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|Title: ||CFD modelling of turbulent combustion and heat transfer|
|Authors: ||Alim, Md Abdul|
|Issue Date: ||2004|
|Publisher: ||© Md Abdul Alim|
|Abstract: ||This thesis is concerned with the development and implementation of computational
fluid dynamics (CFD) based prediction methodologies for turbulent reacting flows with
principal application to turbulent diffusion flame combustors. Numerical simulation of
combustion problems involve strong coupling between chemistry, transport and fluid
dynamics. The works accomplished in this study can be separated mainly into three
distinct areas: i) assessment of the performance of turbulent combustion models and to
implement suitable submodels for combustion and flame behaviour into CFD code; ii)
Conducting CFD modelling of turbulent diffusion flames, radiation heat loss from
combustion and flame zones; and iii) modelling of pollutants like NOx (oxides of
nitrogen), identification of the effect of radiation heat loss on NOx formation.
The combustion models studied are the flame-sheet, equilibrium, eddy break-up and
laminar flamelet models. An in-house CFD code is developed and combustion models
are implemented. The basic numerical issues involving the discretisation schemes are
addressed by employing three discretisation schemes namely, hybrid, power law and TVD (total variation diminishing) schemes.
The combustion of different fuels ranging from simple H2/N2 and CO/H2/N2 to complex
CH4/H2 are investigated for different inlet velocities and boundary conditions. The
performances of the combustion models are analysed for these fuels. The configurations
used for the validation and assessment of the combustion models are co-flowing jet
flames and bluff body burner stabilized flames. The high quality experimental databases
available from Sandia national laboratories, the University of Sydney and other reported
measurements are used for the purpose of evaluating the combustion models. The
predicted results demonstrate the effects of turbulent mixing and the effects of chemical
reactions on the combustion models.
The calculations show that all the combustion models like flame-sheet and equilibrium
models are found to be inadequate even for the near equilibrium flames. Although the
equilibrium chemistry model is capable of predicting the mixture fraction, temperature
and concentrations of major and minor species, the predictive accuracy is found to be
inadequate specially, when compared to the experimental data. In situations, where
finite rate chemistry effects are important the laminar flamelet model is a good choice. The key contributions of this thesis are as follows:
1) Modification of in-house CFD code for turbulent reacting flow and development of
CFD based iterative scheme for the turbulent diffusion flames to account for
radiation heat loss from combustion and flame zones.
2) Thorough assessment of turbulent combustion modelling techniques for different
cases of diffusion flames, demonstration of the importance of differential diffusion
in the flamelet modelling of combustion and comprehensive validation 3) Demonstration of the importance of radiation heat loss in the modelling of turbulent
combustion, implementation of radiation modelling in the three cases of diffusion
flames and comprehensive validation of CFD based combustion radiation results.
4) Development of modelling strategy for the pollutants like oxides of nitrogen (NOx),
implementation of NOx modelling in the different flames cases and identified the
effect of radiation heat loss on NOx formation.
The works addressed in this thesis are presented with the applications to turbulent
diffusion flame combustors. However, these works can easily be extended to the
industrial applications and applied to a large variety of other challenging domains.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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