Direct Numerical Simulation of Convective Turbulent Channel Flow of Fluid Mixtures

Fluid mixtures play an important role in a large variety of applications ranging from atmospheric flows to intracellular transport mechanisms. At the same time they present a significant challenge with regards to modeling and computational costs. In this work, the feasibility of treating a mixture of two fluids with different fluid properties by considering one species as the carrier fluid and treating the effect of an added trace species as a perturbative modification is explored. Towards this end, the concentration of the trace constituent is introduced as an active scalar within the flow and used as an expansion parameter analogously to the temperature in the Boussinesq approximation. For the example of a mixture of water vapor and dry air, the effects due to the added buoyancy are investigated using direct numerical simulations (DNS) of turbulent channel flow. The limitations concerning the validity of the strict Boussinesq approximation are determined, and an extended formulation is employed to explore higher order effects which become significant towards and outside of the limits of this range.