In order to examine the characteristics of the various types of convection that can occur in a fluid-saturated porous material, numerical experiments are carried out for a permeable-top box heated from below. A cyclic reduction method is applied for solving Poisson-type pressure equation to avoid false flow fields due to the iterative numerical noise and a modified upwind scheme is utilized to overcome diffusional truncation errors in solving energy equation of parabolic type.
The main results of the present study are as follows. The conditions leading to onset of multicellular steady convections, second critical Rayleigh numbers above which fluctuating unsteady convections exist, variations of Nusselt number with Rayleigh number, and the effective convection patterns which maximize the heat transport are determined as functions of convective cell-number.
In summary, the results show that the various types of convection are possible for a given Rayleigh number and box geometry depending on the initial conditions.