Direct Measurements of Anisotropic Energy Transfers in a Rotating Turbulence Experiment

We investigate experimentally the influence of a background rotation on the energy transfers in decaying grid turbulence. The anisotropic energy flux density F(r)=⟨δu(δu)²⟩, where δu is the vector velocity increment over separation r, is determined for the first time by using particle image velocimetry. We show that rotation induces an anisotropy of the energy flux ∇·F, which leads to an anisotropy growth of the energy distribution E(r)=⟨(δu)²⟩, in agreement with the von 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 F(r).