Numerical and experimental study of the influence of a cylindrical obstacle on the heat transfer in a differentially heated cavity*

Heat transfer enhancement in free convection systems is a challenge for many industrial processes, such as nuclear reactors cooling, electronic circuits or building's ventilation. The rectangular differentially heated cavities (DHC) are the best model to study it. The key factor to succeed in is to destabilize the laminar thermal boundary layers in order to enhance the temperature gradient at the walls. In this work, we numerically study the influence of a conductor or not conductor cylinder located at the bottom of the hot plate, perpendicular to it, in a DHC of aspect ratio 4. Various Rayleigh numbers (or temperature difference) are considered. When the cylinder is not conductor we perturb the velocity fields first and in a second step, the temperature fields. When it is conductor we perturb both fields by both mechanisms, thermal and mechanical. The cavity, filled with air (Prandtl number = 0.71). Direct numerical simulations of the three-dimensional incompressible Navier-Stokes-Boussinesq equations, are performed using the spectral element method with a P_n-P_n-2 formulation, with polynomial order 7, written in the open source code Nek5000. The results are contrasted with experimental data and we show the effect of a cylinder on the heat transfer.