A report presents a study addressing the question of which large-eddy simulation (LES) equations are appropriate for modeling the flow of evaporating drops of a multicomponent liquid in a gas (e.g., a spray of kerosene or diesel fuel in air). The LES equations are obtained from the direct numerical simulation (DNS) equations in which the solution is computed at all flow length scales, by applying a spatial low-pass filter. Thus, in LES the small scales are removed and replaced by terms that cannot be computed from the LES solution and instead must be modeled to retain the effect of the small scales into the equations. The mathematical form of these models is a subject of contemporary research.
For a single-component liquid, there is only one LES formulation, but this study revealed that for a multicomponent liquid, there are two non-equivalent LES formulations for the conservation equations describing the composition of the vapor. Criteria were proposed for selecting the multicomponent LES formulation that gives the best accuracy and increased computational efficiency. These criteria were applied in examination of filtered DNS databases to compute the terms in the LES equations. The DNS databases are from mixing layers of diesel and kerosene fuels. The comparisons resulted in the selection of one of the multicomponent LES formulations as the most promising with respect to all criteria.
This work was done by Josette Bellan and Laurent Selle of Caltech for NASA’s Jet Propulsion Laboratory. NPO-45065
This Brief includes a Technical Support Package (TSP).
Criteria for Modeling in LES of Multicomponent Fuel Flow
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Overview
The document titled "Criteria for Modeling in LES of Multicomponent Fuel Flow" (NPO-45065) is a technical support package from NASA's Jet Propulsion Laboratory that addresses the challenges associated with modeling multicomponent fuel behavior in large eddy simulations (LES). The primary problem identified is the lack of computationally efficient models for accurately computing the behavior of multicomponent fuels, which are critical in various aerospace applications.
To tackle this issue, the authors have developed unique equations that resolve all scales of the flow. However, for the sake of computational efficiency, the focus is on modeling only the large scales while filtering out the small scales. This filtering process leads to two non-equivalent formulations of the equations, which raises the question of how to determine which formulation is appropriate for a given scenario.
The novelty of this work lies in its approach to modeling fully multicomponent species flows. The equations derived for this model can be expressed in two equivalent ways, but once the small-scale effects are filtered out, the resulting equations diverge in their equivalence. This divergence necessitates a criterion to select the appropriate equation for modeling purposes.
The document references a related work titled “Modeling Requirements for Large Eddy Simulation of Multi-Component Fuel Two-Phase Flows Using Continuous Thermodynamics” by Laurent C. Selle and Josette Bellan, presented at the IILASS Americas 20th Annual Conference on Liquid Atomization and Spray Systems in May 2007. This reference underscores the academic and practical significance of the research.
In summary, the document provides a comprehensive overview of the methodologies developed for modeling multicomponent fuel flows in LES, emphasizing the importance of selecting the correct formulation after filtering small-scale effects. The insights gained from this research are expected to have broader technological, scientific, and commercial applications, particularly in the aerospace sector. The document also includes contact information for further inquiries and emphasizes compliance with U.S. export regulations, highlighting the proprietary nature of the information contained within.
