Example—Flowing Pool Fire

For the assumed circular shape of the spill, the fire occupies an area of 467 centered on the leak. 

The heat release rate, Q, of the fire is calculated [Equation (5-17)] as  

The view factor between the flame and target is estimated using the geometry and one of the figures 5-10 through 5-14. The flame height to pool fire radius is  

The ratios of target height to pool fire radius, Hf f jRp, and ratio of distance from center of pool fire to target edge (30.5 m) to pool fire radius, d/Rp, are likewise estimated as 0.08 and 2.5, respectively. 

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The difference between RANS and LES is depicted in Figure 20.1, which shows the temperature fields of a pool fire flame. While the RANS result shows smooth variations and looks like a laminar flame, the LES result clearly illustrates the large-scale eddies. Both results are the correct solutions of the corresponding equations. However, the time accuracy of LES is also essential for the quantitative accuracy of the buoyancy-driven flows. As Rehm and Baum have shown [10], the dynamic motions or eddies are responsible for most of the air entrainment into the fire plumes. Because these motions cannot be captured by RANS, LES is usually better suited for fire-driven flow. LES typically requires a finer spatial resolution than RANS. Examples of RANS-based fire CFD models are JASMINE, KAMELEON [11], SMARTFIRE [12], SOFIE [13], ISIS [14], and ISIS-3D [15]. Examples of LES models are the FDS [4,5] and SMAFS [16], developed at Lund University. Fire simulations using LES have also been performed by Cheung et al. [17] and Gao et al. [18],... 

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