Sensitivity study of the effects of PDF models on the predicted structure of turbulent combustor flow

A series of numerical calculations was made of a specified, turbulent, recirculating flow in a cylindrical combustor operating with a methane-air, non-premixed diffusion flame. For all calculations, the same fuel to air mean flow ratio was used, so the overall stoichiometry of the flame was fixed. The calculations were done with three different fuel and air jet inlet velocities, and three different fuel jet turbulence levels, determined by the magnitude of the input kinetic energy profiles of the fuel jet. The flows were calculated with three ways to obtain the mean temperature, molecular weight and density distributions: without using a probability density function (pdf), with a Clipped-Gaussian pdf, and with a two-delta function pdf. The purpose of the calculations was to determined the variation between different calculated flows, with and without pdf applications, and how sensitive the computed flow field structure was to inlet velocity (Reynolds number) effects and inlet turbulence (fluctuation level) effects. The results justify the use of the computationally more expensive pdf approach (the Clipped-Gaussian) to compute such flows.