并列行驶的类车体气动特性数值模拟

Numerical simulation of aerodynamic characteristics of Ahmed model driving side by side

为了研究并列行驶工况下汽车的横向间距对其气动特性的影响,采用后倾角为35°的Ahmed车体模型,结合定常的Realizable k-ε湍流模型进行数值模拟研究。首先,针对单个Ahmed模型,以阻力系数为评价指标,通过与风洞实验数据比较,对数值模拟方法进行验证;然后,分析3辆车在并列行驶的情况下,其阻力系数、侧向力系数和升力系数随均匀间距变化的规律;最后,通过汽车车身表面压力和尾部流场的分布分析了气动力发生变化的原因。结果表明:相比单辆车行驶工况,在各间距下,并列行驶的类车体阻力系数均有较大的增加,其中横向间距为0.25W时,第一辆车、第二辆车和第三辆车的阻力系数分别增加22%、35%和22%;第一辆车和第三辆车的阻力系数随不同横向间距的变化趋势类似,而第二辆车的阻力系数始终大于其他2辆车;对于侧向力系数,即使未受到横向侧风的影响,由于气动干扰,第一辆车和第三辆车均受到较大的侧向力作用,而第二辆车由于流场结构的对称性,不管间距如何变化,均不受到侧向力作用。研究结果可为智能交通系统规划中对实际汽车并列行驶的气动特性分析提供工程借鉴和理论参考。

The numerical simulation is conducted with steady Realizable k-εturbulence model to study the effect of lateral spacing on the aerodynamic characteristics of vehicles under the condition of driving side by side,using the Ahmed model with a rear slant angle of 35°.Firstly,for a single Ahmed model,the numerical simulation method is verified with the drag coefficient as evaluation index through comparing with the wind tunnel experimental data.Secondly,the variation law of drag coefficient,side force coefficient and lift coefficient with uniform spacing is analyzed in the case of three vehicles driving side by side.Finally,the causes for aerodynamic changes are analyzed by the distribution of surface pressure and tail flow field.The results show that,compared with the single car driving condition,the drag coefficient of the Ahmed model driving side by side is greatly increased at each spacing.When the lateral spacing is 0.25W,the drag coefficient of the first car,the second car and the third car increases by 22%,35%and 22%,respectively.The change trend of the drag coefficient of the first car and the third car with different lateral spacing is similar,while the drag coefficient of the second car is always higher than that of the other two cars.Regarding the side force coefficient,even if it is not affected by the lateral crosswind,due to aerodynamic interference,both the first car and the second car are subjected to greater side force.However,the second car is not subjected to the side force no matter how the spacing changes because of the symmetry of the flow field structure.The results of the study can provide engineering and theoretical reference for the analysis of aerodynamic characteristics of actual cars driving side by side in intelligent transportation system planning.