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On the statistics of flame stretch in turbulent premixed jet flames in the thin reaction zone regime at varying Reynolds number

PROCEEDINGS OF THE COMBUSTION INSTITUTE (2019)

期刊

PROCEEDINGS OF THE COMBUSTION INSTITUTE

卷 37, 期 2, 页码 2451-2459

出版社

ELSEVIER SCIENCE INC

DOI: 10.1016/j.proci.2018.06.194

关键词

Turbulent premixed flames; Direct Numerical Simulation; Flame surface density; Flame stretch

类别

Thermodynamics Energy & Fuels Engineering, Chemical Engineering, Mechanical

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Direct Numerical Simulations (DNS) are conducted to study the statistics of flame surface stretch in turbulent jet premixed flames. Emphasis is placed on the rates of surface production and destruction and their scaling with the Reynolds number. Four lean methane/air turbulent slot jet flames are simulated at increasing Reynolds number and up to Re approximate to 22 x 10(3), based on the bulk velocity, slot width, and the reactants' properties. The Karlovitz number is held approximately constant and the flames fall in the thin reaction zone regime. The simulations feature finite rate chemistry and mixture-average transport. Our data indicate that the area of the flame surface increases up to the streamwise position corresponding to 80% of the average flame length and decreases afterwards as surface destruction overtakes production. It is observed that the tangential rate of strain is responsible for the production of flame surface in the mean and surface destruction is due to the curvature term. In addition, it is found that these two terms are both significantly larger than their difference, i.e., the net surface stretch.The statistics of the tangential strain rate are in good agreement with those for infinitesimal material surfaces in homogeneous isotropic turbulence. Once scaled by the Kolmogorov time scale, the means of both contributions to stretch are largely independent of location and equal across flames with different values of the Reynolds number. Surface destruction is due mostly to propagation into the reactants where the surface is folded into a cylindrical shape with the center of curvature on the side of the reactants. The joint statistics of the displacement speed and curvature of the reactive surface are nuanced, with the most probable occurrence being that of a negative displacement speed of a flat surface, while the surface averaged displacement speed is positive as expected. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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Physical effects of water droplets interacting with turbulent premixed flames: A Direct Numerical Simulation analysis

Josef Hasslberger, Gulcan Ozel-Erol, Nilanjan Chakraborty, Markus Klein, Stewart Cant

Summary: Three-dimensional carrier-phase Direct Numerical Simulations (DNS) combined with a Lagrangian representation of individual droplets were used to study the physical effects of liquid water mist interacting with laminar and turbulent premixed stoichiometric n-heptane/air flames. The study found that water droplets significantly reduce flame temperature and burning velocity, with the droplet size having a strongly non-linear impact on overall burning rate, while water loading has a more linear influence. The investigation also focused on the different regimes of droplet-flame interaction, particularly the influence of latent heat of vaporization.

COMBUSTION AND FLAME (2021)