Influence of pulsating ambient wind on fire smoke in natural ventilation tunnel with unpowered ventilation cap

Unpowered ventilation cap, natural ventilation holds promise for effectively exhausting smoke during tunnel fires. However, the impact of pulsating ambient wind on tunnel fire smoke in unpowered ventilation cap natural ventilation systems remains unclear. In this paper, a 1:15 scale model of a tunnel equipped with an unpowered ventilation cap is employed to investigate the movement characteristics of smoke during tunnel fires under pulsating ambient wind. Results show that the unpowered ventilation cap significantly improves smoke exhaust and heat dissipation by reducing high-temperature zones and delaying the onset of elevated temperatures. Additionally, the unpowered ventilation cap minimizes suction-through effects, further enhancing smoke removal performance. The plug-holing height in the vertical shaft displays periodic fluctuations with changes in pulsating ambient wind. A theoretical model relating the plug-holing height to the key parameters of the pulsating ambient wind is developed and demonstrates good predictive accuracy, showing excellent agreement with experimental data. This research provides valuable insights into the use of unpowered ventilation caps in tunnel fires and fills a gap in the existing applications in such scenarios.