Open-surface MHD flow over a curved wall in the 3-D thin-shear-layer approximation

Abstract

3-D thin-shear-layer equations for flows of conducting fluids in a magnetic field have been derived in orthogonal body-oriented coordinates and then applied to the analysis of MHD open-surface flows over a curved wall. Unlike the classic boundary-layer-type equations, present ones permit information to be propagated upstream through the induced magnetic field. Another departure from the classic theory is that the normal momentum equation keeps the balance between the pressure gradient term, and those related to gravity, centrifugal forces, and Lorentz force. Thus, the normal pressure variations are allowed. The model describes basic 3-D effects due to the wall curvature and spatial variations of the applied magnetic field. As a particular case, equations for flows with rotational symmetry have been derived. Numerical calculations were performed for open-surface flows over a body of revolution under conditions relevant to a fusion reactor (Hartmann number is 8500). Some specific flow patterns, such as flow thickening and spiral-type flows, have been observed and discussed. A special attention has been paid to the analysis of the magnetic propulsion as a tool for the active flow control by applying an electric current. It has been shown that depending on the applied current, the axial pressure gradient can act as an adverse pressure gradient or propulsion force.