Joint Measurements of Radial Velocity and Scalars in a Turbulent Diffusion Flame

Abstract

Simultaneous laser Doppler and Mie scattering measurements have been made in a horizontal turbulent hydrogen diffusion flame in a co-flowing stream. The nozzle fluid is seeded with aluminium oxide particles. The resulting light scattering signal is used to obtain scalar time traces which are processed together with the record of radial velocity to yield turbulent fluxes of the main species, temperature and mixture fraction. The measurement technique has been tested by experiments in a known isothermal flow. The profiles and values of normalized Favre mixture fraction fluxes are close to those of non-reacting jets only after burnout, far downstream, and it appears that chemical reaction reduces the upstream flux. The mixture fraction radial gradients and the corresponding radial fluxes show similar profiles throughout the measured region, x/D = 40 to 160, with no significant instance of counter-gradient flux. Radial pressure gradients modify the scalar fluxes significantly; estimates point to augmentation of the mixture fraction flux near the centreline, and suppression in the outer region of the flame. Gradient modelling of the mixture fraction flux for this flame yields reasonable agreement with the experimental data.