Heating intensity and radiative effects on turbulent buoyancy-driven airflow in open square cavities with a heated immersed body

The influence of the radiative heat transfer and the effects of air variable properties on the natural convection flows within a vented square cavity with a heated inner body are numerically investigated. Two-dimensional, unsteady, laminar, transitional and turbulent simulations are obtained, for both uniform wall temperature and uniform heat flux heating conditions. The average Nusselt number and the dimensionless mass-flow rate are obtained for a wide range of the Rayleigh number varying from 104 to 1012. The results obtained for different heating intensities are analyzed and compared. The influence of considering surface radiative effects on the differences reached for the Nusselt number and the mass-flow rate obtained with several heating intensities is studied for the isothermal heating condition. For isoflux heating, the obtained results show that the effects of thermal radiation on the appearance of the burnout phenomenon are particularly relevant under given circumstances. The conditions under which the flow becomes unstable, giving rise to a transient, mainly oscillating solution, are determined. The relevant changes produced in the flow patterns into the cavity, are also explained.