Study On Smoke Spread And Control Of Underwater Tunnel Fire

Underwater tunnels are more complex than ordinary tunnel structures,with fewer entrances/exits and stronger closure.Therefore,research of tunnel fire smoke control is of great significance for tunnel fire safety.Based on the offshore horizontal section of the underwater tunnel,the key parameters of the ventilation and disaster prevention of the two major tunnels,namely the critical wind speed and the flue gas countercurrent length,was studied.Under the condition that the fire source is located in the longitudinal center of the tunnel,the smoke spread and control of underwater tunnel fire was studied by theoretically analysis and numerically simulation.The main work and results are as follows:(1)A dimensionless critical ventilation velocity calculation formula considering the length of the tunnel is proposed.The relationship between critical ventilation velocity and tunnel length is clarified by theoretical research and dimensionless analysis.It is found that the tunnel length has an impact on the critical ventilation velocity,but the rate of increase depending on the HRR of the fire.When the HRR of the fire is less than 0.15,the critical ventilation velocity in the dimensionless state increases with the tunnel length of 1/41 power growth.Otherwise(Q~*>0.15),it increases with the tunnel length of 1/25 power growth.(2)In the lateral point smoke extraction mode(with longitudinal ventilation),the numerical simulation method was used to study the influence of the height of smoke outlet,smoke exhaust volume and area of smoke outlet on the smoke spread and control.In the lateral point smoke extraction mode which has set,it is found that the smoke exhausting effect is better when the height of smoke outlet is 7m,the exhaust volume is 140m~3,and the exhaust outlet area is 3m~2.In order to facilitate the discharge and control of smoke,the smoke outlet should be as close as possible to the top of the traffic lane.And the area of the vent should be controlled as much as possible and should not be too large.At the same time,the smoke exhaust volume should be calculated and ensured to ensure safety redundancy,and if necessary,provide longitudinal airflow to enhance the control effect.(3)A dimensionless back-layering smoke length calculation formula was established.In the lateral point smoke extraction mode(with longitudinal ventilation),it was found that the downstream lateral point smoke extraction has an inhibitory effect on the upstream smoke spread(the back-layering smoke length is L)by dimensional analysis and numerical simulation:The L increases with the Q.However,it tends to be stable value exceeds 0.15(the dimensionless state).And the distance between point extraction and fire(d~*)has a similar effect on the back-layering smoke length as the Q.But the impact of d~*is less than the former.When the distance is more than 2.7(the dimensionless state),L tends to be stable.On the contrary,it is an upward trend.It also decreases when the ventilation velocity increase and the effect is extremely significant.L increases with exhaust volume.But its effect is far weaker than the ventilation velocity and the Q.Furthermore,the dimensionless correlation can correlate well with the numerical simulation.And the effect is weaker than the top concentrated smoke exhaust mode under the same conditions.