Dynamics of turbulent natural convection in a cubic cavity with centrally placed partially heated inner obstacle

Natural convection in a cavity with a partially heated obstacle at the center at the Rayleigh number Ra=1.46×109 is investigated using large eddy simulation (LES). The standard and dynamic Smagorinsky models, as well as the wall-adapting local eddy-viscosity model, are used for the subgrid scales, and the flow statistics are compared with recent experiments. The LES results obtained with different meshes show overall good agreement with the experiments as concerns the flow and heat transfer. Simulation with a non-ideal wall at the adiabatic side of the obstacle is also performed to explain the residual discrepancies observed in the unheated channel. Additional simulations performed with periodic conditions in the spanwise direction are very different from the full three-dimensional (3D) simulations, which demonstrate the significance of 3D effects in the cavity. In particular, periodic simulations show Tollmien–Schlichting kind waves in the transitional region, while the 3D cavity shows an early cross-flow transition to turbulence.