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Title: Presumed and transported PDF methods applied to turbulent premixed flames
Author: Persson, Lars Magnus
ISNI:       0000 0004 2702 8345
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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The current study focuses on the modelling of turbulent premixed or partially premixed flames over a wide range of combustion regimes using various fuels. Opposed flows featuring fractal-generated turbulence are examined using different classes of models. The reacting case is in the flamelet regime of combustion and two-scalar joint β -bimodal presumed PDF and transported PDF approaches are applied for scalar statistics. In the isothermal case the k − ε model works comparatively well, in contrast to previous studies, while in the reacting case the second moment closures are outperforming the eddy viscosity based closures. The transported PDF approach indicates an under-prediction of the turbulent burning velocity in this flow. The latter approach is therefore applied to compute freely propagating turbulent premixed flames using comprehensive chemistry. Turbulent burning velocities are extracted and compared with experimental data. The computed cases are covering the laminar flamelet to the distributed reaction zone regime. The mixture reactivity is also varied through different fuel/air mixtures and explored in terms of the Zeldovich number. The fuel/air composition studied include fuel-lean CH4, stoichiometric CH4 and C2H6 and fuel-rich H2 mixtures. The impact of molecular transport is investigated through the inclusion of an explicit analytical formulation. A multi-scale scalar dissipation rate closure that accounts for the influence of the Da number is extended in a simple manner to include Le number effects. An industrial swirl-stabilised partially premixed fuel-rich CH4 flame is simulated at realistic gas turbine conditions using the node-based Eulerian transported PDF approach coupled with a second moment closure for the velocity field. The case is in the well stirred reactor regime and the chemical kinetics is modelled using a global reaction scheme for hydrocarbon combustion. The flow field is initialised and compared with the predictions of the two-scalar joint β-bimodal presumed PDF approach.
Supervisor: Lindstedt, Peter ; Milosavljevic, Vladimir Sponsor: Siemens Industrial Turbo-machinery AB
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral