Study on longitudinal ventilation smoke control in tunnel emergency lay-by fires under different ambient pressures

This study investigates the effectiveness of longitudinal ventilation in controlling fire-induced smoke within tunnel emergency lay-bys under varying ambient pressures through full-scale experiments and numerical simulations. The results indicate that the cross-sectional variation in emergency lay-by areas leads to energy losses in the flow field and uneven velocity distribution, which hinder smoke control. When the upper-layer smoke spreads to the edge of the lay-by and impacts the side wall, energy is dissipated. However, the resulting backflow isolates the upper-layer smoke from the surrounding air, reducing heat loss. The side wall at the edge of the emergency lay-by can block only a limited thickness of smoke. Since lower ambient pressure results in a thicker smoke layer, altitude significantly affects smoke control performance in emergency lay-by areas. Although the emergency lay-by structure is generally disadvantageous for smoke control, it is easier to contain smoke within the lay-by than to control it downstream of the fire source. A dimensionless confinement velocity model is proposed, providing a reference for smoke control system design and emergency response in highway tunnel emergency lay-bys at various altitudes.