Gas radiation effect on a turbulent thermal plume in a confined cavity using direct numerical simulation

Influence of gas radiation on a thermal plume is investigated in a cubical cavity filled with humid air (air/H₂O mixture) by means of Direct Numerical Simulation. In this work, radiation within the fluid is considered by the SLW model developed by Denison and Webb and numerically solved using the Discrete Ordinate Method (S₈ quadrature). The simulations are conducted for humid air with different amounts of water vapor and compared to the case without radiation. Two values of the Rayleigh numbers, $2\times {10}^6$ and 10⁹, are considered, corresponding to steady and turbulent flow regimes. Steady solutions show that gas radiation tends to reduce the spatial spreading of the thermal plume and to homogenize the temperature field away from the heat source. Gas radiation also results in an attenuation of the global circulation. It is shown that the radiative fluxes are much higher than convective fluxes on the isothermal walls, and the radiative heat transfer still increases with the water vapor concentration. For the turbulent regime, accounting for radiation leads to a less fluctuating behavior of the plume and induces a global shift of the mean temperature field in most of the cavity, except in the region around the heat source. Regarding the mean flow field, thermal radiation tends to weaken the intensity of flow circulation, but to accelerate the flow velocity along the centerline above the heat source.