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Title: Modeling of scalar dissipation in partially premixed turbulent flames

Abstract

The question of the closure of scalar dissipation terms for both passive and reactive scalars is addressed. In a first step of the analysis, modeled transport equations for the mean reactive scalar dissipation are reviewed in the two limiting cases of (i) the flamelet regime and (ii) the thickened flame regime of turbulent premixed combustion. The corresponding asymptotic algebraic closures obtained for large values of the turbulent Reynolds Re{sub T}, i.e., eddy breakup and linear relaxation model for scalar fluctuations decay, are recovered. These two limiting closures are then used to build a general algebraic closure of the mean dissipation of reactive scalar fluctuations. The resulting expression is applicable to modeling turbulent premixed combustion whatever the combustion regime. In a second step, the same strategy leads to the development of an algebraic closure for partially premixed situations, a situation requiring the use of at least two variables. In this process, a relationship between reactive, passive, and cross-scalar dissipations is derived. This general result is then simplified to elaborate new closed expressions of mean dissipation terms. There are applicable to a wide range of conditions, from premixed to partially premixed situations and from the flamelet to the thickened flame regime. (author)

Authors:
; ;  [1]
  1. LCD UPR 9028 du CNRS, ENSMA Poitiers (France)
Publication Date:
OSTI Identifier:
20880650
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 149; Journal Issue: 1-2; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; COMBUSTION; SCALARS; CONVERGENCE; SIMULATION; FLAMES; FLUCTUATIONS; REYNOLDS NUMBER; TRANSPORT THEORY; RELAXATION; TURBULENCE; ASYMPTOTIC SOLUTIONS; MATHEMATICAL MODELS

Citation Formats

Mura, Arnaud, Robin, Vincent, and Champion, Michel. Modeling of scalar dissipation in partially premixed turbulent flames. United States: N. p., 2007. Web. doi:10.1016/J.COMBUSTFLAME.2006.11.004.
Mura, Arnaud, Robin, Vincent, & Champion, Michel. Modeling of scalar dissipation in partially premixed turbulent flames. United States. doi:10.1016/J.COMBUSTFLAME.2006.11.004.
Mura, Arnaud, Robin, Vincent, and Champion, Michel. Sun . "Modeling of scalar dissipation in partially premixed turbulent flames". United States. doi:10.1016/J.COMBUSTFLAME.2006.11.004.
@article{osti_20880650,
title = {Modeling of scalar dissipation in partially premixed turbulent flames},
author = {Mura, Arnaud and Robin, Vincent and Champion, Michel},
abstractNote = {The question of the closure of scalar dissipation terms for both passive and reactive scalars is addressed. In a first step of the analysis, modeled transport equations for the mean reactive scalar dissipation are reviewed in the two limiting cases of (i) the flamelet regime and (ii) the thickened flame regime of turbulent premixed combustion. The corresponding asymptotic algebraic closures obtained for large values of the turbulent Reynolds Re{sub T}, i.e., eddy breakup and linear relaxation model for scalar fluctuations decay, are recovered. These two limiting closures are then used to build a general algebraic closure of the mean dissipation of reactive scalar fluctuations. The resulting expression is applicable to modeling turbulent premixed combustion whatever the combustion regime. In a second step, the same strategy leads to the development of an algebraic closure for partially premixed situations, a situation requiring the use of at least two variables. In this process, a relationship between reactive, passive, and cross-scalar dissipations is derived. This general result is then simplified to elaborate new closed expressions of mean dissipation terms. There are applicable to a wide range of conditions, from premixed to partially premixed situations and from the flamelet to the thickened flame regime. (author)},
doi = {10.1016/J.COMBUSTFLAME.2006.11.004},
journal = {Combustion and Flame},
number = 1-2,
volume = 149,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The scalar dissipation rate signifies the local mixing rate and thus plays a vital role in the modeling of reaction rate in turbulent flames. The local mixing rate is influenced by the turbulence, the chemical, and the molecular diffusion processes which are strongly coupled in turbulent premixed flames. Thus, a model for the mean scalar dissipation rate, and hence the mean reaction rate, should include the contributions of these processes. Earlier models for the scalar dissipation rate include only a turbulence time scale. In this study, we derive exact transport equations for the instantaneous and the mean scalar dissipation rates.more » Using these equations, a simple algebraic model for the mean scalar dissipation rate is obtained. This model includes a chemical as well as a turbulence time scale and its prediction compares well with direct numerical simulation results. Reynolds-averaged Navier-Stokes calculations of a test flame using the model obtained here show that the contribution of dilatation to local turbulent mixing rate is important to predict the propagation phenomenon.« less
  • Dissipation spectra of velocity and reactive scalars—temperature and fuel mass fraction—in turbulent premixed flames are studied using direct numerical simulation data of a temporally evolving lean hydrogen-air premixed planar jet (PTJ) flame and a statistically stationary planar lean methane-air (SP) flame. Furthermore, the equivalence ratio in both cases was 0.7, the pressure 1 atm while the unburned temperature was 700 K for the hydrogen-air PTJ case and 300 K for methane-air SP case, that resulted in data sets with a density ratio of 3 and 5, respectively. The turbulent Reynolds numbers for the cases ranged from 200 to 428.4, themore » Damköhler number from 3.1 to 29.1, and the Karlovitz number from 0.1 to 4.5. The dissipation spectra collapse when normalized by the respective Favre-averaged dissipation rates. But, the normalized dissipation spectra in all the cases deviate noticeably from those predicted by classical scaling laws for constant-density turbulent flows and bear a clear influence of the chemical reactions on the dissipative range of the energy cascade.« less