Flame surface density modelling for the large eddy simulation of turbulent premixed flames
Author(s)
Ma, Terence Kwai Kin
Type
Thesis
Abstract
Large Eddy Simulation (LES) has become an increasingly useful tool for the prediction of turbulent
reactive flows with the increasing availability of cheaper and faster computing power.
In the context of premixed combustion, LES encounters the challenge of resolving the flame
thickness, which is normally smaller than the filter width used in typical engineering applications.
This thesis considers the Flame Surface Density (FSD) approach to provide closure
to the filtered LES reaction rate. The FSD can either be modelled algebraically (FSDA) or
determined through a transport equation (FSDT) and both approaches are investigated in the
LES of three different test cases. The first case explores the response of different FSDA models
towards changes in turbulence levels, and compares the instantaneous flame structures and
reaction rates predicted by FSDA and FSDT methods. The remaining cases examine the LES
of two turbulent premixed burners. A relatively large range of FSDA models are tested under
the same operating conditions for the first time, and the LES-FSDT equation is applied to
premixed flames that involve a higher level of geometric complexity than earlier work. Generally,
the results show that the performance of some FSDA models are inconsistent between
the two premixed burners, suggesting that the models may operate optimally under different
turbulent conditions. By contrast, the consistently good agreement of the FSDT results with
experiments suggests that the method has much potential in the LES modelling of turbulent
premixed flames. However, the improved FSDT predictions were dependent on the value of
the model constant within the sub-grid curvature model, and the value yielded an additional
dependency on filter width. For these reasons as well as for the higher computational expense,
the effective use of FSDT requires further development, while the application of the FSDA
models remains a viable alternative to the FSDT approach.
reactive flows with the increasing availability of cheaper and faster computing power.
In the context of premixed combustion, LES encounters the challenge of resolving the flame
thickness, which is normally smaller than the filter width used in typical engineering applications.
This thesis considers the Flame Surface Density (FSD) approach to provide closure
to the filtered LES reaction rate. The FSD can either be modelled algebraically (FSDA) or
determined through a transport equation (FSDT) and both approaches are investigated in the
LES of three different test cases. The first case explores the response of different FSDA models
towards changes in turbulence levels, and compares the instantaneous flame structures and
reaction rates predicted by FSDA and FSDT methods. The remaining cases examine the LES
of two turbulent premixed burners. A relatively large range of FSDA models are tested under
the same operating conditions for the first time, and the LES-FSDT equation is applied to
premixed flames that involve a higher level of geometric complexity than earlier work. Generally,
the results show that the performance of some FSDA models are inconsistent between
the two premixed burners, suggesting that the models may operate optimally under different
turbulent conditions. By contrast, the consistently good agreement of the FSDT results with
experiments suggests that the method has much potential in the LES modelling of turbulent
premixed flames. However, the improved FSDT predictions were dependent on the value of
the model constant within the sub-grid curvature model, and the value yielded an additional
dependency on filter width. For these reasons as well as for the higher computational expense,
the effective use of FSDT requires further development, while the application of the FSDA
models remains a viable alternative to the FSDT approach.
Date Issued
2013-02
Date Awarded
2013-07
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Van Wachem, Berend
Marquis, Andrew
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)