Quasi-DNS of natural convection flow in a cylindrical annuli with an optimal polyhedral mesh refinement

A direct numerical simulation was used to study the buoyancy driven turbulent flow inside a horizontal annular cavity at Rayleigh number, Ra = 1.18 × 109, and cylinders diameters ratio of 4.85. Mean and rms temperature profiles are in good agreement with experiments. Turbulent kinetic energy budgets have been calculated to verify the accuracy of the unstructured finite volume code on polyhedral cells in Direct Numerical Simulation (DNS) mode. The code is found to return satisfactory results for first and second order statistics, and coherent turbulent kinetic energy budgets, except for the profile of the turbulence dissipation rate which may be underestimated due to 1% blended upwinding. The unstructured mesh was optimized using Kolmogorov scaling estimated by a precursor RANS simulation of this very inhomogeneous flow and two point correlations demonstrated that the domain size was sufficiently large.