# Lattice Boltzmann simulations of three-dimensional thermal convective flows at high Rayleigh number

## TL;DR

This paper demonstrates the use of thermal lattice Boltzmann simulations to analyze three-dimensional high Rayleigh number convective flows, providing results consistent with benchmark data for both laminar and turbulent regimes.

## Contribution

The study introduces a thermal LB model with double distribution functions for simulating high Rayleigh number convection, achieving isotropy and validating results against benchmarks.

## Key findings

- Steady hydrodynamic and Nusselt numbers at Ra=10^6 and 10^7 in side-heated cells.
- Statistical averages of Reynolds and Nusselt numbers in Rayleigh-Bénard convection.
- Consistent results with existing benchmark data.

## Abstract

We present numerical simulations of three-dimensional thermal convective flows in a cubic cell at high Rayleigh number using thermal lattice Boltzmann (LB) method. The thermal LB model is based on double distribution function approach, which consists of a D3Q19 model for the Navier-Stokes equations to simulate fluid flows and a D3Q7 model for the convection-diffusion equation to simulate heat transfer. Relaxation parameters are adjusted to achieve the isotropy of the fourth-order error term in the thermal LB model. Two types of thermal convective flows are considered: one is laminar thermal convection in side-heated convection cell, which is heated from one vertical side and cooled from the other vertical side; while the other is turbulent thermal convection in Rayleigh-B\'enard convection cell, which is heated from the bottom and cooled from the top. In side-heated convection cell, steady results of hydrodynamic quantities and Nusselt numbers are presented at Rayleigh numbers of $10^6$ and $10^7$, and Prandtl number of 0.71, where the mesh sizes are up to $257^3$; in Rayleigh-B\'enard convection cell, statistical averaged results of Reynolds and Nusselt numbers, as well as kinetic and thermal energy dissipation rates are presented at Rayleigh numbers of $10^6$, $3\times 10^6$, and $10^7$, and Prandtl numbers of 0.7 and 7, where the nodes within thermal boundary layer are around 8. Compared with existing benchmark data obtained by other methods, the present LB model can give consistent results.