Research On Controlled Circulation Ventilation Technology Of Extra-long Highway Tunnel

In recent years,the construction of highway tunnels in China has been developing rapidly.A large number of extra-long highway tunnels were constantly emerging,and the ventilation system of the tunnel became more complex.It is particularly important to study the new technology applied to the ventilation of extra-long highway tunnels.Controlled circulation ventilation is one of them.It can replace or reduce ventilation shaft,and greatly reduce the investment cost and operation energy consumption of tunnel ventilation system.Therefore,this paper has carried on the detailed study on the controlled circulating ventilation system in the extra-long highway tunnel.Firstly,the controllable circulating ventilation system was classified,and dimensionless number theoretical model for the influence on controlled circulation ventilation was deduced by using the calculation formula of diluted dust and CO required air volume.The variation law of tunnel environment comprehensive influence coefficient,ventilation load ratio and the critical diesel-gasoline ratio were analyzed.Then the key parameters of the controlled circulation ventilation were analyzed theoretically,and the formula of air dust concentration in the air exhaust vent,the supply-air outlet and the end of the short channel were derived.The critical dust concentration of air exhaust was proposed.The influence of the distributary coefficient and short-duct length on the critical smoke concentration was analyzed,the effective air quantity coefficient was proposed,the critical effective air quantity calculation formula was derived theoretically,and the influence of each parameter on critical effective air volume was discussed.Based on the theory of tunnel ventilation network,the total installed power calculation formula of vertical shaft ventilation system and controlled circulation ventilation system were given,and comparative analysis was carried out.Finally,in order to optimize the flow field structure and improve the ventilation efficiency of the system,a guide vane was set up in the arch of the tunnel downstream of the supply-air outlet.The influence of different angle and height of the guide vane on the ventilation effect of the tunnel was studied by CFD,and the optimum structure parameters of the flow guide are obtained.The results shows that:(1)Controlled circulation ventilation is suitable for tunnel with low altitude,large longitudinal slope and large proportion of diesel vehicles.(2)The air exhaust vent critical smoke concentration of is inversely proportional to the distributary coefficient and short-duct length,When the distributary coefficient is greater than 0.6,the critical smoke concentration decreases rapidly;The critical effective air quantity has a maximum value,and the extreme point magnitude decreases with the increase of short-duct length;Compared with the traditional shaft ventilation system,controllable circulation ventilation can greatly reduce the ventilation system operating energy consumption.(3)The rise pressure of the supply-air outlet is greatly improved when the angle and height of the guide vane are in the range of 2°~ 5° and 2m~ 3.5m;The supply-air outlet local resistance loss,wall friction and eddy energy loss caused by the high-speed jet can be greatly reduced by setting a optimal structure parameters guide vane.The induced length of the rise pressure effective is about 115 m,and the length is almost independent of tunnel velocity and guide vane structural parameters.