Large eddy simulations of a buoyant plume above a heated horizontal cylinder at intermediate Rayleigh numbers

Abstract

Large eddy simulations of a buoyant plume forming above a heated horizontal cylinder with a Rayleigh number of 9.4E7 is carried out and compared with experimental data. Natural convection heat transfer from a horizontal cylinder at this intermediate Rayleigh number involve a laminar to turbulent transition downstream the cylinder. A laminar to turbulent transition will alter the flow characteristic downstream cylinder considerably, thus it is important that the transition is captured in the simulations. Subgrid stresses are accounted for using the dynamic Smagorinsky model which allow for both laminar and turbulent flow through the dynamic procedure. The results show a considerable difference between the numerical and experimental results. Plume center vertical velocity is highly overpredicted compared to the experimental data. The computed half-width about 1.5 y/D downstream the cylinder is comparable to the experimental data, however, 3.5 y/D downstream cylinder, the half-width is only about half that of the experimental data. The half-width growth rate measured in the experiments remain higher than the computed growth rate throughout the domain of interest.