摘要:
在雷诺数8.7×105的条件下,运用眼镜蛇探针、压力扫描阀和表面油膜流动可视化技术对倾角为25°的Ahmed类车体尾流与尾部压力分布进行了研究。对比了模型尾部斜面上边缘和两侧不同宽度导流板对模型尾流与气动阻力的影响规律。实验发现模型尾流中存在一对对称的拖曳涡,其在尾流中心线附近形成强烈的下扫流。拖曳涡强度与模型尾部压力分布和气动阻力有直接关系,较强的拖曳涡对应的模型尾部负压以及气动阻力均较大。斜面两侧导流板宽度为1%模型长度时,不仅无减阻效果,反而会使气动阻力增加约3.0%。当导流板宽度增加为2%和3%模型长度时,能够明显削弱斜面上的分离泡,对应的减阻效果分别为3.5%和7.2%。斜面上边缘导流板可有效地抑制分离流在斜面上的再附,并消除斜面上的分离泡,其抑制拖曳涡强度和降低气动阻力的效果明显优于同等宽度的斜面两侧导流板。上边缘导流板宽度为模型长度的1%,2%和3%时,减阻率分别可达9.3%,10.7%和10.9%。
Abstract:
The near wake flow and pressure distribution on the rear end of a 25°slant angle Ahmed model were investigated at the Reynolds number of 8.7×105 ,using Cobra probe,pres-sure scanner and oil film flow visualization technique.Deflectors with different width mounted on the top edge and both side edges of the slant were tested to compare their effects on the near wake and aerodynamic drag.It is found that there is a pair of symmetrical tailing vortices in the near wake,which induces strong downwash flow near wake centerline.The strength of tailing vortices is inherently correlated with the pressure distribution on rear end and aerodynamic drag of the model.A stronger trailing vortex corresponds to larger negative pressure on the slant and also a larger aerodynamic drag.The deflectors at both sides of slant with the width of 1% model length result in about 3 .0% increase of the aerodynamic drag.With the width increases to 2% and 3%of model length,deflectors at both sides of slant can noticeably suppress the separation bubble, and result in a drag reduction of 3 .5%and 7 .2%,respectively.Deflector at the top edge prevents flow reattachment on the slant,thus eliminates the separation bubble.It suppresses the tail vor-tices and reduces the aerodynamic drag more effectively than those at the side edges.The drag re-duction rate reaches 9 .3%,1 0 .7% and 1 0 .9% for the top edge deflectors with the width of 1%, 2% and 3% of model length.
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