The efficiency and pollutant emission characteristics of practical combustion devices often depend critically on interactions between turbulent flow, finite-rate combustion chemistry, and thermal radiation from combustion products and soot. Due to the complex nonlinear coupling of these phenomena, modeling and/or simulation of practical combustors or even laboratory flames undergoing significant extinction and reignition or strong soot formation remain elusive. Methods based on the determination of the probability density function (PDF) of the joint thermochemical scalar variables are one of the most promising approaches for handling turbulence-chemistry-radiation interactions in flames. PDF methods have gained wide acceptance in the context of Reynolds-Averaged Navier-Stokes (RANS) approaches to predicting mean flowfields as evidenced by their availability in commercial CFD codes such as FLUENT(TM). Over the past 6 years, the development and application of the filtered mass density function (FMDF) approach in the context of large eddy simulations (LES) of turbulent flames has gained considerable ground. Some of the key issues remaining to be explored regarding the FMDF approach in LES are related to mixing model and chemical mechanism sensitivities of predicted flame statistics, especially for flames undergoing significant extinction and reignition, and application of the approach to more realistic flames, for example, those involving soot formation and luminous thermal radiation.The first term on the left-hand side is the unsteady rate of change of the PDF, the second term is convection by the mean velocity field, ... The turbulent scalar flux term is unclosed, and is modeled in FLUENT by the gradient- diffusion assumption given by a a ax i [Iau i ... The mixing model is critical because combustion occurs at the smallest molecular scales when reactants and heat diffuse together.
|Title||:||Large Eddy Simulations of Turbulence-chemistry-radiation Interactions in Diffusion Flames|
|Publisher||:||ProQuest - 2007|