VARIABLE POROSITY AND THERMAL DISPERSION EFFECTS ON VORTEX INSTABILITY OF A HORIZONTAL NATURAL-CONVECTION FLOW IN A SATURATED POROUS-MEDIUM

A numerical analysis is made to analyze the variable porosity and ther mal dispersion effects on the vortex mode of instability of a horizont al natural convection boundary layer flow in a saturated porous medium . The porosity of the medium is assumed to vary exponentially with dis tance from the wall. In the base flow, the governing equations are sol ved by using a suitable variable transformation and employing an impli cit finite difference Keller Box method. The stability analysis is bas ed on the linear stability theory and the resulting eigenvalue problem is solved by the local similarity approximations. The results indicat e that both effects increase the heat transfer rate. In addition, the thermal dispersion effect stabilizes the flow to the vortex mode of di sturbance, while the variable porosity effect destabilizes it.