The turbulent Prandtl number in the near-wall region for low-Prandtl-number gas mixtures

Abstract

Results of experiments for binary gas mixtures, with molecular Prandtl numbers in the range 0.18–0.7 in flow in a smooth circular tube with constant transport properties were employed to examine models hypothesized for the distribution of the turbulent Prandtl number, Pr t,{{ y +, Pr, Re}}. These models included approximations of predictions from recent direct numerical simulations of turbulent duct flows. Data for a range of molecular Prandtl numbers for ‘high“ Reynolds numbers, ≈ 3 × 10 4 < Re < ≈ 1 × 10 5, were obtained earlier by the authors by utilizing mixtures formed by helium or hydrogen with xenon, argon or carbon dioxide. For the range 0.21 < Pr < 0.72, Reynolds analogy and the variable Pr t{{ y +, Pr, Re}} model by Kays agreed with downstream measurements to within about 5%.