed will investigate the interaction of a single fluid vortex and a liquid/gas interface in various configurations through theoretical/numerical modelling and stability analyses. The configurations include:

• a horizontal fluid vortex below an external liquid/gas interface;
• a fluid vortex with a gas cavity in the axis region, i.e., a two-phase vortex, where the only interface is located inside the vortex core;
• a two-phase vortex below an external liquid/gas interface.

Quasi-steady solutions will be derived for these configurations, and their stability with respect to long- and short-wave vortex perturbations will be investigated. The results will be compared to those obtained from water channel experiments and numerical simulations carried out by other participants in this project.