This second of three reports on a computational study of a mixing layer laden with evaporating liquid drops presents the evaluation of Large Eddy Simulation (LES) models.
The LES models were evaluated on an existing database that had been generated using Direct Numerical Simulation (DNS). The DNS method and the database are described in the first report of this series, “Part 1 of a Computational Study of a Drop-Laden Mixing Layer” (NPO-30719), NASA Tech Briefs, Vol. 28, No.7 (July 2004), page 59. The LES equations, which are derived by applying a spatial filter to the DNS set, govern the evolution of the larger scales of the flow and can therefore be solved on a coarser grid. Consistent with the reduction in grid points, the DNS drops would be represented by fewer drops, called “computational drops” in the LES context. The LES equations contain terms that cannot be directly computed on the coarser grid and that must instead be modeled. Two types of models are necessary: (1) those for the filtered source terms representing the effects of drops on the filtered flow field and (2) those for the sub-grid scale (SGS) fluxes arising from filtering the convective terms in the DNS equations. All of the filtered-source-term models that were developed were found to overestimate the filtered source terms. For modeling the SGS fluxes, constant-coefficient Smagorinsky, gradient, and scale-similarity models were assessed and calibrated on the DNS database. The Smagorinsky model correlated poorly with the SGS fluxes, whereas the gradient and scale-similarity models were well correlated with the SGS quantities that they represented.
This work was done by Nora Okong'o and Josette Bellan of Caltech for NASA’s Jet Propulsion Laboratory. NPO-30732
This Brief includes a Technical Support Package (TSP).
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Overview
The document is a Technical Support Package for Part 2 of a computational study focused on a drop-laden mixing layer, referenced as NPO-30732 in NASA Tech Briefs. It is part of NASA's efforts to disseminate research findings that have potential applications in various technological, scientific, and commercial fields. The study aims to enhance understanding of the dynamics involved in mixing layers that contain droplets, which is significant for various aerospace applications, including fuel efficiency and emissions reduction in aircraft.
The document outlines the context and importance of the research, emphasizing its relevance to the aerospace industry. It highlights the role of drop-laden mixing layers in processes such as combustion and fluid dynamics, where the interaction between droplets and the surrounding fluid can significantly affect performance and efficiency.
Additionally, the Technical Support Package provides information on how to access further resources related to the study. It mentions the NASA Scientific and Technical Information (STI) Program Office, which offers a variety of publications and additional research materials. The STI Program Office can be contacted through their website or directly via phone and email for further inquiries.
The document also includes a notice regarding the copyright of the material, indicating that a royalty-free, nonexclusive license has been granted for government use, while any other use requires prior approval from the copyright holder. This emphasizes the importance of the information contained within the document and its intended use for government and research purposes.
Overall, the Technical Support Package serves as a resource for researchers and professionals interested in the dynamics of drop-laden mixing layers, providing foundational knowledge that could lead to advancements in aerospace technology and related fields. The study's findings are expected to contribute to improved understanding and optimization of processes involving droplets in fluid flows, which is crucial for enhancing the performance and sustainability of aerospace systems.
