The present paper is devoted to the study of the magnetohydrodynamic (MHD) flow of an incompressible viscous and electrically conducting fluid due to an infinite porous rotating disk at small distance from a porous medium. A uniform suction is applied through the surface of the disk. The domain of flow is divided into two regions: the free fluid region between the disk and the porous medium and the porous region. The governing equations of motion, in terms of cylindrical polar coordinates, are reduced to a set of nonlinear ordinary differential equations by similarity transformations and then solved by using the approximation method. The solutions are obtained by solving Navier-Stokes equations in the free fluid region, and Brinkman equations in the porous region with adequate boundary conditions at the interface. Graphical representation of the results are outlined for different values of Hartmann number, suction parameter and the porosity of the medium. The effect of these parameters upon the velocity fields are examined. The torque acted on the disk have been also computed. The main result of the present work is that, the presence of the magnetic field effects on the velocity field in both flow regions. This effect depends on the suction process. It is also noticed that the magnetic field reduces the velocity components, while suction process increases them. Therefore, the torque due to viscous friction acting on the disk increases with increasing the magnetic field strength. |
