Large-eddy simulations of turbulent heat transfer in stationary and rotating square ducts

Abstract

Turbulent heat transfer at low Reynolds numbers in stationary and rotating straight square ducts was simulated using the large-eddy simulation technique. For the rotating square duct flows, the rotation axis was parallel to two opposite walls of the duct. The pressure-driven flow was assumed to be hydrodynamically and thermally fully developed. A constant and uniform heat flux distribution in the axial direction was applied at the four smooth walls of the forced and mixed convection flows. Two boundary conditions for the thermal energy equation were examined: constant peripheral wall temperature and uniform peripheral wall heat flux. Computations were carried out using a second-order finite volume code with a localized one-equation dynamic subgrid scale model. For the simulated nonrotating flows, there were significant differences of about 16% in the overall Nusselt numbers, depending on the type of thermal boundary condition applied at the walls. This was because of the presence of the corners. Simulations of mixed convection arising from the centrifugal buoyancy effect showed that the turbulence level of the flow was strongly influenced by the centrifugal buoyancy effect. At the rotation rate considered, the overall Nusselt numbers and the turbulence levels of the flow were not greatly affected by the type of boundary conditions for temperature applied at the walls. However, temperature fluctuation intensities noticeably increased when a uniform peripheral heat flux was imposed at the walls.