Effects of swirl on intermittency characteristics in non-premixed flames

Swirl effects on velocity, mixture fraction and temperature intermittency have been analysed for turbulent methane flames using LES. The LES solves the filtered governing equations on a structured Cartesian grid using a finite volume method, with turbulence and combustion modelling based on the localised dynamic Smagorinsky and the steady laminar flamelet models respectively. Probability density function (pdf) distributions demonstrate a Gaussian shape closer to the centreline region of the flame and a delta function at the far radial position. However, non-Gaussian pdfs are observed for velocity and mixture fraction on the centreline in a region where centre jet precession occurs. Non-Gaussian behaviour is also observed for the temperature pdfs close to the centreline region of the flame. Due to the occurrence of recirculation zones, the variation from turbulent to non turbulent flow is more rapid for the velocity than the mixture fraction and therefore indicates how rapidly turbulence affects the molecular transport in these regions of the flame.