DNS study of turbulent transport at low Prandtl numbers in a channel flow

Abstract

Direct numerical simulations of the velocity and temperature fields for turbulent flow in a channel are used to examine the influence of Prandtl number Pr on turbulent transport. The Reynolds number, based on the half-height of the channel and the friction velocity, is Reτ = 150. Prandtl numbers of 1.0, 0.3, 0.1, 0.05, 0.025 were studied. The bottom and the top walls were kept at constant temperatures of +Tw and −Tw. The influence of Pr on Reynolds transport, on the turbulent diffusivity, ατ, and on the spectral density function of the temperature fluctuations was studied. The observation that spatial variations of the ratio of the turbulent diffusivity to the value observed at Pr = 1.0 are not large is used to propose a method for calculating average temperature fields. The decrease in ατ with decreasing Pr is related to observations of the increased damping of high-wavenumber temperature fluctuations. Molecular conductivity, at smaller Pr, is pictured to act as a filter that renders high-frequency velocity fluctuations ineffective in transporting heat.

Turbulence and transport of passive scalar in magnetohydrodynamic channel flows with different orientations of magnetic field

“…6 is qualitatively similar to the transformation observed in the hydrodynamic case at decreasing Pr (Piller et al, 2002;Na et al, 1999). Both the transformations are caused by suppression of the wall-normal turbulent transport of the scalar.…”

“…The numerical model has been verified by running test cases and comparing the results with MHD flow computations (Lee and Choi, 2001;Boeck et al, 2007;Krasnov et al, 2008) and DNS of scalar transfer in turbulent channel flows without and with magnetic field (Piller et al, 2002;Yamamoto et al, 2008).…”

Effect of magnetic field on near-wall coherent structures and heat transfer in magnetohydrodynamic turbulent channel flow of low Prandtl number fluids

“…doi:10.1016/j.ijheatmasstransfer.2011.03.026 heat flux have been investigated in several numerical studies [13][14][15][16][17][18][19]. In contrast to the hydrodynamic flow, it seems that there are only few attempts to explore numerically the heat transfer in turbulent channel flows in the presence of magnetic fields.…”

Direct numerical simulation of turbulent forced convection in a pipe

“…The results by Kong et al [4] for a turbulent thermal boundary layer, with both iso ux and isothermal boundary conditions, agree with the observations by Tiselj et al [3], in that the in uence of the temperature boundary conditions is conÿned to the range y + ¡10. Piller et al [5] carried out several DNS for the channel ow with the two walls kept at constant, di erent temperatures, for Re * h = 150 at Pr = 0:025; 0:05; 0:1; 0:3 and 1.0. More recently, Seki et al [6] compared the turbulence temperature statistics for channel ows at two Reynolds numbers, with two di erent boundary conditions: constant temperature di erence between top and bottom surfaces and MT conditions.…”