Gyre turbulence

In enclosed basins, all ocean currents display large-scale gyres with a western intensification. This pattern was elucidated in the 1950s through a linear two-dimensional model incorporating planetary vorticity gradients. Through numerical experiments on a nonlinear version of this model, we illustrate the persistence of these low-energy gyres in a turbulence regime exhibiting a constant dissipation rate as viscosity approaches zero. This persistence is enabled by the emergence of an out-of-equilibrium vortex gas that houses the majority of flow energy. This vortex gas, reminiscent of oceanic weather, originates from instabilities in western boundary currents, efficiently evacuating energy from the gyres. The interplay between coats and planetary vorticity gradients results in a short-circuit in the ocean energy cycle preventing condensation of the vortex gas at the domain scale. Credit to Miller, Deremble, Venaille.

Von Kármán street

The von Kármán street occurs when water flows past an obstacle, resulting in the periodic shedding of vortices. As the fluid encounters the obstacle, the boundary layer separates from the surface, creating a region of recirculating flow and vortices. This detachment of the boundary layer contributes to the formation of the von Kármán street, where alternating vortices are shed periodically on either side of the obstacle. This experiment undergoes a transition to turbulence when the Reynolds number gets bigger than a critical threshold. In this experiment, the intricate dynamics of vortex shedding in the wake of an obstructing body are illustrated through fluorescein visualization in a controlled laboratory setting. Credit to Gilbert, Bozetine.