A PDF APPROACH TO MODELING TURBULENCE-RADIATION INTERACTIONS IN NONLUMINOUS FLAMES

The interactions between turbulence and radiation, although acknowledged and qualitatively under-stood 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. 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 turbu-lence closure. On account of its Lagrangian nature, the need to model correlations arising 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 phys-ical 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 (TRI) by this approach. A mixed Monte Carlo / finite-volume technique has been used to simulate a bluff-body-stabilized methane-air diffusion flame in a recirculating combustor, and enables treatment of turbulence in recirculating flows, finite-rate chemistry, and multiple-band radiation calculations within the CPU limitations of a standard single-processor workstation. The finite-volume side of the code has been used to determine the mean pressure and the integrated inci-dent radiative intensity, while the Lagrangian Monte-Carlo particle-tracing scheme has been used to obtain all velocity and scalar fields. Results presented 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 heat emission by the flame at various Reynolds numbers and equivalence ratios