离鳍对方背体气动特性影响的数值模拟和试验

Computational and Experimental Study on Aerodynamics of Finltes on a Square-back Body

对基于Fiat New Panda的方背体车身,首先对不同高度和长度离鳍下的整车气动特性进行研究,采用模型风洞试验测量了不同工况下的阻力系数和升力系数,同时采用Star CCM+中k-ε湍流模型进行数值仿真.研究结果表明,离鳍高度覆盖整个C柱时,可以有效地降低方背体车身的阻力系数和升力系数;离鳍使流经C柱两侧的气流分离延迟,降低尾流区的湍流强度,降低能量耗散;方背体尾流区得到更多的压力恢复,降低了前后压力差,进而降低车身阻力系数.然后采用验证过的计算方法对不同形状的离鳍进行了数值仿真,发现不同形状的离鳍均可使方背体汽车的气动性能有所提升.但不规则形状离鳍对于汽车尾部气流造成了一定影响,使得其性能表现不如普通矩形的离鳍.

Finlets with varied length and height on square- back body based on Fiat New Panda were investigated firstly both by computational and experimental ways. The scale wind tunnel tests were performed to obtain the drag coefficient and lift coefficient and the correlations with computational fluid dynamics based on k-e turbulent model were studied. It indicated that finlets along the whole C pillar could reduce both the drag coefficient and lift coefficient of a square back body. Finlets could delay air flow separation around C pillars and then decreased the turbulence kinetic energy in the wake. More pressure recovery was realized on the square back body to reduce the pressure gradient of the car body and the drag coefficient can be decreased as a result. Then the finlets with varied figures were simulated and got the results that the all the finlets can reduce the drag and lift coefficient but finlet with rectangle figure was the best.