Comparison Studies of Zone and CFD Fire Simulations
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering in Fire Engineering
Comparisons between the results of zone and computational fluid dynamics (CFD) fire model simulations have been made; the zone model used was FAST (Peacock et al., 1997) and the CFD model used was SOFIE (Welch and Rubini, 1996). The underlying goal of this research is to investigate the limitations of zone models for the fire safety design of large enclosures. Three different sized fires have been simulated m two different sized enclosures: 1. A domestic-sized enclosure measuring 3.7m long x 2.5m wide x 2.5m high. 2. An industrial-sized enclosure measuring 41m long x 11m wide x 11m high. The fire sizes simulated were 330, 430, and 500kW for the domestic-sized enclosure and 300, and 600kW for the industrial-sized enclosure. The results of these simulations have been compared based on interface height and average upper layer temperature. Two definitions of interface height have been used- theN-percent method by Cooper et al. (1982) and a height derivative of temperature approach, which defines an interface at the point of maximum change in temperature with height. The comparisons between the two fire simulation techniques show that the comparisons are dependant on which definition of interface height is used; the Npercent method was not preferred because of the lack of any theoretical basis for its use, and its inability to define an interface in locations where the temperature gradient from the floor to the ceiling was small. The comparisons between the zone and CFD simulations show that for the domestic-sized enclosure, the CFD results derived average upper layer temperatures between 30 and 40% of the average upper layer temperature derived by the zone model. The CFD results indicated that the interface height was between 50 and 80% of the interface height derived by the zone model. For the industrial-sized enclosure, the CFD results derived average upper layer temperatures between 56 and 96% of the average upper layer temperature derived by the zone model. The CFD results indicated that the interface height was between 0 and 183% of the interface height derived by the zone model. Generally, the interface height predicted by the CFD model was higher than the interface height predicted by the zone model. When the enclosure boundaries are assumed to be adiabatic, zone models over-predict (compared to the CFD simulations) the average upper layer temperature for cases where the volumetric heat release rate is large.