Simplified and highly stable thermal Lattice Boltzmann method simulation of hybrid nanofluid thermal convection at high Rayleigh numbers.

A new method called simplified and highly stable thermal lattice Boltzmann method, which is based on the lattice Boltzmann framework, was used to simulate the hybrid nanofluid natural convection and heat transfer in a square enclosure with a heating obstacle at high Rayleigh numbers. Four fins protrude from the heating obstacle to affect the flow pattern and heat transfer performance. The effects of the Rayleigh number (106 ≤ Ra ≤ 109), nanoparticle volume fraction (0 ≤ ϕ ≤ 0.05), and length of the fin (0.1 ≤ h ≤ 0.3) on the flow pattern, temperature distribution, and heat transfer characteristics were illustrated and analyzed. To validate the present method, the benchmark simulation results were performed. Three kinds of flow patterns (steady symmetry, unsteady symmetry, and unsteady asymmetry) can be identified at various Rayleigh numbers. At different lengths of fins, the critical Rayleigh number of flow pattern transition (from steady symmetry to steady asymmetry and from steady asymmetry to unsteady asymmetry) is different. ϕ and h also significantly affect the flow pattern. At higher ϕ, the flow inside the enclosure is steadier and the effect of h on the flow pattern varies at different Ra. [ABSTRACT FROM AUTHOR]