Influence of turbulent natural convection on heat transfer in shallow caves

We aim at analyzing in detail the different heat transfer mechanisms involved in a confined shallow cave embedded in a rock massif submitted to seasonal variations of the ground temperature. Heat conduction in the rock massif, radiative heat transfer between cave walls, and turbulent natural convection inside the cave are considered. The natural convection problem is solved by large-eddy simulations (LES) using a Chebyshev pseudo-spectral method associated with a spectral vanishing viscosity (SVV) model. The thermal boundary conditions applied to the cave walls are obtained from a large-scale model that takes into account heat conduction in the rock massif and radiative fluxes between cave walls. This approach allows us to characterize the relative strength of convective and radiative fluxes and to identify the regions of the cavity and times of the year of intense heat transfer. We identified two different flow regimes: (i) a one-cell flow regime associated with strong convection, high turbulence level and unstable mean vertical temperature gradient, (ii) a multiple cell flow regime associated with weak convection, low turbulence level and stable mean vertical temperature gradient. The use of the Newton's law to describe convection heat fluxes at the cavity walls is discussed.