Influence of Buoyancy on Turbulent Hydrogen/Air Diffusion Flames

Abstract

A model which treats the axisymmetric turbulent mixing of co-flowing streams, including non-equilibrium chemistry, is applied to the prediction of buoyant H₂/air diffusion flame properties. The model, which employs the Donaldson/Gray eddy viscosity formulation, is first tested against the nonbuoyant laboratory H₂/air flame data of Kent and Bilger. It is shown that centerline temperatures and species mole fractions can be predicted to good accuracy. However, the calculated rate of radial transport of energy and mass is greater than that measured in the laboratory experiments. The results of a series of parametric calculations on buoyant flames and comparisons with buoyant flame length data show that: (1) flame properties scale with nondimensional distance for Froude numbers (Fr) greater than about 10⁶, (2) buoyancy significantly affects temperature decay rates downstream of the location of maximum temperature (after all the H₂ has burned), and (3) the predicted influence of Fr on buoyant flame lengths is consistent with the available data.