Direct Numerical Simulation of Transition and Turbulence in Magnetohydrodynamic Flows in Rectangular Ducts

Abstract

In this work, a flow of an electrically conducting fluid is driven through a rectangular duct by a constant pressure gradient in the presence of a transverse, externally applied magnetic field: the flow is studied using the method of Direct Numerical Simulation (DNS). This particular Magnetohydrodynamic (MHD) flow investigation is important in the development of liquid metal blankets design, which is the proposed cooling system within nuclear fusion reactors. The duct walls parallel to the magnetic field are ideally electrically insulating, while the walls perpendicular to the magnetic field are ideally electrically conducting. This flow is referred to
as a Hunt’s flow. In this work the emergence of time dependent flow and its transition to a fully developed turbulent regime is explored. By fixing the strength of the magnetic field and
increasing the fluid velocity, a number of time-dependent flow regimes have been observed in the side layers, which includes Ting-Walker vortices, elongated vortical structures, fully
turbulent side-wall jets, as well as singular and multiple side-wall jet detachments.

It has been found that at low velocities, the time-dependant flow takes the form of Ting-Walker vortices, which develop in the side layers of the duct. For all but the lowest magnetic fields studied, the Ting-Walkers vortices completely disappear after a short initial transient time, being replaced by new, higher energy, complex, anisotropic vortical structures. Additionally, a number of new flow regimes involving jet detachment have been identified. This study also demonstrates that Hunt’s flow exhibits hysteresis behaviour, where different unsteady states are possible for the same flow parameters.

Date of Award	2016
Original language	English
Awarding Institution	Coventry University
Supervisor	Sergei Molokov (Supervisor)