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Direct simulation of non-premixed flame extinction in a methane–air jet with reduced chemistry

Pantano, C. (2004) Direct simulation of non-premixed flame extinction in a methane–air jet with reduced chemistry. Journal of Fluid Mechanics, 514 . pp. 231-270. ISSN 0022-1120. http://resolver.caltech.edu/CaltechAUTHORS:PANjfm04

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Abstract

A three-dimensional direct numerical simulation (DNS) study of a spatially evolving planar turbulent reacting jet is reported. Combustion of methane with air is modelled using a four-step reduced mechanism in the non-premixed regime. A total of eight chemical species are integrated in time along with the fluid mechanical fields. The solution of the compressible Navier–Stokes equations is obtained numerically for moderately low Mach number. A large computational grid, with 100 million grid points, is required in order to resolve the flame. The cold flow Reynolds number is 3000. The focus of the study is to investigate the dynamics of extinction fronts in three-dimensional turbulent flows. A novel data reduction and identification algorithm was developed to postprocess the large DNS database and extract the shape of the evolving flame surface including its edges and their propagation velocity. The joint probability density function (p.d.f.) of edge velocity and scalar dissipation was obtained and the results indicate that the three-dimensional flame edges propagate with a velocity that is largely controlled by the local rate of scalar dissipation, or equivalently in terms of the local Damköhler number at the flame edge, as predicted by theory. Naturally, the effects of unsteadiness in this flow produce a broad joint p.d.f. The statistics collected also suggest that the mean value of the hydrogen radical reaction rate are very small in the turbulent regions of the flow owing to the functional form of the hydrogen radical reaction rate itself. The consequence of these results in the context of turbulent combustion modelling is discussed. Additional statistical and morphological information of the flame is provided.


Item Type:Article
Additional Information:Copyright © 2004 Cambridge University Press. "Reprinted with the permission of Cambridge University Press." Received November 10 2003; revised April 6 2004. This work was supported in part by the ASC program of the Department of Energy under subcontract no. B341492 of DOE contract W-7405-ENG-48. The author would like to thank S. Lombeyda of the Center for Advanced Computing Research at Caltech for generating the three-dimensional hydrogen radical mass fraction figures. The author would also like to thank Professor D.I. Pullin for innumerable discussions and for reading and suggesting improvements to the manuscript. Additionally, the author would like to thank the referees for many comments.
Subject Keywords:DIRECT NUMERICAL-SIMULATION; TURBULENT NONPREMIXED FLAMES; DIFFUSION FLAMES; EDGE-FLAMES; HEAT RELEASE; MIXING LAYERS; ASYMPTOTIC ANALYSIS; SCALAR DISSIPATION; TRIPLE FLAME; REACTIVE FLOWS
Record Number:CaltechAUTHORS:PANjfm04
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:PANjfm04
Alternative URL:http://dx.doi.org/10.1017/S0022112004000266
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7262
Collection:CaltechAUTHORS
Deposited By: Lindsay Cleary
Deposited On:24 Jan 2007
Last Modified:26 Dec 2012 09:30

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