Turbulent Diffusion Flames with Large Buoyancy Effects

Abstract

In order to contribute to the modelling of room fires, experimental results are presented concerning turbulent diffusion flames obtained with a 30 cm diameter burner and corresponding to initial Froude number F in the range 2 × 10^–6 < F < 1.2 × 10^–5, and calorific powers Q in the range 16 kW < Q < 38 kW. The results concern main species mole fractions, temperature and flow velocity. The spectral analysis of the signal obtained by laser velocimetry shows that the flow is periodic or quasi-periodic in the lower part of the flame, where the quasi-totality of the combustion is achieved. Although the k-ε-g models imply a fully turbulent flow, the comparison of our experimental results with predictions based on the models developed by F. Tamanini shows that the Wallburn model gives a satisfactory approximation of the mean velocity distribution along the flame axis. However these models underestimate the lateral expansion of the flame.