Three-dimensionality in quasi-two dimensional flows: recirculations and barrel effects

TL;DR

This paper proposes a unified scenario explaining the emergence of three-dimensional recirculations and effects in quasi-2D flows, such as rotating and MHD flows, highlighting their boundary layer origins and implications across various disciplines.

Contribution

It introduces a novel, unified explanation for 3D effects in quasi-2D flows, emphasizing boundary layer mechanisms and cross-disciplinary relevance.

Findings

3D recirculations originate in wall boundary layers.

Boundary confinement alone does not trigger 3D effects.

The scenario applies to rotating, MHD, atmospheric, and oceanic flows.

Abstract

A scenario is put forward for the appearance of three-dimensionality both in quasi-2D rotating flows and quasi-2D magnetohydrodynamic (MHD) flows. We show that 3D recirculating flows and currents originate in wall boundary layers and that, unlike in ordinary hydrodynamic flows, they cannot be ignited by confinement alone. They also induce a second form of three-dimensionality with quadratic variations of velocities and current across the channel. This scenario explains both the common tendency of these flows to two-dimensionality and the mechanisms of the recirculations through a single formal analogy covering a wide class of flow including rotating and MHD flows. These trans-disciplinary effects are thus active in atmospheres, oceans or the cooling blankets of nuclear fusion reactors.