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A priori and a posteriori investigations for developing large eddy simulations of multi-species turbulent mixing under high-pressure conditions

Borghesi, Giulio and Bellan, Josette (2015) A priori and a posteriori investigations for developing large eddy simulations of multi-species turbulent mixing under high-pressure conditions. Physics of Fluids, 27 (3). Art. No. 035117. ISSN 1070-6631. http://resolver.caltech.edu/CaltechAUTHORS:20150507-104525329

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Abstract

A Direct Numerical Simulation (DNS) database was created representing mixing of species under high-pressure conditions. The configuration considered is that of a temporally evolving mixing layer. The database was examined and analyzed for the purpose of modeling some of the unclosed terms that appear in the Large Eddy Simulation (LES) equations. Several metrics are used to understand the LES modeling requirements. First, a statistical analysis of the DNS-database large-scale flow structures was performed to provide a metric for probing the accuracy of the proposed LES models as the flow fields obtained from accurate LESs should contain structures of morphology statistically similar to those observed in the filtered-and-coarsened DNS (FC-DNS) fields. To characterize the morphology of the large-scales structures, the Minkowski functionals of the iso-surfaces were evaluated for two different fields: the second-invariant of the rate of deformation tensor and the irreversible entropy production rate. To remove the presence of the small flow scales, both of these fields were computed using the FC-DNS solutions. It was found that the large-scale structures of the irreversible entropy production rate exhibit higher morphological complexity than those of the second invariant of the rate of deformation tensor, indicating that the burden of modeling will be on recovering the thermodynamic fields. Second, to evaluate the physical effects which must be modeled at the subfilter scale, an a priori analysis was conducted. This a priori analysis, conducted in the coarse-grid LES regime, revealed that standard closures for the filtered pressure, the filtered heat flux, and the filtered species mass fluxes, in which a filtered function of a variable is equal to the function of the filtered variable, may no longer be valid for the high-pressure flows considered in this study. The terms requiring modeling are the filtered pressure, the filtered heat flux, the filtered pressure work, and the filtered species mass fluxes. Improved models were developed based on a scale-similarity approach and were found to perform considerably better than the classical ones. These improved models were also assessed in an a posteriori study. Different combinations of the standard models and the improved ones were tested. At the relatively small Reynolds numbers achievable in DNS and at the relatively small filter widths used here, the standard models for the filtered pressure, the filtered heat flux, and the filtered species fluxes were found to yield accurate results for the morphology of the large-scale structures present in the flow. Analysis of the temporal evolution of several volume-averaged quantities representative of the mixing layer growth, and of the cross-stream variation of homogeneous-plane averages and second-order correlations, as well as of visualizations, indicated that the models performed equivalently for the conditions of the simulations. The expectation is that at the much larger Reynolds numbers and much larger filter widths used in practical applications, the improved models will have much more accurate performance than the standard one.


Item Type:Article
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http://dx.doi.org/10.1063/1.4916284DOIArticle
http://scitation.aip.org/content/aip/journal/pof2/27/3/10.1063/1.4916284PublisherArticle
Additional Information:© 2015 AIP Publishing LLC. Received 04 November 2014. Accepted 13 March 2015. Published online 31 March 2015. This study was conducted at the Jet Propulsion Laboratory (JPL) of the California Institute of Technology (Caltech), and this material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Gas Phase Chemical Physics in the Chemical Sciences, Geosciences and Biosciences Division) under Award No. DE-SC0002679, and the direction of Dr. Wade Sisk and Dr. Mark Pederson. The computational resources were provided by the National Energy Research Supercomputing Center of the Department of Energy, by the NASA Advanced Supercomputing at Ames Research Center, and by the JPL Supercomputing Center.
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Department of Energy (DOE)DE-SC0002679
Record Number:CaltechAUTHORS:20150507-104525329
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150507-104525329
Official Citation: A priori and a posteriori investigations for developing large eddy simulations of multi-species turbulent mixing under high-pressure conditions Giulio Borghesi and Josette Bellan Phys. Fluids 27, 035117 (2015); http://dx.doi.org/10.1063/1.4916284
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57333
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:07 May 2015 19:28
Last Modified:07 May 2015 19:28

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