Intermittency and Conditional Velocities in Premixed Conical Turbulent Flames

Abstract

A turbulent premixed ethylene/air conical flame in a large Bunsen type burner has been studied using a two-component laser Doppler anemometry (LDA) system. Conditioned reactant velocity statistics were measured using a silicon oil aerosol, which evaporated and burned through the flame fronts, as the LDA seed. The intermittency was also determined by monitoring the Mie scattering intensity from the aerosol. The unconditioned velocity statistics were measured using aluminum oxide particles. A conditional analysis method was developed to deduce the conditioned product velocities. The method is based on deconvolution of the velocity probability density function (pdf). The difference between the conditioned mean product velocity and the conditioned mean reactant velocity, ..delta..U, within the oblique region of the Bunsen flame is less than that observed previously in v-shaped premixed turbulent flames. The main reason is that combustion induced flow acceleration is lower for the lean test mixture. The conditioned product rms velocities are almost equal to the conditioned reactant rms velocities meaning that flame generated turbulence is not significant. The unconditioned and conditioned covariance (Reynolds stress) are negligibly small through the flame. Since the flame brush is almost parallel to the burner axis, this result is consistent with the covariances for themore » v-flames after the data was transformed with respect to the flame co-ordinate. 26 refs., 9 figs.« less