Robust inverse energy cascade and turbulence structure in three-dimensional layers of fluid

TL;DR

This study demonstrates the existence of inverse energy cascade in thick fluid layers with predominantly 3D turbulence, showing that surface conditions can induce quasi-2D behavior and spectral condensates.

Contribution

First experimental evidence of inverse energy cascade in 3D-dominated flows, revealing surface-induced quasi-2D turbulence and flow planarity in layered fluids.

Findings

Inverse energy cascade occurs in thick fluid layers with 3D turbulence.

Surface conditions can induce quasi-2D behavior supporting inverse cascade.

Spectral condensates can form and suppress 3D eddies in the flow.

Abstract

Here we report the first evidence of the inverse energy cascade in a flow dominated by 3D motions. Experiments are performed in thick fluid layers where turbulence is driven electromagnetically. It is shown that if the free surface of the layer is not perturbed, the top part of the layer behaves as quasi-2D and supports the inverse energy cascade regardless of the layer thickness. Well below the surface the cascade survives even in the presence of strong 3D eddies developing when the layer depth exceeds half the forcing scale. In a bounded flow at low bottom dissipation, the inverse energy cascade leads to the generation of a spectral condensate below the free surface. Such coherent flow can destroy 3D eddies in the bulk of the layer and enforce the flow planarity over the entire layer thickness.