Influence of air region size on the onset of thermal convection in an “air–heat-generating porous medium–air” system

Abstract

The problem concerning convective stability of the motionless air state in a layered air–heat-generating porous medium–air system under the gravitational field is simulated numerically in the paper. We take into consideration the heat source strength dependent on solid volume fraction in the porous sublayer. Marginal stability curves are presented at different values of the relative depth of the air sublayer. It has been shown that the onset value of internal convection decreases with increasing this depth. Besides, the convective roller flow is of a large-scale character at low relative depths, but it can be localized within the upper air sublayer at high enough depths. A comparison of the threshold internal Rayleigh-Darcy numbers at equal ratios of the air to porous depths has shown that the enhancement of convection (or lowering its threshold) is more effective in the three-layered air–heat-generating porous medium–air system as compared to that of the two-layered air–heat-generating porous medium system.