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UBC Theses and Dissertations

Application of the Uniform Conditional State model to numerical simulation of turbulent combustion Taylor, Sonia Ruth


Combustion of hydrocarbon fuels plays a major role in meeting world energy de- mand and is expected to continue to do so for the foreseeable future. Numerical simulation of combustion is an important tool that can be used in the design of combustion devices. Combustion simulation is highly challenging due to the com- plexity of the turbulence and chemical processes that occur, and modeling these phenomena as well as their interactions is a field of ongoing research. This work aims to improve the tools available for combustion simulation, so that cleaner, more efficient engines can be developed in the future. The specific focus of this work is a model for turbulence-chemistry interaction called Uniform Conditional State (UCS), which is related to conditional moment closure (CMC) methods. As with CMC, the UCS model uses conditional averaging to achieve chemical closure. However, the UCS model is unique in assuming that with sufficient conditioning, the conditional fields are spatially homogeneous, and can therefore be solved for on a conditional domain separate from the spatial domain. The two research chapters focus on the validation of the UCS model. A study examining the effect of using a model PDF when mapping between the conditional and spatial domains in the context of non-premixed combustion is presented in the first of these chapters. It is demonstrated that the UCS model is largely insensi- tive to the model PDF used, and that a β-PDF can be used successfully for both conditioning variables (mixture fraction and progress variable) in this context. The second research chapter applies UCS to a fully-premixed swirling methane flame. The results for velocity and temperature generally agree with experimental and theoretical values and a stable flame is obtained for most lean stoichiometries. When compared to experiment the flame height is greater in the UCS simulation. There are some discrepancies from the expected behaviour in the results for species concentrations and power output, which can likely be attributed to the use of the β-PDF for progress variable within a premixed context. Despite these issues, the UCS model shows promise for use across the premixed-non-premixed continuum, provided that appropriate PDF models can be identified.

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