Numerical simulation of axi-symmetric fire plumes: accuracy and limitations

Abstract

Abstract The objective of this work was to determine the accuracy and limitations of a new version of Fire Dynamics Simulator (FDS), developed by McGrattan et al., on axi-symmetric fire plumes. The current version uses LES for turbulence, a mixture-fraction-based infinitely fast chemistry model for combustion, and a constant radiative loss fraction. These sub-models have been tested for unconfined fires of different sizes, based on a dimensionless heat release rate QD* in the range of 0.1 to 10.0, which covers most natural fire scenarios. No adjustment of constants or algorithms in the model FDS2.0 have been made. An examination of plume theory is made first to find the benchmark correlations. This shows a generalization for a collection of correlations based on theory, and which might be “the best”. Using the characteristic length as the scaling factor, it is found that the optimum resolution of a pool fire simulation is around 0.05. With this resolution, the flame height prediction is found to fit well with flame height correlations. Some other parameters such as temperature and mixture fraction are found to be close to the empirical estimations at flame tips. The Froude number, which describes the relative strength of momentum and buoyancy, falls within the measurement range of many researchers. The simulation also reveals that the temperature near the burner is over-predicted, while the centerline temperature and velocity in the non-combusting region is predicted well.