隧道内机动车尾气排放污染范围的数值模拟

采用商业数值软件FLUENT模拟研究隧道内轿车、卡车以及小货车在阻滞和正常行驶状态时排放尾气污染情况。考虑实际机动车尾气排放管道的大小和高度等几何参数,从横向及纵向角度考察尾气污染范围与机动车和空气之间相对速度之间的内在联系。研究结果表明:①通风风速并非越大空气质量越高,无限制增大通风风速会带来高能耗、噪声等问题,当机动车处于阻滞工况和正常行驶,相对速度分别大于8、12 m/s时,污染物扩散范围受相对速度影响可以忽略不计;②尾气横向污染范围随相对速度的增加而减小,与机动车尺寸无关,而且正常行驶的机动车横向污染范围较阻滞状态下的机动车污染范围大,两者均符合x=a/v~(1.5)+0.1的规律,其中参数a的数值与机动车行驶状态相关:当机动车处于阻滞状态时,取a=2.7;当机动车处于正常行驶状态时,取a=12.5;③污染纵向最低值随着相对速度的增加而增加,受排气管周围空气压力影响,尾气呈现出向上漂移特性;④污染纵向最高值随着相对速度的增加而先出现波峰,随后逐渐下降,其下降速率与车型有关,随着机动车尺寸的增大而减小,即轿车最大,小货车次之,卡车最小;⑤污染纵向范围整体呈现随相对速度的增加而下降的趋势,但是在相对速度处于0～5 m/s时,纵向污染范围存在最大值,对隧道通风设计时应考虑相对速度处于该范围的不利影响。

Pollution Range of Vehicle Exhaust Gas in Tunnels: A Numerical Simulation

A commercial numerical software, FLUENT, is employed to simulate exhaust pollution of cars, trucks and minivans in tunnels. Both traffic jam and normally running states are comprehensively considered in the numerical investigation. The geometrical parameters of vehicle exhaust pipes, i.e., length and height, are also taken into considered. The relationship of exhaust pollution range and relative velocity between vehicles and air is numerically studied from points of transverse and longitudinal perspectives. The research results show that: (1) Better air quality may not be achieved when ventilation wind velocity is extremely large. The unrestricted increase of ventilation velocity brings high energy consumption, noise and other issues. The influence of relative velocity on pollutant diffusion range can be ignored when relative velocities are more than 8 and 12 m/s in traffic jam and normally running states, respectively. (2) Horizontal pollution range of exhaust gas decreases as increase of relative velocity, and is independent of vehicle types. The horizontal pollution range of vehicles in normal running is larger than that of vehicles in traffic jam state, and both ranges are in accordance with x=a/v*1.5+0.1, where a is related to the driving state, i.e., a=2.7 and a=12.5 are employed in traffic jam and normal driving states, respectively. (3) The vertical minimum value of pollution increases with increase of relative velocity. There is an upward drift characteristic of exhaust gas because of air pressure around exhaust pipes. (4) The longitudinal maximum value of pollution first appears a wave peak, and then gradually declines with increase of relative velocity. The decline rate is related to vehicle type, which decreases with the increase of vehicle size, i.e., car is the largest, minivan is the second, and truck is the smallest. (5) The vertical range of pollution decreases with the increase of relative velocity. However, there is a maximum value in the longitudinal pollution range when the relative velocity is within the range of 0~5m/s. The adverse effect of the relative velocity in this range should be carefully considered during ventilation design of tunnels.