A priori investigation of the constructed PDF model

The constructed probability density function (PDF) model approximates the species and temperature at a point in a general turbulent reacting flow by the species and temperature that evolved in an independent homogeneous turbulent flow. The thermo-chemical PDF is parameterized by a suitable set of lower moments, and tabulated for retrieval in 3D CFD codes. The Linear Eddy Model is used to resolve, affordably, detailed kinetic calculations in the homogeneous turbulence geometry. In this work, the constructed PDF is parameterized by the first two moments of the mixture fraction, and tested against the equilibrium, assumed-shape PDF model, which is parameterized by the same two moments. The models are evaluated by comparing mean species and temperature predictions with experimental measurements at three points in a turbulent, piloted, jet diffusion flame. The constructed PDF model exhibits consistently improved predictions, and is able to capture super-equilibrium intermediate species as well as species governed by slow kinetics, such as the pollutant NO. The advantage of the constructed PDF model is the capability to decouple the finite-rate chemistry from the multi-dimensional CFD simulation, allowing rapid CFD simulations on large meshes.