Simulation of spherically expanding turbulent premixed flames

Abstract

Statistically spherical expanding turbulent premixed flames are computed using unsteady Reynolds-Averaged Navier-Stokes (URANS) approach. Mean reaction rate is closed using strained and unstrained flamelet models and an algebraic model. The flamelets are parametrised using the scalar dissipation rate in the strained flamelet model. It is shown that this model is able to capture the measured growth rate of methane-air turbulent flame ball, which is free of thermo-diffusive instability. The spherical flames are observed to accelerate continuously. The flame brush thickness grows in time and the role of turbulent diffusion on this growth seems secondary compared to the convection due to the fluid velocity induced by the chemical reaction. The spherical flames have larger turbulent flame speed, the leading edge displacement speed st, compared to the planar flames for a given turbulence and thermo-chemical condition. The computational results suggest st/s0 L " Rent with 0.57 # n # 0.58, where Ret is the turbulence Reynolds number and s0 L is the unstrained planar laminar flame speed, for both spherical and planar flames.