Direct measurements of anisotropic energy transfers in a rotating turbulence experiment

Abstract

We investigate experimentally the influence of a background rotation on the energy transfers in decaying grid turbulence. The anisotropic energy flux density, ${\bf F} ({\bf r}) = < δ{\bf u}\,(δ{\bf u})^2 >$, where $δ{\bf u}$ 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 $E({\bf r}) = < (δ{\bf u})^2 >$, in agreement with the Kármán-Howarth-Monin equation. Surprisingly, our results prove that this anisotropy growth is essentially driven by a nearly radial, but orientation-dependent, energy flux density ${\bf F} ({\bf r})$.