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Characterization and modeling of premixed turbulent n-heptane flames in the thin reaction zone regime

Citation

Savard, Bruno (2015) Characterization and modeling of premixed turbulent n-heptane flames in the thin reaction zone regime. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9GM858F. http://resolver.caltech.edu/CaltechTHESIS:05282015-154709861

Abstract

n-heptane/air premixed turbulent flames in the high-Karlovitz portion of the thin reaction zone regime are characterized and modeled in this thesis using Direct Numerical Simulations (DNS) with detailed chemistry. In order to perform these simulations, a time-integration scheme that can efficiently handle the stiffness of the equations solved is developed first. A first simulation with unity Lewis number is considered in order to assess the effect of turbulence on the flame in the absence of differential diffusion. A second simulation with non-unity Lewis numbers is considered to study how turbulence affects differential diffusion. In the absence of differential diffusion, minimal departure from the 1D unstretched flame structure (species vs. temperature profiles) is observed. In the non-unity Lewis number case, the flame structure lies between that of 1D unstretched flames with "laminar" non-unity Lewis numbers and unity Lewis number. This is attributed to effective Lewis numbers resulting from intense turbulent mixing and a first model is proposed. The reaction zone is shown to be thin for both flames, yet large chemical source term fluctuations are observed. The fuel consumption rate is found to be only weakly correlated with stretch, although local extinctions in the non-unity Lewis number case are well correlated with high curvature. These results explain the apparent turbulent flame speeds. Other variables that better correlate with this fuel burning rate are identified through a coordinate transformation. It is shown that the unity Lewis number turbulent flames can be accurately described by a set of 1D (in progress variable space) flamelet equations parameterized by the dissipation rate of the progress variable. In the non-unity Lewis number flames, the flamelet equations suggest a dependence on a second parameter, the diffusion of the progress variable. A new tabulation approach is proposed for the simulation of such flames with these dimensionally-reduced manifolds.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:premixed flames, turbulent flames, chemistry modeling, time-integration, n-heptane, direct numerical simulations, high Karlovitz, chemistry tabulation
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aerospace Engineering
Awards:Hans G. Hornung Prize, 2015
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Blanquart, Guillaume
Thesis Committee:
  • Colonius, Timothy E. (chair)
  • McKeon, Beverley J.
  • Shepherd, Joseph E.
  • Blanquart, Guillaume
Defense Date:12 May 2015
Non-Caltech Author Email:bruno.savard (AT) gmail.com
Funders:
Funding AgencyGrant Number
Air Force Office of Scientific ResearchFA9550- 12-1-0144
NSERC of CanadaPostgraduate Scholarship D
Office of Science of the U.S. Department of EnergyDE-AC02-05CH11231
Record Number:CaltechTHESIS:05282015-154709861
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05282015-154709861
DOI:10.7907/Z9GM858F
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.combustflame.2014.12.020DOIBroken reaction zone and differential diffusion effects in high Karlovitz n-C7H16 premixed turbulent flames
http://dx.doi.org/10.1016/j.combustflame.2013.12.014DOIAn a priori model for the effective species Lewis numbers in premixed turbulent flames
http://dx.doi.org/10.1016/j.proci.2014.06.133DOIStructure of a high Karlovitz n-C7H16 premixed turbulent flame
http://dx.doi.org/10.1016/j.jcp.2015.04.018DOIA computationally-efficient, semi-implicit, iterative method for the time-integration of reacting flows with stiff chemistry
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8904
Collection:CaltechTHESIS
Deposited By: Bruno Savard
Deposited On:02 Jun 2015 15:21
Last Modified:12 Apr 2016 20:56

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