Presumed subfilter PDF model for finite-rate oxidation of soot in turbulent reacting flows

Modeling soot evolution in turbulent reacting flows using Large Eddy Simulation is challenging due to the complex subfilter soot-turbulence-chemistry interactions. Soot particles form at fuel-rich mixtures and are subsequently oxidized as they are transported toward fuel-lean mixtures. In previous work, this phenomenology was explicitly encoded into a presumed subfilter PDF model for soot by confining soot to subfilter mixtures where growth rates exceed oxidation rates. However, this model implicitly assumed that oxidation is infinitely fast. In this work, a new presumed subfilter PDF model for soot is proposed that accounts for finite rate soot oxidation. The distribution of soot with respect to the flame structure (mixture fraction) is determined by comparing the local relative motion of diffusionless soot particles with respect to the flow with the local oxidation rate. When the oxidation rate is suppressed or the transport rate very fast, soot is allowed to penetrate further into fuel-lean mixtures. The new model is validated a priori against DNS databases of turbulent nonpremixed jet flames and then a posteriori against experimental measurements in a laboratory-scale turbulent jet flame.