Simulation of regimes of convection and plume dynamics by the thermal Lattice Boltzmann Method

Abstract

We present 2D simulations using the Lattice Boltzmann Method (LBM) of a fluid in a rectangular box being heated from below, and cooled from above. We observe plumes, hot narrow upwellings from the base, and down-going cold chutes from the top. We have varied both the Rayleigh numbers and the Prandtl numbers respectively from Ra=1000 to Ra=1010 , and Pr=1 through Pr=5×104, leading to Rayleigh-Bénard convection cells at low Rayleigh numbers through to vigorous convection and unstable plumes with pronounced vortices and eddies at high Rayleigh numbers. We conduct simulations with high Prandtl numbers up to Pr=50,000 to simulate in the inertial regime. We find for cases when Pr⩾100 that we obtain a series of narrow plumes of upwelling fluid with mushroom heads and chutes of downwelling fluid. We also present simulations at a Prandtl number of 0.7 for Rayleigh numbers varying from Ra=104 through Ra=107.5. We demonstrate that the Nusselt number follows power law scaling of form Nu∼Raγ where γ=0.279±0.002, which is consistent with published results of γ=0.281 in the literature. These results show that the LBM is capable of reproducing results obtained with classical macroscopic methods such as spectral methods, and demonstrate the great potential of the LBM for studying thermal convection and plume dynamics relevant to geodynamics.