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The effect of turbulence modelling on the CFD simulation of buoyant diffusion flames
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Liu, F. and Wen, Jennifer X. (2002) The effect of turbulence modelling on the CFD simulation of buoyant diffusion flames. Fire Safety Journal, Volume 37 (Number 2). pp. 125-150. doi:10.1016/S0379-7112(01)00022-4 ISSN 0379-7112.
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Official URL: http://dx.doi.org/10.1016/S0379-7112(01)00022-4
Abstract
For buoyant diffusion flames, both thermal and mechanical forces affect the turbulence mixing and combustion processes. The computation of individual turbulent heat flux View the MathML source and temperature variance View the MathML source are necessary and important. This raises questions about the use of traditional two equation k–ε type turbulence models in such applications. The present study is aimed at demonstrating the significant effects of turbulence modelling on the CFD simulation of buoyant diffusion flames. Two different turbulence models are used to compute McCaffrey's flame data. The first model is based on Hanjalic's (Proceedings of the 10th International Heat Transfer Conference, Vol. 1, 1994, p. 1) four-equation turbulence model, which has been modified by the present authors to account for turbulence anisotropy and coupled with an algebraic formulation for Reynolds stresses. The second is the low-Reynolds-number (LRN) k–ε model of Ince and Launder (Int. J. Heat Fluid Flow 10 (1989) 110). The predictions of both models for temperature gradients and buoyancy generation of turbulence are examined. It is found that the generalised gradient diffusion hypothesis formula in the LRN k–ε model severely under-predicts the buoyancy production of turbulent kinetic energy. Considering that the simple gradient diffusion formula in the standard k–ε model with buoyancy modification predicts even lower turbulence production due to buoyancy, fire modellers are cautioned about the use of the two equation k–ε type turbulence models in such applications. Furthermore, it is found that the velocity and temperature predictions by the two turbulence models differ as much as 20% along the centreline. The LRN k–ε model under-predicts the radial spreading rate of the flame, the temperature rise in the persistent flaming region and the lower portion of the intermittent flaming region. For the rest of the intermittent flaming region and the thermal plume, it over-predicts the temperature rise. The modified version of Hanjalic's turbulence model has achieved quantitatively good agreement with the experimental data on the predictions of velocity and temperature distributions. It has also given better predictions for the radial spreading rate of vertical flames and the flame shapes.
Item Type: | Journal Article | ||||
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Divisions: | Faculty of Science, Engineering and Medicine > Engineering > Engineering | ||||
Journal or Publication Title: | Fire Safety Journal | ||||
Publisher: | Pergamon | ||||
ISSN: | 0379-7112 | ||||
Official Date: | 2002 | ||||
Dates: |
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Volume: | Volume 37 | ||||
Number: | Number 2 | ||||
Page Range: | pp. 125-150 | ||||
DOI: | 10.1016/S0379-7112(01)00022-4 | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published | ||||
Access rights to Published version: | Restricted or Subscription Access |
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