Suppression of turbulence by mean flows in two-dimensional fluids

A review of recent experimental studies of turbulence suppression by mean flows in quasi-two-dimensional fluids is presented. Large-scale mean flows develop during spectral condensation of 2D turbulence as a result of the inverse energy cascade in spatially bounded flow. The spectral energy which is accumulated at the largest scale supports the mean flow which in turn affects turbulence. We show that such a flow can reduce the energy flux in the inverse energy cascade range via shearing and sweeping of the turbulent eddies. The former mechanism is more efficient at larger scales, while the latter acts on the smaller scales. Similar suppression of turbulence has been found in the presence of externally imposed flows. Turbulent (inverse energy) cascade is reduced in the presence of imposed flow, but still supports Kolmogorov-Kraichnan k −5/3 power law spectrum in the energy range.