Abstract: Aiming at the change of fire and wind pressure when a fire occurs in tunnels with different cross-section widths, Fluent software is used to simulate the occurrence of fire in the tunnel, and the influence of the tunnel width on the critical wind speed is analyzed, as well as the influence of the tunnel width, fire source power and ventilation speed on fire wind pressure. Research shows that when the power of the fire source is small, the tunnel with a smaller width has a larger critical wind speed; as the power of the fire source increases, the differences between the critical wind speeds decreases. About the fire wind pressure, the two factors, namely, the flow resistance around the fire zone and the increase in hot smoke friction resistance, interact with each other as the wind speed increases. As a result, the fire wind pressure will first increase as the wind speed increases, then decrease as the wind speed increases after reaching a peak value, and finally stabilize when the ventilation speed increases to the critical wind speed. With the increase of tunnel width, the influence of ventilation rate on fire wind pressure decreases gradually. The calculation formulas of tunnel fire wind pressure for different width tunnels under different ventilation rates and fire source power were established, which provided a reference for tunnel fire ventilation design.

Key words: tunnel width, longitudinal ventilation, critical velocity, fire wind pressure, Fluent