MODELING FIRE BEHAVIOR IN AN ENCLOSURE WITH A CEILING VENT

The flow initiated by a heat source inside an enclosure with a ceiling vent is considered. The problem is formulated computationally in primitive variables and includes compressibility and buoyancy effects; combustion and radiation are ignored. Predictions are obtained by using a field model in a space of 0.45 m x 0.45 m divided into 40 x 40 uniform grids; an additional 8 x 4 grids are employed to represent the vent. A mixing ratio lambda (defined mathematically as T(mix) = lambda x ambient temperature + (1 - lambda) x vent discharge temperature) is introduced to compute the temperature of the incoming stream at the vent. For lambda between 0.3 and 0.5, the mean flow field and interior temperatures show satisfactory comparisons with experimental data. However, the predicted vent temperatures exhibit large fluctuations, which bound the experimental values; the discrepancies may be attributed to the slow frequency response of the thermocouples and numerical oscillations. The results generally show that, for this configuration, the flow field is bistable and vortical inside the enclosure, with an irregular pulsating vent discharge of the order of 0.5 Hz; the interior temperature distribution is essentially uniform.