Dynamics of pancake-like vortices in a stratified fluid: Experiments, model and numerical simulations (Q2726656)

Dynamics and structure of pancake-like isolated monopolar vortices in a linearly stratified non-rotating fluid is investigated by laboratory experiments and numerical simulations. The distribution of the vertical component of vorticity has been measured, as well as the vertical density profile through the centre of vortex. The laboratory experiments confirm that inside the vortex the density profile is deformed. To describe the decay of the vortex due to viscous diffusion only, the authors propose a diffusion model which they derive from Boussinesq equations under the assumption of a purely axisymmetric swirling flow inside the vortex. Numerical simulations are performed based on time-dependent Navier-Stokes equations in Boussinesq approximation. Thise equations are discretized by a central second-order finite difference scheme on a staggered grid in a cylindrical coordinates, and are solved by fractional step method. It is shown that the vortex decay is accompanied by a buoyancy-induced second circulation. The vortex therefore becomes stretched during its decay. Under flow conditions in laboratory experiments, the stretching effect is almost negligible, and the vortex decay can be described well by the diffusion model.