Numerical and Theoretical Evaluations of a Full-Scale Compartment Fire with an Externally Venting Flame

International audienceUnderstanding of the physics and mechanisms of externally venting flames from enclosure fires with parallel sidewalls at the opening is fundamental to investigating fire spread of U-shape building façade. This work aims to identify the impact of separation distance of sidewalls on façade flame height, heat flux and sustained internal combustion. A series of numerical simulations is conducted in a full-scale compartment with 3.6 m in length/width and 3.1 m in height. An external façade wall is measured 6 m in height and 3.6 m in width. A pyrolysis surface with an area of 3.2 × 3.2 m2 is placed in the middle of the enclosure with a theoretical heat lease rate varying from 1 to 8 MW. The semi-empirical correlations, derived from a reduced cubic enclosure, are evaluated for a full scale façade fire for identifying the flame height dependence on the separation distance of sidewalls. It is found that an enhanced buoyancy-induced flow between sidewalls leads to an increase of the flame height by a factor of 50% and a rise of the peak of radiation heat flux by a factor of 20% as compared to a flat façade fire. The height of externally venting flame is sensitively reduced by a factor of 40% to 50% with an increase of the normalized sidewalls distance by opening width up to 3. The predicted flame height is more pronounced with an increase of flame height by a factor of 40% for a full scale façade than for a small scale one due to turbulence development. The predicted internal HRR is in quantitative agreement with the one from the correlation for a global equivalence ratio below 3. The predicted temperatures are in good agreement with the experimental data except in the intermittent-like regions where an over-prediction of the temperature by a factor of 50% is found due to a reduction in accuracy of LES combustion model