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Evaluation of assumed-PDF methods in two-phase flows using direct numerical simulation

Selle, L. C. and Bellan, J. (2007) Evaluation of assumed-PDF methods in two-phase flows using direct numerical simulation. Proceedings of the Combustion Institute, 31 (2). pp. 2273-2281. ISSN 1540-7489. doi:10.1016/j.proci.2006.07.004.

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The hypothesis of uncorrelated temperature (T) and vapor-fuel mass fraction (Y_v), frequently made when modeling reaction rates using assumed-PDF models, is examined utilizing transitional databases from direct numerical simulation (DNS) of three-dimensional mixing-layers two-phase (TP) flows with evaporation. Because the databases do not contain chemical reaction, which would further correlate variables, finding here a correlation between T and Y_v is sufficient for invalidating reaction rate modeling of the joint (T, Y_v) probability distribution function (PDF) as a product of the marginal PDFs. The databases comprise four multicomponent fuels, two mass loadings and two free-stream gas temperatures. For comparison, databases for single-phase (SP) flows are also analyzed at two initial Reynolds numbers. The examination is conducted in the mixing layer excluding the free streams and in a more restricted part of the mixing layer constituting its core. The analysis is performed at the DNS and large eddy simulation (LES) scales, and subgrid scale (SGS). To obtain the LES database, the DNS database is filtered, and an evaluation of the examined correlation at the LES and SGS scales is made at two filter sizes. At the DNS scale, T and Y_v are practically uncorrelated for SP flows, showing the weak influence of the perfect-gas equation of state, whereas for TP flows the correlation is strong and increases with mass loading indicating the powerful effect of the phase change. At the LES scale, the findings emulate those at the DNS scale. The fluctuations of the SGS scale are uncorrelated for SP flows, but the product of the marginal PDFs is different from the joint PDF. For TP flows, the fluctuations are correlated and the correlation increases with temperature, casting doubt on current assumed PDFs used to model chemistry in reacting sprays. These results are independent of filter size. The joint PDFs for TP and SP fluctuations are successfully modeled.

Item Type:Article
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Bellan, J.0000-0001-9218-7017
Additional Information:© 2006 The Combustion Institute. Published by Elsevier Inc. Available online 4 August 2006. This study was conducted at the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), under the partial sponsorship of the Donors of The Petroleum Research Fund administered by the American Chemical Society through a grant (to J.B.) for Caltech Post Doctoral Fellow (L.S.) support and of the US Department of Energy. We thank Victor Poupet of É cole Normale Supérieure for discussions on the form of the marginal PDF. Computational resources were provided by the supercomputing facility at JPL.
Funding AgencyGrant Number
American Chemical Society Petroleum Research FundUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Subject Keywords:Assumed-PDF methods in two-phase flows
Issue or Number:2
Record Number:CaltechAUTHORS:20171019-100315218
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Official Citation:L.C. Selle, J. Bellan, Evaluation of assumed-PDF methods in two-phase flows using direct numerical simulation, In Proceedings of the Combustion Institute, Volume 31, Issue 2, 2007, Pages 2273-2281, ISSN 1540-7489, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82483
Deposited By: Tony Diaz
Deposited On:19 Oct 2017 18:04
Last Modified:15 Nov 2021 19:50

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