Steel Buildings in Europe

Part 7: Fire Engineering 7 - 49 A7 12.5m*9m A13 25m*54m A3 12.5m*9m A4 12.5m*9m A8 12.5m*9m A2 25m*18m A1 25m*18m A12 25m*18m A9 12.5m*9m A14 25m*54m A10 12.5m*9m A5 12.5m*9m A6 12.5m*9m A11 25m*18m Fire source Figure 6.2 Example of fire modelling using zone models for an industrial building 6.1.2 Field models Field models (computational fluid dynamics models) are the most sophisticated deterministic models for simulating enclosure fires. They incorporate sub- models for turbulence, heat transfer and combustion. The CFD modelling technique is based on a complete, time-dependent, three- dimensional solution of the fundamental conservation laws (conservation of mass, momentum, and energy). The volume under consideration, usually a fire compartment, is divided into a very large number (sometimes hundreds of thousands or even millions) of cells. The approximate number of cells appropriate for the studied compartment will depend on the compartment geometry, the accuracy required, and from a practical standpoint, the computer speed and memory. Three cases of field models, according to the turbulence method implemented in model, exist:  Direct numerical simulations (DNS): The basic equations are directly solved but need very short time and spatial steps in order to simulate all time and spatial scales coming from the turbulent and the chemical processes. DNS require particularly powerful computers and are used for academic studies or are confined to simple applications.  Large Eddy Simulation (LES): Large scale motions of the flow are calculated while the effect of smaller scales is modelled using sub-grid scale model. The most commonly used sub-grid model is the Smazorinsky model.