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Direct numerical simulations of a high Karlovitz number laboratory premixed jet flame - An analysis of flame stretch and flame thickening

Wang, Haiou; Hawkes, Evatt R.; Chen, Jacqueline H.; Zhou, Bo LU ; Li, Zhongshan LU and Aldén, Marcus LU (2017) In Journal of Fluid Mechanics 815. p.511-536
Abstract

This article reports an analysis of the first detailed chemistry direct numerical simulation (DNS) of a high Karlovitz number laboratory premixed flame. The DNS results are first compared with those from laser-based diagnostics with good agreement. The subsequent analysis focuses on a detailed investigation of the flame area, its local thickness and their rates of change in isosurface following reference frames, quantities that are intimately connected. The net flame stretch is demonstrated to be a small residual of large competing terms: The positive tangential strain term and the negative curvature stretch term. The latter is found to be driven by flame speed-curvature correlations and dominated in net by low probability highly curved... (More)

This article reports an analysis of the first detailed chemistry direct numerical simulation (DNS) of a high Karlovitz number laboratory premixed flame. The DNS results are first compared with those from laser-based diagnostics with good agreement. The subsequent analysis focuses on a detailed investigation of the flame area, its local thickness and their rates of change in isosurface following reference frames, quantities that are intimately connected. The net flame stretch is demonstrated to be a small residual of large competing terms: The positive tangential strain term and the negative curvature stretch term. The latter is found to be driven by flame speed-curvature correlations and dominated in net by low probability highly curved regions. Flame thickening is demonstrated to be substantial on average, while local regions of flame thinning are also observed. The rate of change of the flame thickness (as measured by the scalar gradient magnitude) is demonstrated, analogously to flame stretch, to be a competition between straining tending to increase gradients and flame speed variations in the normal direction tending to decrease them. The flame stretch and flame thickness analyses are connected by the observation that high positive tangential strain rate regions generally correspond with low curvature regions; these regions tend to be positively stretched in net and are relatively thinner compared with other regions. High curvature magnitude regions (both positive and negative) generally correspond with lower tangential strain; these regions are in net negatively stretched and thickened substantially.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
combustion, reacting flows, turbulent reacting flows
in
Journal of Fluid Mechanics
volume
815
pages
26 pages
publisher
Cambridge University Press
external identifiers
  • scopus:85013635110
  • wos:000395426400020
ISSN
0022-1120
DOI
10.1017/jfm.2017.53
language
English
LU publication?
yes
id
13c41647-afc5-4bb3-b88a-2d455b8c9ba2
date added to LUP
2017-03-08 09:49:23
date last changed
2018-05-13 04:29:36
@article{13c41647-afc5-4bb3-b88a-2d455b8c9ba2,
  abstract     = {<p>This article reports an analysis of the first detailed chemistry direct numerical simulation (DNS) of a high Karlovitz number laboratory premixed flame. The DNS results are first compared with those from laser-based diagnostics with good agreement. The subsequent analysis focuses on a detailed investigation of the flame area, its local thickness and their rates of change in isosurface following reference frames, quantities that are intimately connected. The net flame stretch is demonstrated to be a small residual of large competing terms: The positive tangential strain term and the negative curvature stretch term. The latter is found to be driven by flame speed-curvature correlations and dominated in net by low probability highly curved regions. Flame thickening is demonstrated to be substantial on average, while local regions of flame thinning are also observed. The rate of change of the flame thickness (as measured by the scalar gradient magnitude) is demonstrated, analogously to flame stretch, to be a competition between straining tending to increase gradients and flame speed variations in the normal direction tending to decrease them. The flame stretch and flame thickness analyses are connected by the observation that high positive tangential strain rate regions generally correspond with low curvature regions; these regions tend to be positively stretched in net and are relatively thinner compared with other regions. High curvature magnitude regions (both positive and negative) generally correspond with lower tangential strain; these regions are in net negatively stretched and thickened substantially.</p>},
  author       = {Wang, Haiou and Hawkes, Evatt R. and Chen, Jacqueline H. and Zhou, Bo and Li, Zhongshan and Aldén, Marcus},
  issn         = {0022-1120},
  keyword      = {combustion,reacting flows,turbulent reacting flows},
  language     = {eng},
  month        = {03},
  pages        = {511--536},
  publisher    = {Cambridge University Press},
  series       = {Journal of Fluid Mechanics},
  title        = {Direct numerical simulations of a high Karlovitz number laboratory premixed jet flame - An analysis of flame stretch and flame thickening},
  url          = {http://dx.doi.org/10.1017/jfm.2017.53},
  volume       = {815},
  year         = {2017},
}