This report presents a study of numerical simulations of mixing layers developing between opposing flows of paired fluids under supercritical conditions, the purpose of the study being to elucidate chemical-species- specific aspects of turbulence. The simulations were performed for two different fluid pairs — O2/H2 and C7H16/N2 — at similar reduced initial pressures (reduced pressure is defined as pressure ÷ critical pressure). Thermodynamically, O2/H2 behaves more nearly like an ideal mixture and has greater solubility, relative to C7H16/N2, which departs strongly from ideality. Because of a specified smaller initial density stratification, the C7H16/N2 layers exhibited greater levels of growth, global molecular mixing, and turbulence. However, smaller density gradients at the transitional state for the O2/H2 system were interpreted as indicating that locally, this system exhibits enhanced mixing as a consequence of its greater solubility and closer approach to ideality. These thermodynamic features were shown to affect entropy dissipation, which was found to be larger for O2/H2 and concentrated in high-density-gradient-magnitude regions that are distortions of the initial density-stratification boundary. In C7H16/N2, the regions of largest dissipation were found to lie in high-density-gradient-magnitude regions that result from mixing of the two fluids.

This work was done by Josette Bellan, Kenneth Harstad, and Nora Okong'o of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at under the Physical Sciences category. NPO-30561.

This Brief includes a Technical Support Package (TSP).
Turbaulance in Supercritical O2/H2 and C7H16/N2 Mixing Layers

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This article first appeared in the April, 2003 issue of NASA Tech Briefs Magazine.

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