Water Spray Effects on Fire Smoke Stratification in a Symmetrical V-Shaped Tunnel

Smoke stratification in a V-shaped tunnel fire is complex due to the coupling effects of the double stack effect induced by the inclined tunnel structure, the fire thermal buoyancy, and the drag force caused by water spray system. This work investigates the influence of water spray flow rate (0 L/min to 600 L/min), atomization angle (0 degrees to 150 degrees) and distance between fire source and grade change point (0 m to 120 m) on smoke stratification in a symmetrical V-shaped tunnel through numerical simulations. The results show that the increase of water spray flow rate causes the increasing drag force which destabilizes smoke layer and contributes to the reduction of smoke layer thickness. While the water spray angle has little effect on smoke layer thickness. Through the dimensionless analysis and simulation results, a correlation for smoke layer thickness considering water spray parameters is proposed. Water spray effects on Fr describing the smoke stratification correspond to these on smoke layer thickness. That is, Fr decreases with the increase of water spray flow rate and is weak dependent on the water spray angle, and the critical Fr for turning point of the dominant effect of thermal buoyancy and drag force is linearly related to fire heat release rate. As the distance between fire source and grade change point increases, Fr changes a little on first double-slope control stage, increases on the left and decreases on the right of fire source, and eventually both levels off on second transition phase stage, thus tends to be stable on third single slope control stage.