DNS of Heat Transfer in a Transitional Channel Flow Accompanied by a Turbulent Puff-like Structure

Abstract

-Direct numerical simulations of turbulent heat transfer in fully-developed channel flows have been performed in a range of friction Reynolds number between 60 and 180, based on the friction velocity and the channel half width δ, with emphasis on a puff-like structure, large-scale spatial intermittency. For the Reynolds numbers lower than 80 with a large computational domain of 51.2 × 2 × 22.5, the turbulent puff was observed and its significant influences on the momentum and heat transports were found. The spatial structure of the equilibrium puff, or the localized turbulence, was examined with taking account of two different thermal boundary conditions: the uniform heat-flux heating and the constant temperature difference between the walls. It was revealed that there existed a localized strong turbulent region in the form of an oblique band, along which a spanwise secondary flow was induced. In consequence, at the present lowest Reynolds number as low as 60, the flow remained turbulent and the larger Nusselt numbers than those without puff was obtained by the presence of puff.

Turbulent-laminar patterns in plane Poiseuille flow

“…19 In terms of wall units, our resolution is the same or finer than that used in these studies. Our resolution is also close to that used by Tsukahara et al 15,16 for Re = 1732 (Re τ = 80) and Re = 1327 (Re τ = 64) and higher than that of Brethouwer et al, 14 who used x + = 15, z + = 6.7, and N y = 32 for a case with Re = 700 (Re τ = 69). The timestep varied from t = 0.03 for Re = 900 to t = 0.015 for Re = 2300.…”

“…[6][7][8][9][10][11][12][13][14] Turbulent-laminar banded patterns have also been observed numerically and experimentally in plane Poiseuille (channel) flow. [14][15][16][17][18] Tsukahara et al 16 presented detailed visualizations from numerical simualtions of the mean flow as well as the effect of turbulent bands on heat transport. Later experiments 18 compared the range of Reynolds numbers, wavelengths, and angles of the turbulent bands obtained experimentally with the numerical results reported by Tsukahara et al 17 Brethouwer et al…”

“…One standard choice, and that made here, is to impose the bulk velocity and to scale the velocity by 3u bulk /2, because this leads to Re b = Re c for the laminar flow. Many of the references we cite use another factor, one 14 or two, [15][16][17][18][19] in place of the 3/2; when we cite Reynolds numbers from these references, we have multiplied them by the appropriate conversion factor of 3/2 or 3/4. Unless mentioned otherwise, the Reynolds number Re b is denoted merely by Re.…”

“…All of the references cited previously [14][15][16][17][18] reported patterns with wavelengths in the range [20,30]. In our domain, only patterns whose wavelength is a divisor of L z can be simulated, i.e., 40, 20, 10, etc.…”

Turbulent Heat Transfer in Drag-Reducing Channel Flow of Viscoelastic Fluid

“…Note that we applied the coefficient 0.020, which was recommended by Tsukahara et al (2006), in place of 0.022 originally given by Kays & Crawford (1980); however, we used 0.025 for Pr = 0.1 to ensure a consistency with the Newtonian case. For a unit value of Prandtl number (Pr = 1.0), the obtained HTR%i sa tt h es a m eo r d e ro f magnitude as DR% in each case (see Table 3).…”