Forced draught impact on Externally Venting Flames: an experimental and numerical investigation

Abstract

Wind can significantly influence fire development and spread in urban and forest environments causing fatal consequences for the public, the first responders, and the environment. Wind driven fires can have a significant impact on structural fires as wind can increase the fire's intensity, development, and flame spread. Buildings with flammable materials tend to be more vulnerable to wind-driven fires, as suggested by available data and evidence. In this study, medium-scale compartment–façade fire experiments were conducted using a reduced-scale ISO 9705 setup with heptane fuel and varied opening dimensions (20–40 cm) to examine Externally Venting Flames (EVF) under forced draught (FD) conditions. Using thermocouples and bi-directional probes, a systematic analysis of EVF behavior was carried out, providing key insights into flame projection and façade impact. These experimental results were then used to validate Computational Fluid Dynamics (CFD) simulations performed in FDS. A parametric study was conducted to investigate the influence of wind on EVF from fire compartments with different opening dimensions. The research is beneficial in expanding understanding of EVF development using numerical and experimental techniques to study the influence of wind velocity, ventilation conditions and opening dimensions. Predictions of EVF flow, oxygen concentration and temperature profiles were investigated and results indicate that in forced draught conditions there is less thermal impact on façade walls as the wind forces EVF outward and thus increasing the EVF projection and decreasing its height. Keywords: Externally Venting Flames (EVF); Computational Fluid Dynamics (CFD); forced draught conditions; compartment fires; wind-driven fires