The influence of near-wall density and viscosity gradients on turbulence in channel flows

摘要: The influence of near-wall density and viscosity gradients on turbulence in a channel are studied by means Direct Numerical Simulation (DNS) the low-Mach number approximation Navier--Stokes equations. Different constitutive relations for as function temperature used order to mimic wide range fluid behaviours develop generalised framework studying modulations variable property flows. Instead scaling velocity solely based local density, done van Driest transformation, we derive an extension that is semi-local Reynolds $Re_\tau^*$. This transformation able collapse profiles flows with wall coordinate. However, flow quantities like mixing length, anisotropy turbulent vorticity fluctuations do not show universal very close wall. attributed modulations, which play crucial role evolution structures energy transfer. We therefore investigate characteristics streamwise streaks quasi-streamwise vortices found that, similar statistics, also strongly governed $Re_\tau^*$ their dependence individual minor. Flows ($d {Re_\tau^*}/dy \neq 0$) showed significant changes inclination tilting angles vortices. These structural responsible observed modulation stress generation mechanism inter-component transfer strong gradients.