Effect of viscosity, capillarity and grid spacing on thermal variable-density flow

SummaryThe HydroGeoSphere model is further developed and used to investigate the effects of viscosity, capillarity and grid spacing on thermal variable-density flow. Under saturated and unsaturated flow conditions, the flow dynamics significantly depends on the viscosity assumption (constant vs. variable), where downwelling regions (constant viscosity) become upwelling regions (temperature-dependent variable viscosity). Capillarity does not change the location of downwelling and upwelling regions. Capillarity can significantly alter the flow dynamics in the way that the water table acts as a “lid” to flow, and it diverts a thermal plume laterally. Significance of capillarity increases with increasing soil moisture. Thermal convective flow is highly sensitive to spatial discretization. While the flow dynamics remains to be a function of grid level, spatial discretization Δx = Δz = 1 m appears to be appropriate to simulate unsaturated variable-density flow and heat transfer in porous media because estimated errors have asymptotically reached a minimum.

Research highlights► Effect of viscosity, capillarity and grid spacing on thermal variable-density flow. ► Flow dynamics significantly depends on the viscosity assumption (constant vs. variable). ► The water table diverts a thermal plume laterally. ► Thermal variable-density flow is highly sensitive to spatial discretization.