Study On The Smoke Flow Characteristics Of Immersed Tunnel With Central Exhaust System

The low cost,high quality,short duration and so on make the Immersed tunneling method become the main method of constructing the tunnel underwater.Immersed tunnel’s longitudinal slope is often V-shaped,and the slope section is longer,and the smoke in the tunnel fire is often longer and has greater damage to the tunnel structure and electromechanical facilities.The use of a central exhaust smoke exhaust system as a fire tunnel exhaust system can harvest a good effect,reduce the loss caused by the tunnel fire.In this paper,immersed tunnel smoke exhaust system is designed based on the summary of domestic and international smoke exhaust patterns.And research on the smoke flow characteristics of the central exhaust system in the immersed tunnel based on the numerical simulation and the theoretical study.The methods and characteristics of the commonly used tunnel fire smoke exhaust method at domestic and abroad is summarized,and the detail the characteristics of central smoke exhaust system is introduced.Combined with the characteristics of the immersed tunnel,the immersed tunnel under the fire occurred in different locations of the central smoke exhaust system is designed.According to the previous research results,the calculation formula of the flow velocity distribution of the exhaust smoke vale and the smoke flow distance are established by using the energy conservation method of the smoke flow control body.Dividing the tunnel into the exhaust valve opening section and the exhaust valve closing section,and the energy equation is established to obtain the temperature field under different sections.And then the smoke flow rate distribution along the tunnel is established by the Bernoulli equation,and also the formula of the designed immersed tunnel is given.The pressure field and the wind speed field of the fire zone were simulated by FDS,and the decrease of the pressure and the increase of the longitudinal wind speed were studied in different heat release rates and different longitudinal wind speeds.The temperature field,the smoke flow velocity and the flue gas distance of the smoke flow under the immersed tunnel are simulated using the FDS.The characteristics of smoke flow in the case of the change of the longitudinal wind speed,the change of the tunnel slope and the opening range of the smoke exhaust valve are studied respectively.Using the theoretical calculation results as a comparative analysis,and the reasonable way of the immersed tunnel smoke exhausting is discussed according to the research.