Stable Stratification in Wall-Bounded Turbulent Flows

Abstract

Direct Numerical Simulation (DNS) is used to study the behavior of stably-stratified turbulent channel flow with temperature-dependent fluid properties: specifically, viscosity (μ) and thermal expansion coefficient (β). The governing equations are solved using a pseudo-spectral method for the case of turbulent water flow in a channel at Re τ = 150 and Gr ≃ 107. After an initial transient evolution of the flow, a statistically-stationary condition occurs, in which active turbulence and Internal Gravity Waves (IGW) coexist. In this condition, the transport efficiency of momentum and heat reduces considerably with respect to the condition of non-stratified turbulence. The crucial role of temperature-dependent viscosity and thermal expansion coefficient is directly demonstrated. The most striking feature produced by the temperature-dependent of viscosity is flow relaminarization in the cold side of the channel (where viscosity is higher). The opposite behavior, with flow relaminarization occurring in the hot side of the channel, is observed when a temperature-dependent thermal expansion coefficient is considered.KeywordsLarge Eddy SimulationDirect Numerical SimulationInternal WaveThermophysical PropertyCold SideThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.