Performance optimisation and predictive modeling of smoke control in asymmetrical V-shaped tunnels: Synergistic effects of air curtains and side-wall extraction on temperature and smoke propagation

Controlling smoke propagation in asymmetrical V-shaped tunnels remains a formidable challenge, particularly at slope transitions where buoyancy-driven stack effects often compromise traditional ventilation strategies. This study proposes and optimizes a synergistic smoke control system that integrates side-wall extraction with an active air curtain barrier. Using Fire Dynamics Simulator (FDS), a comprehensive parametric analysis was conducted under varying fire loads (5–15 MW) and geometric configurations, specifically targeting the critical scenario of a 1% fire-side and 3% non-fire-side gradient. The results demonstrate that the proposed system significantly outperforms standalone extraction, effectively confining smoke to the fire source side and reducing peak ceiling temperatures. Through sensitivity analysis, jet velocity and injection angle were identified as the dominant control parameters, with an optimized configuration (2 m/s at 15°) achieving maximum confinement efficiency. Crucially, based on dimensionless analysis, predictive correlations are proposed for the ceiling-level temperature rise as functions of the lateral extraction velocity and air-curtain parameters, showing good agreement with simulations. These predictive models provide a robust theoretical tool for fire safety engineering, offering practical guidance for designing resilient smoke control systems in complex V-shaped underground infrastructures. Practical application This study provides building services engineers and fire safety consultants with a validated smoke control strategy for complex asymmetrical V-shaped tunnels. By integrating side-wall extraction with optimized air curtains, professionals can effectively prevent smoke backlayering at critical slope transitions. The research defines optimal design parameters—specifically identifying jet velocity and angle as primary control factors—offering a more space-efficient and cost-effective alternative to traditional oversized longitudinal ventilation. The proposed dimensionless correlations serve as a direct technical reference for sizing extraction systems, ensuring enhanced life safety and structural protection in modern underground infrastructure design.