| The tunnel as a relatively hermetic area,the ventilation system is responsible for diluting the pollutants,controlling smoke flow,providing fresh air to ensure air quality and provide favorable environmental conditions for rescue in a fire,it plays an important role in tunnel and has high research value.Most underground tunnels use variable cross-section isostatic pressure ventilation system,it is difficult to ensure the center of section at the same level in underground long tunnel,and the construction and installation are difficult.Therefore,this paper attempts to propose a equal cross-section ventilation system based on ventilation equalizers,which can be applied to transverse or semi-transverse ventilation in tunnel.CFD numerical simulation analysis method has been carried out in this paper to study the working flow-rate characteristic curve of the ventilation equalizer and the main factors(inlet velocity,air supply duct aspect ratio and number of outlets)affecting the air supply uniformity and resistance performance of the ventilation system,and which lays a theoretical foundation for the application in underground long tunnel.Numerical simulation of the air supply model with a single ventilation equalizer was carried out.The geometric model and mesh were generated by using ICEM CFD.Fluent was used to simulate the air supply.The working flow-rate characteristic curve of the ventilation equalizer was obtained.Then,the numerical simulation of the equal cross-section ventilation system based on the ventilation equalizer was carried out.The results show that the simulation model used in this paper is correct,when the inlet velocity is 9.7 m/s.the lowest and the highest outlet velocity of outlets are 4.45 m/s and 4.96 m/s.the average outlet velocity is 4.63 m/s and the maximum deviation is 7%,the standard deviation of outlet velocity is 0.16,the equal cross-section ventilation system can achieve uniform air supply.To study the influence of inlet velocity on the air supply characteristics in the system,the uniform characteristics of air supply and the resistance coefficient of the system were simulated when inlet velocity is 6.5 m/s,7.5 m/s,9.7 m/s,10.5 m/s and 12 m/s respectively.It revealed that when the angle of β each ventilation equalizer’s valve is given.The uniformity of air supply decreases slightly with the increase of the inlet velocity.When the inlet velocity is greater than 6.5 m/s,the local resistance coefficient decreases with the increase of the ventilation equalizer’s adjust angle β,and which is independent of Reynolds number.When inlet velocity increases from 6.5 m/s to 12 m/s,the power consumption per unit air volume increases from 0.18 W/(m3/h)to 0.61 W/(m3/h),and the power consumption per unit air volume increases with the increase of inlet velocity.To study the influence of air supply duct aspect ratio on the air supply characteristics in the system,the uniform characteristics of air supply and the resistance coefficient of the system were simulated,when air supply duct aspect ratio is 800:630,1250:630,1600:630,1250:1000,1600:1000 and 2000:1000 respectively.It revealed that with the increase of air supply duct aspect ratio,the standard deviation of outlet velocity fluctuates within the range of 0.22 to 0.34.So air supply duct aspect ratio have little influence on air supply uniformity.When β is given,the local resistance coefficient decreases with the increase of air supply duct aspect ratio.When air supply duct aspect ratio increases from 1.25 to 2.54,the power consumption per unit air volume decreases from 0.63 W/(m3/h)to 0.01 W/(m3/h),and the power consumption per unit air volume decreases with the increase of air supply duct aspect ratio.To study the influence of the number of outlets on the air supply characteristics in the system,the uniform characteristics of air supply and the resistance coefficient of the system were simulated,when number of outlets is 7,8,9,10,11 and 12 respectively.It revealed that when the number of outlets N=7～12 and β is given.With the decrease of the number of outlets,air supply uniformity and the local resistance coefficient also decreases.When the number of outlets increases from 7 to 12,the power consumption per unit air volume increases from 0.03 W/(m3/h)to 0.05 W/(m3/h),and the power consumption per unit air volume increases with the increase of number of outlets.To sum up,the ventilation equalizer can achieve uniform air supply in the equal cross-section ventilation system,inlet velocity and air supply duct aspect ratio have little influence on the uniform air supply in the system.So more attention should be paid to the influence of the number of outlets on the uniformity in engineering application.Inlet velocity has a significant effect on the power consumption per unit air volume,while the air supply duct aspect ratio and the number of outlets have little effect on it. |
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