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 www.techbriefs.com/tsp 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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Overview
The document is a technical support package prepared under the sponsorship of NASA, focusing on turbulence in supercritical mixing layers, specifically involving oxygen/hydrogen (O₂/H₂) and heptane/nitrogen (C₇H₁₆/N₂) systems. The work is attributed to inventors Josette Bellan, Kenneth G. Harstad, and Nora Okong'o from the Jet Propulsion Laboratory (JPL) at the California Institute of Technology.
The primary objective of the research is to model supercritical turbulence and understand the chemical-species-specific aspects of turbulence under these conditions. The study employs Direct Numerical Simulations (DNS) to resolve all scales of flow in the two species systems, allowing for a detailed analysis of turbulence characteristics.
Key findings indicate that turbulence dissipation, which is a measure of turbulence activity, is concentrated in regions of high density-gradient magnitude (HDGM). For the O₂/H₂ system, the largest dissipation occurs in areas where the original boundary between the two fluids is distorted. In contrast, for the C₇H₁₆/N₂ system, most dissipation activity is found in HDGM regions that arise from the mixing of the two fluids. This difference is attributed to the greater solubility and improved molecular mixing in the O₂/H₂ system compared to the C₇H₁₆/N₂ system.
The document emphasizes the importance of understanding these turbulence dynamics for applications in rocket propulsion, gas turbines, and diesel engines, where supercritical fluids are often encountered. The research contributes to the broader field of fluid dynamics by providing insights into how different fluid pairs behave under supercritical conditions, which is crucial for optimizing performance in various engineering applications.
The document also includes references to previous studies and methodologies that support the findings, highlighting the collaborative nature of the research and its grounding in established scientific literature. Overall, this technical report serves as a valuable resource for researchers and engineers interested in the complexities of supercritical fluid behavior and turbulence modeling.
