Experimental Study of Spherical Couette Flow in Magnetic Fluids : Torque Characteristics for Outer Sphere Rotation

Abstract

Experimental investigation was carried out in an attempt to obtain data and phenomenological explanation of spherical Couette flow in a magnetic fluid for the situation where the outer sphere rotates while the inner sphere is stationary. Data for torque characteristics were obtained when a magnetic field was imposed on the fluid, using a bar magnet which was situated in a stationary inner sphere. The torque increases when the intensity of the magnetic field is increased, resulting in an increase of the effective viscosity. The rate of torque increase caused by the magnetic field is greater for larger gap width. The regime in which main flow is dominant (the simple linear Couette flow with negligible weak secondary flow) appeared to be extended with an increase of Reynolds number, suppressing the strong secondary flow, while with further increase of Reynolds number, the torque characteristics approach the zero magnetic field case, showing very weak effect of magnetic field.