Three Dimensional Simulations Of Fire Plume Dynamics

Abstract

The velocity and temperature fields of fire plumes are studied theoretically and computationally using the authors' large eddy simulation techniques. A version of the Navier-Stokes equations specialized to the study of fire dynamics is used as the basis for the analysis. No empirical turbulence modeling parameters are introduced into the computations. These simplifications permit high resolution solutions to the three dimensional time-dependent Navier-Stokes to be directly compared with experimental correlations of the time-averaged properties of an isolated vertical plume. Comparisons are made by averaging the time-dependent numerical results rather than the governing equations. Computed mean velocities and temperatures are shown to be in close agreement with McCaffrey's correlations. The methodology is then applied to the study of a large pool fire in an aircraft hangar with a complicated roof geometry. A simple cell masking scheme permits the inclusion of the building geometry into the calculation without sacrificing computational efficiency. The plume structure in the hangar is compared with the isolated plume properties.

A Tractable Solution for Engineering Calculations on Buoyancy Dominated Turbulent Non-Premixed Flames

“…This suggests that the location of a thin flame sheet where the peak temperature occurs, is controlled by the stoichiometry of the reactants rather than complex Kolmogorov time scale that govern premixed flames. The study of Baum [23] also confirm that in most fires, the primary momentum transport of turbulent diffusion flame is sustained by large-scale energy-containing eddies which are related to a typical geometry characteristic of a pool fire. It is found that the combustion model fails to give satisfactory predictions in upper part flame (H=10 cm).…”

Fire dynamics simulator (version 2) :

“…There are two reasons for this. First, the structure of the fire plume is so dominated by the large-scale resolvable eddies that even a constant eddy viscosity gives results almost identical to those obtained using the Smagorinsky model [11]. Second, the lack of precision in most large-scale fire test data makes it difficult to assess the relative accuracy of each model.…”

Mathematical Modelling of Pool Fire Burning Rates in a Full- Scale Ventilated Tunnel

“…The profiles of the mean temperature and the axial velocity versus radial position obtained from the cascade concept of Chen [23] and the current EDC are compared with the experimental data in Figs.4 and 5. The comparison of model predictions with experimental data allows to conclude that in most fires, the primary momentum transport of turbulent diffusion flame is sustained by large-scale energycontaining eddies [19].…”

“…In most fires, the primary momentum transport of turbulent diffusion flame is sustained by large-scale energy-containing eddies [19] which are related to a typical geometry characteristic of a pool fire. Simplicity is achieved by the recognition that reaction in pool-like fire is controlled by the diffusion of oxygen into the reactive zone in a resolved scale rather than being limited by Kolmogorov time scale.…”