Topical Problems of Fluid Mechanics


Institute of Thermomechanics AS CR, v.v.i.	CTU in Prague Faculty of Mech. Engineering Dept. Tech. Mathematics	MIO Université du Sud Toulon Var - AMU - CNRS - IRD	Czech Pilot centre ERCOFTAC

Stability of a Conducting Fluid Contained Between Two Rotating Spheres Subjected to a Dipolar Magnetic Field
A. Lalaoua, F. Naït Bouda, A. Merah
Abstract:
The motion of fluid enclosed between two concentric rotating spheres, so-called the spherical Couette flow, presents a wealth of phenomena encountered during laminar turbulent transition, depending on the gap width and the Reynolds number. In the case, where the fluid is taken as an electrically conducting, and a magnetic field is imposed, knows as magnetic spherical Couette flow, the flow behaviour and pattern formation can be drastically changed. This flow problem offers the possibility of exploring a wide variety of instabilities and plays an important role to understand the geophysics and astrophysics phenomena as well as to study the dynamics of the Earth’s outer core. In this paper, the flow of an electrically conducting fluid, liquid sodium, in an annulus between two concentric rotating spheres subjected to a dipolar magnetic field is investigated numerically using a three-dimensional computational fluid dynamics. The outer sphere is stationary while the inner one rotates freely about a vertical axis passing through its center. The spherical shell is completely filled with liquid sodium. The numerical studies are performed for the medium gap width β = 0.18, and carried out for a wide range of Hartmann number, Ha, from 0 up to 5000. Both inner and outer spheres are considered insulating walls. Computations for the onset of Taylor vortices in spherical Couette flow without an imposed magnetic field show a good agreement with the previous works. It is established that the imposed magnetic field radically alters the flow structures leading to significant topological changes on the flow patterns. In particular, we found that depending on the magnetic field imposed, the basic state consists of either a shear layer or a counter-rotating jet and both becoming thinner and thinner for increasingly strong imposed fields, but with the jet also becoming stronger.
Keywords:
CFD simulation, Spherical Couette flow, Taylor vortices, Dipolar magnetic field, instability, Conducting fluid

Fulltext: PDF DOI: https://doi.org/10.14311/TPFM.2017.025

In Proceedings Topical Problems of Fluid Mechanics 2017, Prague, 2017 Edited by David Šimurda and Tomáš Bodnár, pp. 195-202 ISBN 978-80-87012-61-1 (Print) ISSN 2336-5781 (Print)