Characterization of the Magnetized Free Shear Layer in Liquid Metal Flow

The free shear layer is a thin region where fast-moving fluid meets slower fluid, producing a sharp velocity gradient. While magnetic fields have little effect in everyday fluids, in conducting media like liquid metals and plasmas, they strongly influence flow through magnetohydrodynamic (MHD) interactions. We study this using liquid gallium, whose properties resemble plasma, making it well suited for exploring shear-driven MHD flows relevant to fusion and astrophysics. In our experiment, concentric metal cylinders rotate independently with liquid gallium filling the gap, and split endcaps create differential rotation near the boundaries. Axisymmetric steady-state simulations reveal a magnetized free shear layer at the midplane, consistent with theoretical predictions under specified boundary conditions. Near the endcaps, axial gradients dominate, producing thin Hartmann layers with spatial dependence, indicating radial–axial coupling not captured by simpler models. These findings demonstrate how applied magnetic fields restructure shear flow in conducting fluids, providing insights into magnetorotational instability (MRI), angular momentum transport, and boundary layer formation in MHD systems relevant to both laboratory experiments and astrophysical environments.