Features of the circulation arising while sinking from the surface of a finite volume of water with negative buoyancy

The study of the dynamics of the near-surface layer of water when sinking from the surface of a finite volume of water with negative buoyancy (or the thermal) is performed by using qualitative experiments in the hydrodynamic flume and numerical simulation of the phenomenon under study. Laboratory experiments have demonstrated vortex and highly unsteady nature of the flow of the density-inhomogeneous water generated by immersion from the surface of the final volume of water with negative buoyancy. All usually observed stages of transformation of the shape of water thermal were recorded in laboratory – the “mushroom”, the vortex ring and its decay. Numerical simulation confirmed vortex and shortlived nature of the emerging flow and allowed for detalisation the processes of immersion of the finite volume of salt water in a fresh environment. The use of three additional model fields of neutrally buoyant tracers made it possible to track the variability of the shape of the thermal, as well as the processes of mixing and involvement of fresh water into the motion. Detalisation of vertical circulation in the vicinity of the sinking thermal showed the presence of upward movements of fresh water on its periphery. In natural conditions, this circumstance should prevent for some time the possibility of generation of the next thermal at the given location of the sea surface.

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