机动车尾流区CO2扩散特征的数值分析

为了研究车辆运动过程中尾流区排放污染物的扩散情况,通过CFD软件FLUENT 6.1.22TM中湍流模型和组分输运方程对单辆货车尾流区内的气流速度、湍流动能和排气管排放的CO2浓度的分布进行了模拟.通过模拟结果与风洞实验的数据对比验证了模拟结果的适用性.分析了车速,排气管出口温度和湍流动能对货车尾流区内CO2扩散过程的影响,结果表明,由于出口直径和流速相对较小,排气管射流对尾流区流场的影响不明显;在排气管出口处CO2的浓度梯度最大,且随着与车尾距离的增加浓度迅速减小;尾流区内CO2在x、y、z3个方向上的浓度变化速度均随车速的增加而增加;且在尾流区内相同位置处.车速越大CO2浓度越低;排气管出口与外部环境温差对污染物扩散的影响仅局限于距离车尾0.75倍车长范围内;湍流动能最大值出现在尾流区内,有利于CO2的稀释和扩散.

Numerical analysis of exhaust gas dispersion from moving vehicles

The exhaust gas dispersion from the tailpipes of moving vehicles was studied by applying the CFD software package FLUENT 6.1.22TM. The distributions of air flow, turbulence kinetic energy and CO2 concentration in the wake behind a truck were solved by the eddy dissipation model and the species transport equation. The simulated results matched very well with the available experimental results. Analyzing the effects of vehicle speeds, temperature at the outlet of exhaust pipe and turbulence kinetic energy on CO2 dispersion showed that due to the relatively small diameter and flow rate, there was the less effect of the jet from the exhaust pipe on the air flow in the wake. Because the maximum concentration gradient existed at the outlet of the exhaust pipe, the CO2 concentration decreased with increasing distance from the rear of the truck. The horizontal and vertical concentration increased with increasing vehicle speed; higher vehicle speed induced a lower CO2 concentration at the same location in the wake. The effective scope of the temperature difference between exhaust pipe and external environment in the scope of 0.75 times the truck length. Maximum turbulence kinetic energy in the wake benefits pollutant dispersion.