UNSTEADY HYDROMAGNETIC NATURAL CONVECTION OF A SHORT-MEMORY VISCOELASTIC FLUID IN A NON-DARCIAN REGIME: NETWORK SIMULATION

Abstract

A mathematical model for the unsteady magnetohydrodynamic (MHD) laminar natural convection flow of a viscoelastic fluid from an infinite vertical porous plate to an isotropic, homogeneous, non-Darcian porous regime, with time-dependent suction, in the presence of a uniform transverse magnetic field, is studied. The generalized Beard-Walters rheological model is employed, which introduces a mixed third-order derivative into the momentum conservation equation. The transformed conservation equations are solved using the robust, well-tested computational procedure known as network simulation method (NSM). The NSM computations have shown that with an increase in viscoelasticity parameter (S) the flow accelerates considerably with time. Increasing magnetic field (M), however, retards the flow strongly with time. An increase in the Darcy number (Da) serves to augment the velocity (w) profiles, i.e., accelerate the flow in both the conducting (M ≠ 0) and nonconducting (M = 0) cases. Velocities also increase in value over time (τ). A velocity overshoot is identified close to the plate. A rise in the Forchheimer number (Fs), corresponding to an accentuation in the quadratic porous drag effect, induces a strong deceleration in the flow, in particular near the plate surface, for both conducting and nonconducting cases. Increasing buoyancy effects, as simulated via a rise in the thermal Grashof number (Gr), leads to a substantial retardation in the flow; this effect is enhanced with Lorentzian magnetic drag force. An increase in the suction parameter (A) causes a stronger adherence of the hydrodynamic boundary layer to the plate and leads to a reduction in velocities along the entire plate regime. A similar decrease in temperature (θ) is caused with increasing suction parameter (A). The results are of relevance in, for example, magneto-rheological materials processing operations and advanced hybrid magnetohydrodynamic energy systems exploiting non-Newtonian fluids.