不同扩散角下汽车风洞试验段轴向静压系数

轴向静压系数是衡量汽车风洞试验段流场品质的重要参数.收集口角度影响轴向静压系数,它的改变对不同风洞表现出不一致的变化规律.通过研究不同风洞在不同扩散角下试验段轴向静压系数的变化发现,当扩散角为1.70°时,试验段轴向静压系数不随收集口角度的变化而变化;当它小于1.70°时,收集口角度越大,试验段轴向静压系数越大;当它大于1.70°时,变化规律相反.扩散角所导致试验段轴向静压系数变化规律的深层次的原因是,射流剪切层存在固定的耗散角,当扩散角等于耗散角时,收集口角度变大导致的扩散效应与外界气流进入带来的效应相同;当扩散角小于耗散角,收集口角度变大导致扩散效应更强.这揭示了收集口角度导致静压系数变化的机理,为风洞建设确定收集口和试验段等关键尺寸提供理论和设计参考.

Axial Static Pressure Coefficients of Automotive Wind Tunnel Test Section at Different Diffuser Angles

The axial static pressure coefficient is the key parameter to estimate the flow quality of automotive wind tunnel test section. The collector angle has an influence on the axial static pressure coefficient. However, the tendency of the axial static pressure coefficient isn't the same for different wind tunnels. According to the numerical results of different wind tunnels at different diffuser angles, it is found that the axial static pressure coefficient can't be changed when the diffuser angle of 1.70°. When the diffuser angle is below 1.70°, the bigger collector angle becomes, the larger axial static pressure is. On the contrary, when the diffuser angle is above 1.70°, the law is opposite. The reason is that the constant dissipation angle exists at the shear layer. When the diffuser angle is equal to the dissipation angle, diffuser effect due to the bigger collector angle is the same as the effect due to the more flow entered from outside. If the diffuser angle is smaller than dissipation angle, the diffuser effect is more obvious. All those can be revealed the inconsistent mechanism for different wind tunnels. These findings can help to decide the key dimensions of test section and collector at the stage of wind tunnel construction.