A Web-based Introduction to Fire Modeling
Computational Fluid Dynamics (CFD) Models
A CFD model represents the cutting edge of fire protection engineering. The CFD model will apply a 3-dimensional grid of elementary control volumes to the enclosure in question. These control volumes are like that used in zone modeling, however where zone modeling might have two or three zones, a CFD model will have hundreds of thousands of control volumes.
CFD modeling then solves time dependent differential equations (known as the Navier-Stokes equations), for each control volume. This detailed approach is much more difficult and time consuming, but the Navier-Stokes equations are only constrained by the boundary surface of the problem. This allows for fewer assumptions and more complex room geometries
- Inputs:
Detailed room geometry, room construction (including all walls, floors and ceilings), number of vents (or holes) and their sizes, room furnishing characteristics, fuel/combustion characteristics, turbulence parameters, and radiation parameters - Outputs:
Smoke and heat movement/velocity, prediction of sprinkler and fire detector activation time, time to flashover, upper and lower layer temperature, smoke layer height, and species yield - Limitations:
CFD requires a large amount of computing time, as the number of control volumes increases the computational time increases
Certain parameters are assumed; CFD models must be validated before being totally trusted - Features:
CFD models can be used for complex geometry; complex geometry could be curved walls to unusually shaped buildings
CFD modeling is used extensively in other engineering fields (such as mechanical and aerospace), this means that many engineers, much more then with zone modeling, can test, develop and verify the CFD codes - Types of Models:
FDS, JASMINE, MEFE, SPLASH, UNDSAFE, STARR-CD, Fluent, CFX
