Experimental study of liquid metal channel flow under the influence of a nonuniform magnetic field

We present an experimental study of a liquid metal flow in a rectangular channel under the influence of an inhomogeneous magnetic field. This is a fundamental problem of liquid metal magnetohydrodynamics that is relevant to the technique of electromagnetic braking in the process of continuous casting of steel as well as for Lorentz force velocimetry. Based on local velocity and electric potential measurements we identify three distinct flow regions; namely (i) a turbulence suppression region, (ii) a vortical region, and (iii) a wall jet region. It is shown that in region (i) the applied inhomogeneous magnetic field brakes the incoming flow in its central part and transforms the velocity profile, which is initially flat, into an M-shaped form. In the central part of the flow, the intensity of the velocity fluctuations is found to decrease strongly. In region (ii) where the magnetic field is strongest, the flow is characterized by large-scale vortical structures which are time dependent for certain values of the control parameters. In region (iii), downstream of the magnetic system, two sidewall boundary layers are observed which generate velocity fluctuations with intensity up to 25% of the mean flow. These boundary layers bear close resemblance to wall jets known from ordinary hydrodynamics. Our experimental data provide a comprehensive database against which numerical simulations and turbulence models can be tested.