Abstract
A study is made of the unsteady hydromagnetic boundary layer flow induced by the torsional oscillations of an infinite disk in an electrically conducting rotating fluid in the presence of a uniform magnetic field. Information is obtained about: (i) the structure of the steady and the unsteady flow field; (ii) the development of the Stokes-Ekman-Hartmann boundary layers with their physical implications; (iii) the significant interaction of the electromagnetic and Coriolis forces; (iv) the hydromagnetic Ekman suction velocity and total transient time required for the establishment of the hydromagnetic boundary layers; and (v) the generation and propagation of a series of inertial oscillations and the diffused hydromagnetic waves. It is shown that the rapid attainment of the Stokes-Ekman-Hartmann boundary layers and the striking properties of the Ekman suction velocity play a distinctive role on the hydromagnetic spin-up process.