Numerical study of chemically reactive turbulent flows with radiative heat transfer

The combustion of hydrocarbon fuels produce high temperatures, rendering radiation an important mode of heat transfer in turbulent flames. The interactions between turbulence, combustion, and radiation, although acknowledged and qualitatively understood over the last several decades, are extremely difficult to model. Traditional Eulerian turbulence models are incapable of addressing the 'closure problem' for any realistic reactive flow situation, on account of the large number of unknown turbulent moments. When radiation is taken into account, the solution soon becomes numerically intractable.;A novel approach, based on the velocity-composition joint probability density function (PDF) method, has been presented. This approach is Lagrangian in nature and provides a very elegant and feasible alternative for turbulence closure. On account of its Lagrangian nature, the need to model turbulent moments, resulting from the nonlinear convective terms in classical Eulerian approaches, is eliminated. Furthermore, the reaction source terms are treated exactly (i.e., without any turbulence model). In general, all physical processes, whose description require only one-point statistics, are treated exactly because the velocity-composition joint PDF contains information about the velocity and composition fields at all time and space. Owing to this strength of the PDF method, it is possible to treat turbulence-radiation interactions by this approach.;A mixed Monte Carlo/finite-volume technique is used to solve the overall problem. The finite-volume side of the code is used to determine the mean pressure and the integrated incident radiative intensity, while the Lagrangian Monte-Carlo particle-tracing scheme is used to obtain all velocity and scalar fields.;The approach has finally been used to simulate a bluff-body-stabilized methane-air diffusion flame in a recirculating combustor. Results show the dynamic quasiperiodic behavior of the flame--a well-known, experimentally observed phenomenon in bluff-body-stabilized flames. They also demonstrate the role of radiation and turbulence-radiation interactions in altering the overall flame structure, the wall heat loads, and the overall energy emission by the flame at various Reynolds numbers and equivalence ratios. Preliminary results are presented to show the effect of arbitrary levels of soot on radiation and turbulence-radiation interactions.