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 ${ \bf F} ({ \bf r})$.
Categories: physics.flu-dyn cond-mat.stat-mech