Flow state transition and heat transfer characteristics in radiative Rayleigh–Bénard convection

The Rayleigh–Bénard (RB) convection under the influence of thermal radiation holds paramount importance in both natural systems and engineering applications, like advanced energy storage systems, renewable energy conversion technologies, and high-efficiency power generation systems, etc. Remarkably, thermal radiation significantly modifies flow dynamics and heat transport in RB convection. In this paper, direct numerical simulations of two-dimensional radiative RB convection in a square cavity have been conducted within the range of Rayleigh number Ra = 5 × 105–5 × 109, Planck number Pl = 0.005–0.16, and optical thickness τ = 0.01–50. By incorporating radiative heat transfer mechanisms into the classical buoyancy-driven convection framework, we elucidate the coupled effects of thermal radiation and fluid motion on heat transport efficiency and flow structure evolution. The simulation results reveal that thermal radiation imposes a stabilizing effect on the flow state of RB convection, promoting the transition from disordered chaotic flow to organized steady-state circulation. The impact of thermal radiation on convective heat transfer is complex and can be stratified into three distinct regimes, i.e., radiation-sensitive regime, transition regime, and buoyancy-dominated regime. The evolution of flow structures influenced by thermal radiation varies distinctly across different regimes, thereby exerting a profound influence on convective heat transfer. Conversely, the radiative and total heat transfer always decrease continuously with the attenuation of thermal radiation. These findings advance understanding of radiation-convection coupling in complex systems.