MHD FLOW AND HEAT-TRANSFER AT A GENERAL 3-DIMENSIONAL STAGNATION POINT

The flow characteristics of an incompressible viscous electrically con ducting fluid at a three-dimensional stagnation point with arbitary ve locity gradients a and b (with a>0 and \b\ less than or equal to a) in two orthogonal directions are determined. A similarity solution of th e boundary layer equations for this flow over a surface permeated by a uniform transverse magnetic field is obtained when the surface is sub jected to injection. Two types of stagnation point flows are distingui shed: (i) nodal point how when 0 < alpha less than or equal to 1 with alpha = b/a and (ii) saddle point flow with -1 < alpha < 0. It is foun d that for nodal point dow the Velocity component v in the boundary la yer in the direction of the free stream with velocity gradient b appro aches the free stream velocity more slowly than the corresponding velo city component u along the free stream with velocity gradient a. Furth er velocity at a point in the boundary layer increases with increase i n the magnetic parameter M. It is found that at a saddle point for M = 0, a back how in the v-profile occurs at alpha = - 0.43. A novel resu lt of the analysis is that with increase in M, the magnitude of alpha for which the back flow in the v-profile first occurs also increases a nd for M = 1.258, no back flow occurs at all. Skin-friction components near nodal or saddle points corresponding to the u and v profiles are computed for Various Values of injection and magnetic parameters. Fin ally it is shown that increase in blowing results in decrease in the s urface heat transfer thus illustrating the salutary effect of blowing in cooling the surface. (C) 1997 Elsevier Science Ltd.