Turbulence anisotropy and coherent structures in electromagnetically generated vortex patterns

Abstract

Numerical investigations addressing influence of the localised electromagnetic forcing on turbulent thermal convection of a weakly electrically conductive fluid in a wall-bounded rectangular enclosure are performed over a wide range of working parameters (104≤Ra≤5×10 5, Pr=7). An asymmetrical electromagnetic forcing (EMF) is applied originating from combined effects of the imposed magnetic fields (originating from an array of 5x7 permanent magnets with |b0|max=1 T each, located beneath the lower thermally active wall) and electric fields (originating from two electrodes supplied with dc current of different intensities, 0≤I≤10 A). Subgrid turbulent stress is modelled by electromagnetically extended Smagorinsky model and subgrid turbulent heat flux is represented by a simple gradient diffusion hypothesis. Simulations revealed two interesting findings: the electromagnetic forcing generated significant overall heat transfer increase (more than 500% for lower values of Ra) compared to its neutral case, and, the turbulence anisotropy was reduced in the central part of the enclosure.