This report discusses direct numerical simulations (DNS) of a mixing layer between supercritical flows of oxygen and hydrogen. The governing conservation equations were those of fluctuation- dissipation (FD) theory, in which low-pressure typical transport properties (viscosity, diffusivity and thermal conductivity), are complemented, at high pressure, by a thermal-diffusion factor.
This work was done by Josette Bellan, Kenneth Harstad, and Nora Okong’o of Caltech for NASA’s Jet Propulsion Laboratory. To obtain a copy of the report, “Direct Numerical Simulations of LOX/H2 Temporal Mixing Layers Under Supercritical Conditions,” access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Physical Sciences category.
NPO-30179
This Brief includes a Technical Support Package (TSP).
DNS of a Supercritical H2/O2 Mixing Layer
(reference NPO-30179) is currently available for download from the TSP library.
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Overview
The document is a NASA Technical Support Package detailing a study on the direct numerical simulation (DNS) of a supercritical hydrogen/oxygen (H2/O2) mixing layer, focusing on the disintegration of liquid oxygen (LOX) in a liquid rocket engine environment. The research, conducted by Josette Bellan, Kenneth G. Harstad, and Nora Okong, addresses the challenges associated with liquid rocket propulsion, particularly the efficiency and stability issues that arise during combustion.
The study begins by outlining the fundamental processes occurring in liquid rocket combustion chambers, where LOX is injected and mixes with hydrogen in a turbulent manner, leading to combustion that produces water and other byproducts. The authors emphasize that LOX disintegration is distinct from traditional spray atomization, as it occurs under high pressure (approximately 20 MPa), which significantly influences the mixing dynamics.
The analysis identifies two primary factors contributing to the lack of transition in the mixing layer. First, the early formation of small turbulent scales disrupts the coherence of the vortices created through pairing, resulting in a weakened ultimate vortex. Second, regions of high density gradient magnitude, caused by the distortion of the initial density stratification and the mixing of the two species, inhibit the formation of small turbulent scales essential for effective mixing.
The document presents a comprehensive methodology, utilizing fluctuation-dissipation theory to model the fluid behavior at high pressures. The DNS approach allows for the resolution of all scales of flow, providing insights into the evolution of the mixing layer and the dynamics of LOX disintegration. The results are validated against experimental data, demonstrating qualitative similarities and enhancing the understanding of fluid disintegration under supercritical conditions.
In conclusion, this research represents a significant advancement in the study of LOX/H2 mixing layers, offering valuable insights that could lead to improved designs and operational efficiencies in liquid rocket propulsion systems. The findings underscore the importance of understanding the complex interactions within the mixing layer to address the challenges faced in rocket engine performance.
