Numerical simulation of pulsating buoyancy driven turbulent diffusion flames

Abstract

An elliptic fully coupled numerical fire model has been developed and applied to simulate the behavior of different laboratory scale pool fires. The new fire model uses the Eddy Dissipation Concept for combustion, a modified k-e model for turbulence and a modified constant fraction model for radiation. The temperature dependency of the physical properties are accounted for and the correlations involving density fluctuations are included in the present fire model. The numerical implementation of the model is such that the strong coupling between the temperature and velocity fields in the physical problem is reflected and preserved in the model. The present fire model is applicable to both 2D planar and axisymmetric fires.

The present fire model has been used to numerically simulate the pulsating behavior of a 30-cm-diameter propane fire. The unique transient results presented in the thesis clearly demonstrate the capability of the present fire model in simulating such complicated phenomena. The quantitative agreement between numerical results and experimental observation is very promising and predicted frequencies for the propane fire agree very well with the reported values in the literature.

A comparison between the predicted results and experimental data for three different laboratory scale pool fires show that the use of a constant Cp in fire calculations has a rather significant deleterious effect on the accuracy of the results and should be avoided. In addition, it is shown that the use of the standard parameters in the turbulence model produces poor results. To improve the accuracy of the results, new modifications based on an analysis of the University of Waterloo pool fire laboratory data base have been proposed and tested. The results obtained using the modified turbulence model show significant improvements compared to that of the standard turbulence model and agree very well with experimental data.