Numerical Simulation And Experimental Study On The Effect Of Cross Channel In Highway Complementary Ventilation

With the rapid development of China’s transport industry,the number and length of highway tunnels which have completed are increasing,China has become the country that it has the largest,the most complex and fastest growing tunnels in the world.Meanwhile,with the high cost of tunnel operations,maintenance and the increasing tunnel accidents,more and more experts have become paying attention to tunnel ventilation at home and abroad.The study shows that the cost of mechanical ventilation in highway tunnels is proportional to the cubic power of the tunnel length,so it is very important to choose the appropriate tunnel ventilation method.Due to the factors such as geology and geomorphology when the highway tunnel is built,the road tunnel often has a certain slope,the difference of the pollutant concentration when the vehicle is running downhill causes the difference of the air volume in the double tunnel.In view of this situation,domestic and foreign experts began to put forward the air exchange ventilation theory gradually apply to the newly built two-hole one-way road tunnel.Based on the research status of the complementary ventilation system at home and abroad,this paper mainly studies the following aspects of relying on a tunnel in Xiamen,Fujian Province.In the aspect of theoretical calculation,this paper obtains the scheme of ventilation design of the tunnel by calculating the forecast of the long-term traffic and the calculation of the air demand,and proves the applicability of the complementary ventilation system in the ventilation of the highway tunnel.The research shows that: In the long-term,controlling the right line tunnel driving speed of 60 ~ 80 km / h,left line driving speed of 100 km / h,relying solely on natural wind and vehicle traffic with a complementary ventilation network can meet the normal conditions of the tunnel the operational ventilation requirements.In the physical model test,based on the similarity theory,the velocity field of the section at different locations under normal working conditions and the flue gas concentration field under fire conditions were tested by setting the jet wind turbine at the tunnel mouth to simulate the traffic wind of the vehicle.The distribution of flue gas concentration field in the tunnel fire condition is tested by the oil tank combustion test in the model tunnel.The results of the model test and the causes of the error are analyzed and explained.It proves that using CFD numerical simulation method in tunnel ventilation research is feasible.In the aspect of numerical simulation,the three-dimensional numerical model of highway tunnel ventilation was established by using FLUENT numerical simulation software.The influence of the number of transverse channels on the air velocity in the tunnel is simulated.Meanwhile,the "point source" model was set up based on vehicle emission pollutants and the distribution of pollutants in the tunnel was simulated with CO concentration as a reference.Through the establishment of the fire combustion model,the heat release rate of the fixed fire was set under the fire conditions.The influence of the horizontal channel opening and closing conditions on the flue gas concentration field and the temperature field distribution was studied.Through the analysis of the simulation results,the following conclusions are drawn:1)Under normal operating conditions,the number of cross-channel is not the better,the additional horizontal channel has no obvious change to the gas flow rate in the tunnel,and the ventilation effect of the complementary ventilation system is not obvious.At the same time,due to the middle of the additional cross-channel internal air flow speed is too slow and lead to the problem of high CO concentration is not conducive to cross-channel personnel and vehicle activities.2)The opening and closing of the cross channel under the fire condition has obvious influence on the flue gas concentration field and the temperature field in the tunnel.When the transverse channel is opened,the piston wind of the left tunnel is entering the right channel through the cross channel,increasing the rate of flue gas diffusion and reducing the percentage of flue gas concentration in the tunnel.Besides,after the opening of the cross channel,the temperature within the scope of personnel activities is obviously reduced,and the temperature near the fire source is stable below 400 K.Comprehensive consideration,keeping the opening of the cross channel can enhance the chance of escape greatly and contribute to the development of fire fighting and rescue work when a fire occurs in the tunnel.