Abstract: To clarify the relationship between longitudinal wind speed and smoke exhaust wind speed under the new one-way large-spacing point-type coordinated smoke exhaust mode in tunnels, this paper defines the safe distance of smoke spread, and discusses the effects of longitudinal wind speed and smoke exhaust wind speed on smoke spread distance under the new smoke exhaust mode. Combined with numerical simulation and scaled-down model tests, the relational expression of smoke exhaust wind speed and longitudinal wind speed satisfying the safe distance of smoke spread is derived, and the correlation between smoke spread distance and the Froude number (Fr) is obtained. The results of the combined analysis of the upstream smoke counterflow length Lup ≤ 30 m and the downstream smoke overflow length Ldown ≤ 4H show that, Lup decreases with the increase of longitudinal wind speed, while the influence law on Ldown is not obvious; the variation of Lup with smoke exhaust wind speed is not significant, whereas Ldown decreases gradually with the increase of smoke exhaust wind speed. When Fr≤0.45 at 30 m upstream of the fire source and Fr≤1.5 at 4H downstream of the smoke vent, the smoke spread is within the safe distance; the dimensionless smoke exhaust wind speed has an exponential relationship with the dimensionless longitudinal wind speed. The scaled-down model tests fully verify the reliability of the numerical simulation and the dimensionless relational expressions.

Key words: tunnel, longitudinal wind speed, smoke exhaust wind speed, numerical simulation, backflow length, overflow length