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    The blow-off mechanism of a bluff-body stabilized laminar premixed flame

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    Type
    Article
    Authors
    Kedia, Kushal S. cc
    Ghoniem, Ahmed F.
    KAUST Grant Number
    KUS-11-010-01
    Date
    2015-04
    Permanent link to this record
    http://hdl.handle.net/10754/599880
    
    Metadata
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    Abstract
    © 2014 The Combustion Institute. The objective of this work is to investigate the dynamics leading to blow-off of a laminar premixed flame stabilized on a confined bluff-body using high fidelity numerical simulations. We used unsteady, fully resolved, two-dimensional simulations with detailed chemical kinetics and species transport for methane-air combustion. The flame-wall interaction between the hot reactants and the heat conducting bluff-body was accurately captured by incorporating the conjugate heat exchange between them. Simulations showed a shear-layer stabilized flame just downstream of the bluff-body, with a recirculation zone formed by the products of combustion. The flame was negatively stretched along its entire length, primarily dominated by the normal component of the strain. Blow-off was approached by decreasing the mixture equivalence ratio, at a fixed Reynolds number, of the incoming flow. A flame is stable (does not undergo blow-off) when (1) flame displacement speed is equal to the flow speed and (2) the gradient of the flame displacement speed normal to its surface is higher than the gradient of the flow speed along the same direction. As the equivalence ratio is reduced, the difference between the former and the latter shrinks until the dynamic stability condition (2) is violated, leading to blow-off. Blow-off initiates at a location where this is first violated along the flame. Our results showed that this location was far downstream from the flame anchoring zone, near the end of the recirculation zone. Blow-off started by flame pinching separating the flame into an upstream moving (carried within the recirculation zone) and a downstream convecting (detached from the recirculation zone) flame piece. Within the range of operating conditions investigated, the conjugate heat exchange with the bluff-body had no impact on the flame blow-off.
    Citation
    Kedia KS, Ghoniem AF (2015) The blow-off mechanism of a bluff-body stabilized laminar premixed flame. Combustion and Flame 162: 1304–1315. Available: http://dx.doi.org/10.1016/j.combustflame.2014.10.017.
    Sponsors
    This work was supported by King Abdullah University of Science and Technology (KAUST) Award Number KUS-11-010-01. We would like to acknowledge Dr. Habib Najm, Dr. Cosmin Safta and Dr. Jaideep Ray (Combustion Research Facility, Sandia National Laboratories, Livermore, CA, USA) for their major contribution towards the SAMR tool development. Special thanks to Dr. Santosh Shanbhogue (Research Scientist, Reacting Gas Dynamics Laboratory, MIT, Cambridge, MA, USA) for his invaluable inputs and suggestions.
    Publisher
    Elsevier BV
    Journal
    Combustion and Flame
    DOI
    10.1016/j.combustflame.2014.10.017
    ae974a485f413a2113503eed53cd6c53
    10.1016/j.combustflame.2014.10.017
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