Influence of the competitive effect of V-shaped slope tunnel on smoke characteristics

Abstract

Numerical simulations are conducted to study the influence of the heat release rate, the fire source location, and the tunnel slope on the smoke spread characteristics of V-shaped slope tunnels. Theoretical analysis and simulation results show that the smoke movement in the V-shaped slope tunnel is affected by the competition effect on both sides, which leads to the fact that the smoke only overflows from the tunnel portal closer to the fire source, and a large amount of air flows into the tunnel from the other portal. Due to the competition effect, the downstream smoke back-layering length first decreases and then increases slightly with the increasing distance between the fire source and the grade change point (refering to the intersection point of two adjacent slope lines). As the tunnel slope increases, both the back-layering length and the influence of the fire source location on the smoke spread decrease gradually. Besides, the heat release rate has little effect on the smoke movement characteristics. Based on the back-layering length and the mass flow rate distribution, the smoke movement behaviors in the V-shaped tunnel can be divided into the double-slope control zone, the transition zone, and the single-slope control zone. When the vertical distance between the fire source and the grade change point is more than 2.1 m, the smoke movement can be classified in the single-slope control zone. The mass flow rate reaches the peak value when the fire source is located in the transition zone, and the dimensionless mass flow rate is proportional to the tunnel slope and the 0.3 power of the dimensionless heat release rate.