Study On The Characteristics Of Pollutant Diffusion Under Natural Ventilation With Single Shaft In Single Slope Tunnel

The construction of tunnels plays an important role in speeding up the development of transportation power,which improves the national highway network and promotes the coordinated and integrated development of economy.The scale of the tunnel gradually expands,but at the same time,it also causes serious problems such as pollutant diffusion.Taking advantage of the tunnel structure,study the pollutant diffusion under the natural ventilation condition of single slope tunnel with shaft,which is an important research content in the study of tunnel ventilation and smoke exhaust demonstration performance.In this dissertation,the diffusion characteristics of pollutants with a single shaft in inclined tunnel under natural ventilation mode are analyzed from the following aspects: the distribution of maximum temperature rise,pollutant distribution,heat removal efficiency and pollutant discharge efficiency,by model test and numerical simulation.The main research contents and discussions are as follows:(1)Conducting the multi-factor coupling shrinkage test of 1:30 to test temperature,reveals the single slope tunnel with a shaft of characteristic temperature distribution under the conditions of natural ventilation,this paper expounds the longitudinal arch and shaft of temperature under many factors to influence the distribution of temperature field,and verify the reliability of numerical simulation,which provides the basis for further numerical simulation analysis of pollutant diffusion.(2)CFD numerical simulation method was used to simulate pollutant diffusion characteristics under natural ventilation of single slope tunnel shaft,the results show that under different traffic conditions,the maximum temperature rise of the vault and the average temperature rise of the shaft are different with the change of the height and slope of the shaft.Based on the dimensionless analysis,the expressions of the maximum temperature rise of the vault and the average temperature rise of the shaft are obtained,as shown in formula(3-2)and(3-4).The experimental data are brought into the verification,and the errors are within 15% and 20%.(3)Adopting the CFD numerical simulation of single slope tunnel with a shaft under the condition of natural ventilation to simulate the pollutant diffusion,results show that with different traffic conditions、 the height of shaft and the change of slope longitudinal intake air speed difference,based on the dimensionless analysis,the relation expression of the dimensionless longitudinal airflow velocity is obtained,as shown in formula(4-7),comparing the simulation and prediction error is within 10%.Pollutant concentration decreases with the increase of slope and shaft height.With the improvement of vehicle operation,From blocked to normal,the total amount of pollutants in the tunnel decreases,and the analysis of the maximum pollutant concentration in the most unfavorable case,namely,the 1% slope tunnel with a shaft height of 0.2 m,meanwhile,the vehicle is blocked,which does not exceed the maximum allowable value of the specification and proves that under the corresponding tunnel size conditions and the heat source in this paper,the effect of natural ventilation is enough to meet the ventilation needs of the tunnel.(4)Using CFD numerical simulation to simulate pollutant diffusion under the natural ventilation condition of a single slope tunnel with a shaft,and make a statistic about the heat emission efficiency and sewage discharge efficiency.The results shows that when the slope is 1%,the main heat emission and sewage discharge outlet is the outlet of shaft.When the slope is 3%,the shaft mouth and tunnel outlet have synergistic effect.When the slope is 5%,the main heat and sewage outlet is the outlet of tunnel.The research conclusion of this dissertation can provide theoretical basis and data reference for vehicle exhaust emission and distribution,which also can provide for prediction and corresponding ventilation for smoke exhaust demonstration design of inclined single-shaft tunnel under natural ventilation mode.