skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Can we characterize turbulence in premixed flames?

Abstract

Modeling of premixed turbulent combustion involves averaging reaction rates in turbulent flows. The focus of most approaches to resolving this problem has been placed on determining the dependence of the mean rate w of product creation on the laminar flame speed S{sub L}, the rms turbulence velocity u', etc. The goal of the present work is to draw attention to another issue: May the input quantity u{sup '} for a model of w= w(u'/S{sub L},..) be considered to be known? The point is that heat release substantially affects turbulence and, hence, turbulence characteristics in premixed flames should be modeled. However, standard moment methods for numerically simulating turbulent flows do not allow us to evaluate the true turbulence characteristics in a flame. For instance, the Reynolds stresses in premixed flames are affected not only by turbulence itself, but also by velocity jump across flamelets. A common way to resolving this problem consists of considering the Reynolds stresses conditioned on unburned (or burned) mixture to be the true turbulence characteristics. In the present paper, this widely accepted but never proved hypothesis is put into question, first, by considering simple model constant-density problems (flame motion in an oscillating one-dimensional laminar flow; flame stabilizedmore » in a periodic shear, one-dimensional, laminar flow; turbulent mixing). In all the cases, the magnitude of velocity fluctuations, calculated using the conditioned Reynolds stresses, is affected by the intermittency of reactants and products and, hence, is not the true rms velocity. Second, the above claim is further supported by comparing balance equations for the mean and conditioned Reynolds stresses. The conditioned Reynolds stresses do not characterize the true turbulence in flames, because conditional averaging cuts off flow regions characterized by either high or low velocities. (author)« less

Authors:
 [1]
  1. Department of Applied Mechanics, Chalmers University of Technology, Gothenburg, 412 96 (Sweden)
Publication Date:
OSTI Identifier:
21177448
Resource Type:
Journal Article
Journal Name:
Combustion and Flame
Additional Journal Information:
Journal Volume: 156; Journal Issue: 6; Other Information: Elsevier Ltd. All rights reserved; Journal ID: ISSN 0010-2180
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LAMINAR FLAMES; REYNOLDS NUMBER; TURBULENCE; COMBUSTION; VELOCITY; LAMINAR FLOW; STRESSES; TURBULENT FLOW; PERIODICITY; MOMENTS METHOD; FLAME PROPAGATION; ONE-DIMENSIONAL CALCULATIONS; COMBUSTION KINETICS; FLUCTUATIONS; HEAT; SIMULATION; HYPOTHESIS; MATHEMATICAL MODELS; SHEAR; Premixed turbulent combustion

Citation Formats

Lipatnikov, A N. Can we characterize turbulence in premixed flames?. United States: N. p., 2009. Web. doi:10.1016/J.COMBUSTFLAME.2009.01.002.
Lipatnikov, A N. Can we characterize turbulence in premixed flames?. United States. https://doi.org/10.1016/J.COMBUSTFLAME.2009.01.002
Lipatnikov, A N. 2009. "Can we characterize turbulence in premixed flames?". United States. https://doi.org/10.1016/J.COMBUSTFLAME.2009.01.002.
@article{osti_21177448,
title = {Can we characterize turbulence in premixed flames?},
author = {Lipatnikov, A N},
abstractNote = {Modeling of premixed turbulent combustion involves averaging reaction rates in turbulent flows. The focus of most approaches to resolving this problem has been placed on determining the dependence of the mean rate w of product creation on the laminar flame speed S{sub L}, the rms turbulence velocity u', etc. The goal of the present work is to draw attention to another issue: May the input quantity u{sup '} for a model of w= w(u'/S{sub L},..) be considered to be known? The point is that heat release substantially affects turbulence and, hence, turbulence characteristics in premixed flames should be modeled. However, standard moment methods for numerically simulating turbulent flows do not allow us to evaluate the true turbulence characteristics in a flame. For instance, the Reynolds stresses in premixed flames are affected not only by turbulence itself, but also by velocity jump across flamelets. A common way to resolving this problem consists of considering the Reynolds stresses conditioned on unburned (or burned) mixture to be the true turbulence characteristics. In the present paper, this widely accepted but never proved hypothesis is put into question, first, by considering simple model constant-density problems (flame motion in an oscillating one-dimensional laminar flow; flame stabilized in a periodic shear, one-dimensional, laminar flow; turbulent mixing). In all the cases, the magnitude of velocity fluctuations, calculated using the conditioned Reynolds stresses, is affected by the intermittency of reactants and products and, hence, is not the true rms velocity. Second, the above claim is further supported by comparing balance equations for the mean and conditioned Reynolds stresses. The conditioned Reynolds stresses do not characterize the true turbulence in flames, because conditional averaging cuts off flow regions characterized by either high or low velocities. (author)},
doi = {10.1016/J.COMBUSTFLAME.2009.01.002},
url = {https://www.osti.gov/biblio/21177448}, journal = {Combustion and Flame},
issn = {0010-2180},
number = 6,
volume = 156,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2009},
month = {Mon Jun 15 00:00:00 EDT 2009}
}