Pressure Effects from Direct Numerical Simulation of High-Pressure Multispecies Mixing

Abstract

The focus of this study is the understanding of effects of pressure increase or Reynolds number increase in supercritical-pressure flows. To this effect, Direct Numerical Simulations are conducted for supercritical-pressure flows in which five species undergo mixing. The computation of multispecies mixing is based on a full mass-diffusion matrix, a full thermal-diffusion-factor matrix necessary to include Soret and Dufour effects, and both viscosity and thermal conductivity computed for the species mixture. The scaling of the physical viscosity, necessary for conducting DNS, induces a scaling of the other transport properties that respects the accurate values of the Schmidt (Sc) numbers and of the Prandtl (Pr) number. Computations are performed in the configuration of a temporal mixing layer and the results are analyzed to reveal the separate effect of pressure or Reynolds number increase on the flow. The analysis consists of examining vortical aspects of the flow, the fluxes and relevant thermodynamic properties. It is found that a larger pressure has an opposite effect to a larger Reynolds number, mainly by increasing the fluid density and making it more difficult to entrain and mix.

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