G. Cox

Mathematical modelling of buoyancy-induced smoke flow in enclosures

Abstract A computational procedure for predicting velocity and temperature distributions in enclosures containing a fire source is reported. The procedure is based on the solution, in finite-difference form, of the 2-dim. equations for the conservation of mass, momentum, energy, turbulence energy and eddy dissipation rate, with closing expressions for the turbulent viscosity and heat diffusivity. Effects of buoyancy on the turbulence model have been included. The results are shown to be in reasonable agreement with experimental data.

Field Modelling of Fire in Forced Ventilated Enclosures

Abstract This paper describes the application of the Fire Research Stations field model JASMINE to the prediction of conditions in a forced ventilated experimental fire test at the Lawrence Livermore National Laboratory. The combustion model of Magnussen and Hjertager based on eddy-break-up concepts has been used to describe the non-spreading pool fire. Comparison between measurements and predictions are shown to be in reasonable agreement and areas requiring further research indicated.

On Radiant Heat Transfer from Turbulent Flames

Abstract Turbulent flames fluctuate in temperature and emissivity. This note considers the effect that such fluctuations have on radiation heat transfer. With simplifying assumptions an expression is obtained for the intensity of radiation at a receiver which implies: (a) the instantaneous intensity at the receiver is independent of time; (b) the radiant intensity depends on the fluid dynamics of the flame; (c) a turbulent flame behaves as though it were a laminar flame of higher mean temperature.

Some Field Model Validation Studies

The three dimensional time-dependent field model known as JASMINE has been applied to several experimental fire configurations for validation purposes. Comparisons of predictions with non-spreading experimental fires conducted in a forced ventilated fire test cell (6 m x 4 m x 4,5 m), closed six-bed hospital ward (7.3 m x 7.9 m x 2.7. m) and a railway tunnel, both forced and naturally ventilated (390 m x 5 m x 4 m) are summarised in this paper. The agreement is shown to be quite satisfactory except in the immediate vicinity of the fire source. It is suggested that the model may now be used with some caution to study smoke movement problems, however, improvements to the turbulence chemistry interaction at the source will be required before the spreading fire can be reliably predicted.

Fire research in the 21st century

Abstract This annual ‘Fire Research Lecture’ was delivered on the occasion of the 50th anniversary of the Fire Research Station. Presented on 2 October 1997, it briefly traces the history of FRS from its foundation in 1947 to the current status following its privatisation in March 1997. The lecture reviews the current maturity of the disciplines of fire safety science and engineering and then provides the author’s personal view of the research requirements for the next century as driven by scientific progress and by economic and social change.

The challenge of fire modelling

Fire presents a formidable challenge to the modeller. Not only are the underlying physical processes difficult to model (turbulent buoyant convection, radiative heat transfer, combustion) but imponderables such as the location of the fire within its enclosure, the configuration of ventilation openings and the external wind conditions will all affect the outcome. A variety of models have been developed over the years and have now matured to the point at which they are enjoying increasing popularity in practical design. This paper explores the current state of art in the development of modelling, and highlights successes, areas of particular difficulty and work currently in progress to meet the challenges posed by the needs of Fire Safety Engineering.

Some Validation of Jasmine for Fires in Hospital Wards

This paper describes briefly a stage in the validation of the Fire Research Station’s mathematical field model known as JASMINE. The model simulations of fire development in a sealed six-bed hospital ward (7.33 m × 7.85 m in plan and 2.7 m in height) containing six space heaters are compared with experimental results. The temperature predictions for the prefire steady-state natural convection conditions due to the space heaters are in broad agreement with the measured data. The transient temperature predictions for the growing fire also agree reasonably well with the measurements, especially in the far field. Some discrepancies are, however, evident in the gas concentration profiles. The paper also suggests some future directions for the modelling of fire.

The Field Modelling Of Fire In An Air-supported Structure

The field modelling technique for predicting the temperature distribution and smoke movement in enclosures containing a fire source is validated against experiments carried out in a fully instrumented sports building covered by an air supported dome. The building is oval in plan and the dome has an ellipsoidal shape. A 2MW methanol pool fire located centrally on the floor of the building was used to obtain detailed measurements of temperature at a number of locations. The mathematical model simulates the transient problem in three dimensions using two different finite volume grids. The first grid is a polar cylindrical one with cells partially blocked to simulate features not coincident with grid lines. The second uses a non-orthogonal grid which follows closely the contours of the building. Results are obtained for pre-fire, fire and post-fire conditions and the two grid solutions are compared with experiments. Qualitative agreement is good throughout and trends are correctly simulated. Quantitative agreement is also good in all areas except in common with earlier studies in the immediate vicinity of the fire source. The body fitted grid solution predicts correctly the lack of stratification due to strong convection along the ceiling.

Modelling The Environmental Consequences Of Fires In Warehouses

The paper describes progress in the development of a numerical modelling methodology for predicting the environmental consequences of fires in warehouses. Two separate computational fluid dynamics models have been used to predict the emission of combustion products through warehouse roof openings and then to predict the atmospheric dispersion of the effluent. At this stage of development the dispersion model employs as boundary conditions the outflows, through the roof vents, predicted by the enclosure fire model.

Prediction of Fire Hazards Associated with Chemical warehouses

This paper describes the application of computational fluid dynamics (CFD) to the task of predicting fire product emissions from warehouses containing hazardous materials. A growing pool fire is modelled inside a warehouse with automatic, heat-detector-operated roof vents and various prescribed external wind flows. The first 5 min of the fire are simulated, by which time the heat release rate of the fire has reached 26 MW and all vents have opened. It is found that the strong thermal and entrainment processes associated with the fire are such that moderate external winds have only a second-order influence on the mass, momentum and buoyancy fluxes of the emissions. The response time of the roof vents is found to have a significant effect on the transient behaviour of the emissions. The potential and limitations for using CFD models as part of a broader environmental hazard analysis are reviewed.