This report presents an analysis of a database from computational simulations of a droplet-laden mixing layer (i.e., evaporating droplets of a liquid fuel in air) undergoing a transition to turbulence. The basic governing equations were those of transport of discrete droplets through a flowing gas; the droplets were followed in a Lagrangian frame whereas the gas was followed in an Eulerian frame. The analysis involved the extraction of subgrid scale (SGS) models from flow fields generated using the direct numerical simulation (DNS) approach, in which the governing equations are solved directly at the relevant length scales.
This work was done by Josette Bellan and Nora Okong'o of Caltech for NASA's Jet Propulsion Laboratory. To obtain a copy of the report, " A Priori Subgrid Analysis of Temporal Mixing Layers with Evaporating Droplets," access the Technical Support Package (TSP) free on0line at www.nasatech.com/tsp under the Physical Sciences category
NPO-20791
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Subgrid Analysis of Mixing Layer With Evaporating Droplets
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Overview
The document is a NASA Technical Support Package that focuses on the subgrid analysis of mixing layers containing evaporating droplets, prepared by the Jet Propulsion Laboratory. It addresses the complexities of computational simulations that involve droplet-laden mixing layers transitioning into turbulence, a phenomenon critical in various engineering and environmental applications.
The primary objective of the report is to develop and refine subgrid scale models derived from direct numerical simulations (DNS). These models are essential for improving large-eddy simulations (LES), which are widely used in turbulence modeling. The presence of droplets in a gas phase introduces additional complexities, as the interactions between the droplets and the surrounding fluid can significantly influence the flow dynamics and turbulence characteristics.
The document outlines the methodology employed in the simulations, detailing how the DNS captures the intricate behaviors of the mixing layers and the evaporating droplets. It emphasizes the importance of accurately modeling the gas-phase variables, as they are crucial for predicting the overall behavior of the system. The report also discusses the challenges faced in the simulations, such as the need for high-resolution data to capture the small-scale interactions between droplets and the turbulent flow.
Furthermore, the report highlights the potential applications of the research findings, which can extend to various fields, including combustion, atmospheric science, and industrial processes where droplet dynamics play a significant role. By enhancing the understanding of how droplets interact with turbulent flows, the research aims to contribute to the development of more efficient and effective models for predicting the behavior of such systems.
In summary, this document serves as a comprehensive exploration of the subgrid analysis of mixing layers with evaporating droplets, providing valuable insights into the modeling of complex fluid dynamics. It underscores the significance of direct numerical simulations in informing and improving large-eddy simulations, ultimately aiming to advance the understanding of turbulence in droplet-laden flows.
