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Title: Flame thickness and conditional scalar dissipation rate in a premixed temporal turbulent reacting jet

Abstract

The flame structure corresponding to lean hydrogen–air premixed flames in intense sheared turbulence in the thin reaction zone regime is quantified from flame thickness and conditional scalar dissipation rate statistics, obtained from recent direct numerical simulation data of premixed temporally-evolving turbulent slot jet flames. It is found that, on average, these sheared turbulent flames are thinner than their corresponding planar laminar flames. Extensive analysis is performed to identify the reason for this counter-intuitive thinning effect. The factors controlling the flame thickness are analyzed through two different routes i.e., the kinematic route, and the transport and chemical kinetics route. The kinematic route is examined by comparing the statistics of the normal strain rate due to fluid motion with the statistics of the normal strain rate due to varying flame displacement speed or self-propagation. It is found that while the fluid normal straining is positive and tends to separate iso-scalar surfaces, the dominating normal strain rate due to self-propagation is negative and tends to bring the iso-scalar surfaces closer resulting in overall thinning of the flame. The transport and chemical kinetics route is examined by studying the non-unity Lewis number effect on the premixed flames. The effects from the kinematic route aremore » found to couple with the transport and chemical kinetics route. In addition, the intermittency of the conditional scalar dissipation rate is also examined. It is found to exhibit a unique non-monotonicity of the exponent of the stretched exponential function, conventionally used to describe probability density function tails of such variables. As a result, the non-monotonicity is attributed to the detailed chemical structure of hydrogen-air flames in which heat release occurs close to the unburnt reactants at near free-stream temperatures.« less

Authors:
 [1];  [2];  [1];  [3];  [2];  [4]
  1. Indian Institute of Science, Bangalore (India)
  2. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  3. The Univ. of New South Wales, Sydney, NSW (Australia)
  4. Princeton Univ., Princeton, NJ (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1372354
Report Number(s):
SAND-2017-2193J
Journal ID: ISSN 0010-2180; PII: S0010218017300743
Grant/Contract Number:
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Combustion and Flame
Additional Journal Information:
Journal Volume: 184; Journal Issue: C; Journal ID: ISSN 0010-2180
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; direct numerical simulations; detailed chemistry; flame thickness; conditional scalar dissipation rate; probability density functions

Citation Formats

Chaudhuri, Swetaprovo, Kolla, Hemanth, Dave, Himanshu L., Hawkes, Evatt R., Chen, Jacqueline H., and Law, Chung K. Flame thickness and conditional scalar dissipation rate in a premixed temporal turbulent reacting jet. United States: N. p., 2017. Web. doi:10.1016/j.combustflame.2017.02.027.
Chaudhuri, Swetaprovo, Kolla, Hemanth, Dave, Himanshu L., Hawkes, Evatt R., Chen, Jacqueline H., & Law, Chung K. Flame thickness and conditional scalar dissipation rate in a premixed temporal turbulent reacting jet. United States. doi:10.1016/j.combustflame.2017.02.027.
Chaudhuri, Swetaprovo, Kolla, Hemanth, Dave, Himanshu L., Hawkes, Evatt R., Chen, Jacqueline H., and Law, Chung K. Fri . "Flame thickness and conditional scalar dissipation rate in a premixed temporal turbulent reacting jet". United States. doi:10.1016/j.combustflame.2017.02.027.
@article{osti_1372354,
title = {Flame thickness and conditional scalar dissipation rate in a premixed temporal turbulent reacting jet},
author = {Chaudhuri, Swetaprovo and Kolla, Hemanth and Dave, Himanshu L. and Hawkes, Evatt R. and Chen, Jacqueline H. and Law, Chung K.},
abstractNote = {The flame structure corresponding to lean hydrogen–air premixed flames in intense sheared turbulence in the thin reaction zone regime is quantified from flame thickness and conditional scalar dissipation rate statistics, obtained from recent direct numerical simulation data of premixed temporally-evolving turbulent slot jet flames. It is found that, on average, these sheared turbulent flames are thinner than their corresponding planar laminar flames. Extensive analysis is performed to identify the reason for this counter-intuitive thinning effect. The factors controlling the flame thickness are analyzed through two different routes i.e., the kinematic route, and the transport and chemical kinetics route. The kinematic route is examined by comparing the statistics of the normal strain rate due to fluid motion with the statistics of the normal strain rate due to varying flame displacement speed or self-propagation. It is found that while the fluid normal straining is positive and tends to separate iso-scalar surfaces, the dominating normal strain rate due to self-propagation is negative and tends to bring the iso-scalar surfaces closer resulting in overall thinning of the flame. The transport and chemical kinetics route is examined by studying the non-unity Lewis number effect on the premixed flames. The effects from the kinematic route are found to couple with the transport and chemical kinetics route. In addition, the intermittency of the conditional scalar dissipation rate is also examined. It is found to exhibit a unique non-monotonicity of the exponent of the stretched exponential function, conventionally used to describe probability density function tails of such variables. As a result, the non-monotonicity is attributed to the detailed chemical structure of hydrogen-air flames in which heat release occurs close to the unburnt reactants at near free-stream temperatures.},
doi = {10.1016/j.combustflame.2017.02.027},
journal = {Combustion and Flame},
number = C,
volume = 184,
place = {United States},
year = {Fri Jul 07 00:00:00 EDT 2017},
month = {Fri Jul 07 00:00:00 EDT 2017}
}

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  • Abstract not provided.
  • No meaningful difference is observed between the predictions with the conditional velocity modeled by linear scaling and gradient diffusion assumption for the test flames under consideration. The AMC and Girimaji's model for CSDR show similar results, while the pdf integration method results in an asymmetric profile with some deviation from the other two. The difference tends to decrease as mixing proceeds, to result in a lower level of scalar dissipation at downstream locations. Reasonable agreement is achieved with measured scalar dissipation rates at different axial locations for the Sandia Flame D, while direct comparison is difficult due to radially averagedmore » pdfs and no measured scalar dissipation rates being available for the Sydney bluff-body flame.« less
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