This report describes a study of databases produced by direct numerical simulation of mixing layers developing between opposing flows of two fluids under supercritical conditions, the purpose of the study being to elucidate chemical species-specific aspects of turbulence, with emphasis on helicity. The simulations were performed for two different fluid pairs — O2/H2 and C7H16/N2 — at similar values of reduced pressure.
This work was done by Nora Okong'o and Josette Bellan of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package free on-line at www.techbriefs.com/tsp under the Physical Sciences category.
NPO-30894
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Helicity in Supercritical O2/H2 and C7H16/N2 Mixing Layers
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Overview
The document titled "Helicity in Supercritical O₂/H₂ and C₇H₁₆/N₂ Mixing Layers" presents research conducted by Nora Okong’o and Josette Bellan at the Jet Propulsion Laboratory, focusing on the dynamics of supercritical mixing layers. The study investigates the behavior of these layers under varying initial conditions, particularly emphasizing the differences between oxygen/hydrogen (O₂/H₂) and heptane/nitrogen (C₇H₁₆/N₂) systems.
The research is motivated by the need to understand mixing layers in supercritical conditions, which are relevant to applications in liquid rocket engines (O₂/H₂) and gas turbine/diesel engines (C₇H₁₆/N₂). The document outlines the methodology used for Direct Numerical Simulations (DNS) of these mixing layers, which are characterized by strong density stratification between the two free streams. The authors highlight the importance of coherent structures in the evolution of these layers and how they are perturbed to study their dynamics.
Key findings include the observation that the O₂/H₂ layers, due to their higher initial density stratification, do not reach a transitional state under certain conditions (Re₀ = 600), making direct comparisons with the C₇H₁₆/N₂ system challenging. The document details several meaningful comparisons between different layers, focusing on their Reynolds numbers and initial conditions, such as density ratios and temperature.
The authors also discuss the implications of thermodynamic properties on the helicity characteristics of the mixing layers, which is crucial for understanding the mixing and combustion processes in supercritical environments. The results contribute to a deeper understanding of the fundamental physics governing these systems, which can inform the design and optimization of engines and other applications where supercritical fluids are utilized.
In conclusion, the document serves as a comprehensive resource for researchers and engineers interested in the dynamics of supercritical mixing layers, providing insights into the complexities of fluid behavior under varying thermodynamic conditions. It emphasizes the need for further investigations to bridge the knowledge gap between different species systems and their respective applications in aerospace technology.
