It is well-known that magnetohydrodynamic (MHD) flows behave differently from
conventional fluid flows in two ways: the magnetic field makes the flow field
anisotropic in the sense that it becomes independent of the coordinate parallel
to the field; and the flow of liquid across the field lines induces an electric current,
leading to ohmic damping. In this paper, an experimental study is presented of the
long-time decay of an initially three-dimensional flow structure subject to a steady
magnetic field, when the ratio of the electromagnetic Lorentz forces to the nonlinear
inertial forces, quantified by the magnetic interaction parameter, N0, takes large as
well as moderate values. This investigation is markedly different from previous studies
on quasi-two-dimensional MHD flows in thin layers of conducting fluids, where only
Hartmann layer friction held the key to the dissipation of the flow.The initial ‘linear’ phase of decay of an MHD flow, characterized by dominant
Lorentz forces and modelled extensively in the literature, has been observed for the
first time in a laboratory experiment. Further, when N0 is large compared to unity, a
distinct regime of decay of a vortex follows this linear phase. This interesting trend
can be explained in terms of the behaviour of the ratio of the actual magnitudes
of the Lorentz to the nonlinear inertial forces – the true interaction parameter – which
decreases to a constant of order unity towards the end of the linear phase of decay,
and remains invariant during a subsequent ‘nonlinear’ phase.
Two-dimensional Numerical Simulation on Performance of Liquid Metal MHD Generator