Evaluating fire risk in double-skin green façades under external wind conditions: A sustainable high-rise design

Double-skin green facades, as novel sustainable building envelopes, are gaining widespread adoption. However, the coupled mechanisms governing their fire behavior remain poorly understood, particularly the interaction between external wind and fire development within the DSGF cavity. This lack of systematic research introduces uncertainties in modeling and risk assessment. This study employs a mechanism-oriented multiscale approach, integrating laboratory-scale experiments, validated computational fluid dynamics simulations, and full-scale numerical modeling to investigate wind-fire coupling within the cavity. Within the studied structure, a distinct non-monotonic response of fire to wind was observed. At low wind speeds (approximately 0.5 m/s), wind enhances flame adhesion and ventilation, resulting in a significant increase in the peak heat release rate. As wind speed increases within the range of 1.1 to 2.0 m/s, fire behavior transitions from wind-enhanced to wind-suppressed. This shift manifests as flame instability and altered flow direction within the cavity. When wind speeds approach 2.0 m/s, the flame propagation pattern reverses markedly and the peak heat release rate decreases significantly. Simulations of enlarged cavity dimensions indicate that the onset of this transition varies with geometry, confirming that the reported wind speed values are structure-dependent rather than universally applicable critical thresholds. Full-scale simulations also successfully reproduced the non-monotonic trends observed at smaller scales. The research findings mechanistically elucidate the behavior of facade fires under wind conditions and underscore the necessity for scenario-based fire safety assessments that explicitly account for local wind conditions and facade geometry.