Direct measurements of anisotropic energy transfers in a rotating turbulence experiment

TL;DR

This study experimentally measures how background rotation causes anisotropic energy transfers in turbulence, revealing that anisotropy growth is driven by a nearly radial, orientation-dependent energy flux density.

Contribution

First experimental determination of anisotropic energy flux density in rotating turbulence using Particle Image Velocimetry.

Findings

Rotation induces anisotropy in energy flux and distribution.

Anisotropy growth is driven by a nearly radial, orientation-dependent energy flux.

Results align with the Kármán-Howarth-Monin equation.

Abstract

We investigate experimentally the influence of a background rotation on the energy transfers in decaying grid turbulence. The anisotropic energy flux density, ${\bf F} ({\bf r}) = < \delta {\bf u}\,(\delta {\bf u})^2 >$, where $\delta {\bf u}$ is the vector velocity increment over separation ${\bf r}$, is determined for the first time using Particle Image Velocimetry. We show that rotation induces an anisotropy of the energy flux $\nabla \cdot {\bf F}$, which leads to an anisotropy growth of the energy distribution $E({\bf r}) = < (\delta {\bf u})^2 >$, in agreement with the K\'arm\'an-Howarth-Monin equation. Surprisingly, our results prove that this anisotropy growth is essentially driven by a nearly radial, but orientation-dependent, energy flux density ${\bf F} ({\bf r})$.