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Thin reaction zones in highly turbulent medium

Sabelnikov, V. A.; Yu, R. LU and Lipatnikov, A. N. (2019) In International Journal of Heat and Mass Transfer 128. p.1201-1205
Abstract

A big database (23 cases characterized by Damköhler number less than unity) created recently in 3D Direct Numerical Simulation (DNS) of propagation of a statistically one-dimensional and planar, dynamically passive reaction wave in statistically stationary, homogeneous, isotropic turbulence is analyzed. On the one hand, the DNS data well support the classical Damköhler expression, i.e., square-root dependence of a ratio of turbulent and laminar consumption velocities on the turbulent Reynolds number. On the other hand, contrary to the common interpretation of the Damköhler theory and, in particular, to the concept of distributed burning, the DNS data show that the reaction is still localized to thin zones even at Da as low as 0.01, with... (More)

A big database (23 cases characterized by Damköhler number less than unity) created recently in 3D Direct Numerical Simulation (DNS) of propagation of a statistically one-dimensional and planar, dynamically passive reaction wave in statistically stationary, homogeneous, isotropic turbulence is analyzed. On the one hand, the DNS data well support the classical Damköhler expression, i.e., square-root dependence of a ratio of turbulent and laminar consumption velocities on the turbulent Reynolds number. On the other hand, contrary to the common interpretation of the Damköhler theory and, in particular, to the concept of distributed burning, the DNS data show that the reaction is still localized to thin zones even at Da as low as 0.01, with the aforementioned ratio of the consumption velocities being mainly controlled by the reaction-zone-surface area. To reconcile these apparently inconsistent numerical findings, an alternative regime of propagation of reaction waves in a highly turbulent medium is analyzed, i.e., propagation of an infinitely thin reaction sheet is theoretically studied, with molecular mixing of the reactant and product being allowed in wide layers. In this limiting case, an increase in the consumption velocity by turbulence is solely controlled by an increase in the reaction-sheet area. Based on physical reasoning and estimates, the area is hypothesized to be close to the mean area of an inert iso-scalar surface at the same turbulent Reynolds number. This hypothesis leads to the aforementioned square-root dependence. Thus, both the DNS data and the developed theory show that a widely accepted hypothesis on penetration of small-scale turbulent eddies into reaction zones is not necessary to obtain the classical Damköhler scaling for turbulent consumption velocity.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Combustion regime diagram, DNS, Modeling, Premixed turbulent flame, Thin reaction zone
in
International Journal of Heat and Mass Transfer
volume
128
pages
5 pages
publisher
Pergamon
external identifiers
  • scopus:85053760572
ISSN
0017-9310
DOI
10.1016/j.ijheatmasstransfer.2018.09.098
language
English
LU publication?
yes
id
420c195d-3096-44f4-b4b2-c972c5f3465b
date added to LUP
2018-10-08 10:03:42
date last changed
2018-10-08 10:03:42
@article{420c195d-3096-44f4-b4b2-c972c5f3465b,
  abstract     = {<p>A big database (23 cases characterized by Damköhler number less than unity) created recently in 3D Direct Numerical Simulation (DNS) of propagation of a statistically one-dimensional and planar, dynamically passive reaction wave in statistically stationary, homogeneous, isotropic turbulence is analyzed. On the one hand, the DNS data well support the classical Damköhler expression, i.e., square-root dependence of a ratio of turbulent and laminar consumption velocities on the turbulent Reynolds number. On the other hand, contrary to the common interpretation of the Damköhler theory and, in particular, to the concept of distributed burning, the DNS data show that the reaction is still localized to thin zones even at Da as low as 0.01, with the aforementioned ratio of the consumption velocities being mainly controlled by the reaction-zone-surface area. To reconcile these apparently inconsistent numerical findings, an alternative regime of propagation of reaction waves in a highly turbulent medium is analyzed, i.e., propagation of an infinitely thin reaction sheet is theoretically studied, with molecular mixing of the reactant and product being allowed in wide layers. In this limiting case, an increase in the consumption velocity by turbulence is solely controlled by an increase in the reaction-sheet area. Based on physical reasoning and estimates, the area is hypothesized to be close to the mean area of an inert iso-scalar surface at the same turbulent Reynolds number. This hypothesis leads to the aforementioned square-root dependence. Thus, both the DNS data and the developed theory show that a widely accepted hypothesis on penetration of small-scale turbulent eddies into reaction zones is not necessary to obtain the classical Damköhler scaling for turbulent consumption velocity.</p>},
  author       = {Sabelnikov, V. A. and Yu, R. and Lipatnikov, A. N.},
  issn         = {0017-9310},
  keyword      = {Combustion regime diagram,DNS,Modeling,Premixed turbulent flame,Thin reaction zone},
  language     = {eng},
  month        = {01},
  pages        = {1201--1205},
  publisher    = {Pergamon},
  series       = {International Journal of Heat and Mass Transfer},
  title        = {Thin reaction zones in highly turbulent medium},
  url          = {http://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.09.098},
  volume       = {128},
  year         = {2019},
}