PDF calculations of piloted turbulent nonpremixed flames of methane

Abstract

A velocity-composition joint pdf transport equation has been solved by the Monte Carlo method to calculate the structure of pilot-stabilized turbulent nonpremixed flames of methane. Three components of velocity and a conserved scalar, namely, mixture fraction, ξ are jointly represented in the pdf. A new model is used for turbulent frequency. Turbulent dissipation and the fluctuating pressure gradient terms are conditionally modeled. Two simple models for thermochemistry are used. In one, density is a piecewise function of ξ, and in the other, density is obtained from calculations of a laminar counterflow diffusion flame of methane with a stretch rate, a = 100 s −1. Calculations are compared with the corresponding experimental measurements performed on a number of flames ranging from flames with low mixing rates to ones close to extinction. The velocity, turbulence, and mixing fields are predicted with reasonable accuracy down to x D j ∼ 30 . The agreement with experiments is less satisfactory at x D j = 50 . This will improve with the use of better pdf models which have recently been developed [27, 30, 31]. The reactive scalars are very well predicted only for flames which are far from extinction. This is expected considering the simplicity of the thermochemical model. This paper is a first step towards implementing realistic chemistry in the code, and hence predicting the observed finite rate kinetic effects in these flames.