Underground Interchange Ventilation Local Effect Numerical Simulation Analysis

Along with our country social economy development,the ground transportation construction is saturated,the transport infrastructure to the ground,ventilation cost is huge.Contrary to highway tunnel,underground interchange exist many fork tunnel,easy blocking effect to the air flow and vortex,loss of jet fan up pressure,cause resource waste,bad for discharge of pollutants.This paper adopt numerical simulation to straight to the hole length,diagonal branch downhill slope upward,straight up branch downhill slope,tunnel wall roughness as a variable factor,in the bus,shunt,different inlet conditions,make local loss analysis on underground interchange bifurcation tunnel,get the effect of various factors on the local damage and the general rule of bifurcation tunnel airflow,optimization of design parameters,provide reference for underground interchange ventilation system design.To local loss coefficient for the metrics,through qualitative and quantitative analysis of the simulation results,the following conclusions:(1)Flow,the Reynolds number is larger,inertia force is greater than the viscous force,produce the perpendicular to the longitudinal secondary flow,forming large eddy current,consumption of jet fan up pressure,is not conducive to cave in to air pollution emissions.Confluence of local loss coefficient,pressure loss,energy consumption is greater than the shunt.So suggest when designing underground interchange bifurcation tunnel,should try to avoid air confluence this kind of situation.(2)The feeder for uphill tunnel,local wind pressure loss in the airflow distribution,under the influence of tunnel longitudinal slope is larger;Feeder for downhill tunnels,local wind pressure loss under the condition of airflow confluence,more significantly affected by the slope.Absolute value is the same,when the confluence,a hole for partial loss is greater than the uphill downhill tunnels;Absolute value is same,shunt the branch is the partial loss of the tunnel is greater than the up/down the tunnel.So when the design,according to the points,confluence and downhill branch tunnel on the conditions of different targeted design.(3)Considering the needs of the construction process and during operation of drainage,and the influence of slope of vehicle emissions of pollutants,the suggested design bifurcation tunnel straight to the hill tunnel,slope 0.3%~2%,the biggest should not be more than 5%;Straight to the slope of down hole-4%~-2%.The diagonal branch hill slope 0.3%~2%,the biggest should not be more than 5%;Oblique downhill slope of tunnel-5%~0%.(4)When shunt,straight to the hole length L>140m,the local loss coefficient of bifurcation tunnel affected by L is small,so the design of the underground interchange bifurcation tunnel,compared with other factors,the influence factors can not consider.Confluence,local wind pressure loss is highly affected by the L,the longer the zeta loss coefficient,the greater the loss of pressure,the greater the fan up pressure loss.So when applied to the design of confluence,should try to shorten the length of the straight to the feeder.(5)The average roughness of the tunnel wall to affect the frictional resistance,the local resistance is almost no effect,so need to be considered when calculating the frictional resistance wall roughness,when calculating the local resistance of fork without consideration.