Turbulent forced convective flow in an anisothermal channel

• LES of turbulent channel flow is performed with anisotropic temperature-dependent viscosity.
• A systematic analysis of variable-viscosity effects, isolated from gravity is carried out.
• Turbulence is enhanced in the cold side of the channel while suppressed at hot wall.
• Turbulent structures near cold wall are short and densely populated while fewer at hot wall.
• Spectral study reveals that turbulence is completely suppressed at the hot side of channel.

The influence of variable viscosity effects on momentum and heat transfer of a non-isothermal turbulent forced convective flow is studied using thermal large-eddy simulation (LES). LES of bi-periodic channel flow with significant heat transfer at a low Mach number was performed to study the modulation in the near-wall turbulence structure due to anisotropic viscosity. The temperature ratio (Rθ = Thot/Tcold) is varied from 1.01 to 5 to study the isolated effect of variable viscosity with (Thot) and (Tcold) as a wall temperature. It is shown that average and turbulent fields undergo significant changes in a broad range of Reynolds number, compared to isothermal flow with constant viscosity, we observe enhanced turbulence on the cold side of the channel, characterized by locally lower viscosity whereas a decrease of turbulent kinetic energy is found at the hot wall. The turbulent structures via H criteria of high vorticity shows very short and densely populated vortices near cold wall whereas long streaky structure or large elongated vortices at the hot wall. Q invariant totally eradicate all the streaky structure at the hot wall as a consequence of relaminarization. To further clarify this issue spectral study is conducted that reveals complete suppression of turbulence at the hot side of the channel at large temperature ratio because no inertial zone (i.e. index of Kolmogorov scaling law is zero) is obtained on the spectra in these region.