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

Journal Article · Fri Jul 07 00:00:00 EDT 2017 · Combustion and Flame

DOI:https://doi.org/10.1016/j.combustflame.2017.02.027· OSTI ID:1372354

Chaudhuri, Swetaprovo ^[1]; Kolla, Hemanth ^[2]; Dave, Himanshu L. ^[1]; Hawkes, Evatt R. ^[3]; Chen, Jacqueline H. ^[2]; Law, Chung K. ^[4]

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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)

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.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; AC05-00OR22725
• OSTI ID: 1372354
• Alternate ID(s): OSTI ID: 1550438
• Report Number(s): SAND-2017-2193J; PII: S0010218017300743
• Journal Information: Combustion and Flame, Vol. 184, Issue C; ISSN 0010-2180
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
direct numerical simulations
detailed chemistry
flame thickness
conditional scalar dissipation rate
probability density functions