Abstract
Energy transfers are characterized in a rotating turbulence experiment from the analysis of the second and third order structure functions, measured in the plane normal to the rotation axis by means of particle image velocimetry. Departure from the von Karman-Howarth equation are systematically analysed, both in a freely decaying and in a forced configurations. In the decaying case, a change of sign of the 3rd order SF is observed, at a scale r0 which decreases in time. The local Rossby number at this scale r0 is found to be approximately constant during the decay, of order of 0.1. Although this sign change for the nonlinear term suggests the onset of an inverse energy cascade at large scales, this effect is hidden at large times by the viscous contribution, and no net energy accumulation could be observed at large scales in the decaying case. On the other hand, in the continuously forced case, a steady state is obtained, with a double energy cascade fed at intermediate scale by the forcing.
Related Links
- http://www.fast.u-psud.fr/~moisy/turbrot/turb_en.php - Web page of the experiment