Experimental Study on Control of Smoke Movement in Tunnel Fires Under Heavy Rainfall
This study investigates the effect of heavy rainfall on the smoke-movement characteristics and smoke control of tunnel fires using a reduced-scale(1∶15)experimental platform based on the Froude criterion.A series of tunnel fire tests was conducted based on four different rainfall intensities,four heat-release rates,and six longitudinal ventilation velocities.The results show that the flow field at the tunnel entrance is affected by raindrop behaviors,such as diffusion and drag,when heavy rainfall occurs.Induced airflow is directed downstream of the tunnel.When the rainfall intensity increases,the induced airflow velocity increases and smoke is restricted upstream of the tunnel.The first part of the longitudinal ventilation velocity was used to eliminate back-layering caused by the hot-smoke driving force,and the other part was used to offset the effect of induced airflow in the tunnel.The back-layering length increases with the rainfall intensity.The accuracy of the critical wind speed was verified based on a previous model.Under fire-source power levels of 3.03,6.06,9.09,and 12.12 kW,the critical ventilation velocity increased by 25.6％,17％,14％,and 9％under the effect of heavy rainfall,respectively.The higher the heat-release rate,the less affected is the critical ventilation velocity by heavy rainfall.Based on the temperature-distribution law of a tunnel ceiling subjected to heavy rainfall,the mechanism by which heavy rainfall affects smoke movement was clarified,and the effect of heavy rainfall on the key parameters for tunnel-disaster prevention and ventilation design was investigated.
tunnel engineeringcontrol of smoke movementreduced-scale experimenttunnel fireheavy rainfall
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