Studies on quasi-2D turbulence—the effect of boundaries

Abstract

This paper addresses the effects of domain boundaries on the behaviour of quasi-two-dimensional flows, thereby distinguishing between lateral boundaries of horizontal flow domains and the horizontal boundaries confining shallow fluid layers. As already discussed in some recent papers, the lateral walls may play an essential role in acting as sources of filamentary highamplitude vorticity, which usually affects the flow evolution in the interior of the domain. Besides, walls exert forces that may promote the self-organization of the flow, and hence contribute to a change in the net angular momentum of the flow. Both aspects will be reviewed briefly.In contrast to what is commonly assumed, shallow-layer flows may develop an essentially three-dimensional structure, with vertical gradients in the principal horizontal flow field and with significant vertical velocity components. These features have been found recently in experiments on electromagnetically generated flows in a shallow fluid layer. In this paper, we will discuss some of these experimental observations as well as some numerical simulation results that are helpful in explaining the observed flow dynamics.

Transient inverse energy cascade in free surface turbulence

“…The phenomenology of the split energy cascade changes in the presence of confining physical boundaries, as in the case of laboratory experiments performed in a thin layer of fluid confined by gravity [22][23][24]. The bottom (and lateral) boundary of the tank produces a boundary layer which dissipates a relevant fraction of the energy injected in the system [22,25] and thus reduces the turbulent flux, in particular in the case of a single layer of fluid [23]. Experiments with a double layer, in particular of immiscible fluids, reduce the damping rate induced by the bottom wall and produce an inverse cascade of energy [23,26].…”

Gyrokinetic Statistical Absolute Equilibrium and Turbulence

“…More recently, it has provided insights 22 into the unexpected phenomena of spontaneous "spin-up" in bounded 2-D fluid turbulence simulations. 23,24 (Interestingly, a current research topic in the fusion field is spontaneous rotation observed in tokamaks. 25,26 ) The most well-known result from this approach may be the prediction of inverse energy cascade in two dimensional turbulence by Kraichnan,27 following which Frisch et al 28 calculated the magnetohydrodynamic (MHD) absolute equilibrium and illustrated how the inverse cascade of magnetic helicity may help explain the generation of large-scale magnetic fields in some astrophysical systems.…”