Effects of Heat Loss and Gas Radiation on Turbulent Natural Convection in an Enclosure

The natural convection flow of air within a differentially heated cubic cavity (DHCC) has received considerable attention as a benchmark problem, owing to its relevance across various applications such as natural convection in solar chimneys or the natural ventilation of buildings. In this study, the Large Eddy Simulation (LES) technique was employed to scrutinize turbulent natural convection of both humid and dry air within a DHCC at a Rayleigh number of 1.58×10 ⁹ . The choice of the WALE sub-grid scale model over the Dynamic Smagorinsky-Lilly model stems from turbulence modelling results, indicating it necessitates up to 11% fewer computational resources. This is particularly noteworthy considering the inherently time-consuming nature of LES computations. After turbulence modelling, the role of small contents of water vapor in the thermal-fluid characteristics of the buoyant flow has been appraised. It was observed that the radiative properties of water vapor affect the flow features. It intensifies the buoyancy, and especially near the hot wall, increases the velocity peak and boundary layer thickness, but decreases the turbulent activities near the cold wall. Finally, the role of boundary conditions applied on the horizontal passive walls is explored. The LES results suggest that the type of boundary condition has noticeable impacts on the mean flow features and turbulence statistics with pronounced effects in the near-wall region. Applying highly conducting walls causes heat exchanges with the external ambient which in turn intensifies the buoyancy effects, increases turbulent activities, and brings unsteadiness to the flow downstream of the passive walls. The present findings indicate that precise modelling of both the BCs and air humidity is required to accurately assess fluid flow and heat transfer, and turbulent statistics, for natural convection flows in enclosed cavities.