Magnetic suppression of cylindrical MHD couette flow vortex

Abstract

Combining the classical fluid mechanics and the theory of electromagnetism, present study based on a computational study has successfully investigated the flow pattern of a magnetic fluid in an annular space under the influence of an axial magnetic field. A magnetic fluid is filled into the three-dimensional annular space subjected to a condition where the inner cylinder rotates at a prescribed speed while the outer cylinder is stationary. The upper and lower axial boundaries are assumed symmetrical. The parameters studied include the inner rotational speed, the radius of the inner cylinder, and the strength of the external magnetic field, which is indicated by Hartmann number (Ha). When Ha = 0, the external magnetic field is absent, present study found that the swirl flow is stable at an inner rotational speed of 3 rad/s and flow instability kicks in at 4 rad/s when the radii of the inner and outer cylinders are 10 and 20 cm. As Ha increases, the onset of flow instability has been sufficiently delayed. Based on previous studies, it has been widely accepted that the presence of Lorentz force promotes the fluid element reluctance to flow. Along with this reasoning, the magnetic field is expected to stabilize the flow. This fact has been proven by the cases when Ha = 100. The flow fields in all cases considered show that the axial velocity component has been greatly eliminated. Another critical factor influencing the Taylor-Couette flow instability is the gap between the inner and outer cylinders. This study also shows that a greater value of this gap helps stabilizing the flow.