Flow instability of natural convection in horizontal annuli under non-Oberbeck-Boussinesq condition

The hydrodynamic and thermal instabilities in the natural convection in horizontal concentric annuli have been studied extensively under the Oberbeck-Boussinesq (constant-property) assumption. However, the effects of the variable properties on the instabilities of these systems have not been fully understood. In this work, numerical simulations and theoretical analysis are performed to investigate the flow instability under non-Oberbeck-Boussineq conditions for a wide range of the temperature difference ratios and radius ratios. A variable-property-based lattice Boltzmann flux solver is used to account for the total variation in fluid properties. The results demonstrate that the variable property effect and the initial condition effect play important roles in determining the flow pattern, and that the significance of both effects depends strongly and non-monotonically on the temperature difference ratio.