Buoyant axisymmetric turbulent diffusion flames in still air

Abstract

A theoretical and experimental study of buoyant, axisymmetric, turbulent, diffusion flames is described. Measurements included profiles of mean velocity, velocity fluctuations, Reynolds stress, mean temperature, and mean concentrations for two flames having heat release rates of 1.67 and 8.51 kW, respectively. Flame shape and the variation of flame radiation along the axis were also measured. A portion of the measurements were compared with a k- ϵ- g turbulence model which was developed earlier and has been calibrated for a variety of combusting and noncombusting forced flows at relatively high Reynolds numbers. The model provides for buoyancy in the governing equations for mean quantities, but neglects effects of buoyancy on turbulence characteristics. The model provided an estimation of data trends; however, errors in the predictions were greater than for forced combusting flows. The greatest discrepancy involved the width of the flow in the upper portions of the flames, which the model underestimated by as much as 50%. Although care was taken to minimize room disturbances during the tests, it is felt that they may be an important factor in the discrepancy. Effects of low Reynolds numbers and buoyancy on turbulence properties, uncertainties in estimating the initial conditions for the computations, and the accuracy of the measurements are also advanced as factors contributing to the differences between predictions and measuremnets.