Direct numerical simulation of turbulent heat transfer in pipe flows: Effect of Prandtl number

Direct numerical simulations of heat transfer in a fully developed turbulent pipe flow with isoflux condition imposed at the wall are performed for a Reynolds number based on pipe radius Re = 5500. Main emphasis is placed on Prandtl number effects on turbulent heat transfer in pipe flow. The scaling of mean temperature profiles is investigated in order to derive correct logarithmic law for various Pr. The rms of temperature fluctuations and turbulent heat fluxes are found to increase when increasing Prandtl number. The turbulent Prandtl number, Pr, is almost independent of the molecular Prandtl number Pr for Pr >= 0.2. The radial distributions of higher order statistics (skewness and flatness) confirm the intermittent behaviour at the close vicinity of the wall; this intermittent behaviour is more pronounced with an increase in Pr. The Nusselt number is in good agreement with the findings of the literature. Probability density functions and joint probability density functions of velocity and temperature fluctuations are used to describe the characteristics of the turbulent flow and heat transfer. The instantaneous flow and thermal fields are plotted in order to analyse the turbulent structures. To explore the impact of the wall curvature on turbulent heat transfer, predictions were compared to available results for channel flow. These comparisons show a slightly more intense temperature fluctuations in the pipe flow. (c) 2007 Elsevier Inc. All rights reserved.