MHD stagnation-point flow.

Abstract

The flow near a stagnation-point is a fundamental topic in fluid dynamics and it has been studied by several researches during the past decades because of its relevant applications. In this Thesis we investigate the influence of the electromagnetic field on the stagnation-point flow of a Newtonian or a micropolar fluid. To this end we consider three types of such a motion: plane orthogonal, plane oblique and three-dimensional. We take into consideration a fluid which moves towards a flat surface. We descrive several situations which are relevant from a physical point of view when an external uniform or not uniform electromagnetic field is impressed. Actually, we have prove that if the external magnetic field is uniform and the induced magnetic field is neglected, then the stagnation-point flow exists if, and only, if the external magnetic field has some suitable directions. Further, we compute the induced magnetic field in the other cases. We prove also that if the external magnetic field is not uniform and it is parallel to the velocity at infinity then the three-dimensional stagnation-point flow is possible if and only if it is axisymmetric. In all the cases here considered, the MHD PDEs which govern the motion are reduced to a system of nonlinear ODEs. These boundary values problems are then integrated numerically and some graphics and tables are furnished in order to show the behaviour of the solution near the obstacle.