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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%。
Under the condition of Reynolds number of 8.7 × 105, the wake and tail pressure distributions of the Ahmed car body with a dip angle of 25 ° were studied by using the visualization technology of cobra probe, pressure scanning valve and surface oil film flow. The effects of the upper edge of the tail of the tail and the baffles with different widths on the wakes and aerodynamic drag of the model are compared. It is found that there exists a pair of symmetrical tow vortices in the wake of the model, which forms a strong downward sweep near the wake centerline. The drag vortex strength is directly related to the model tail pressure distribution and the aerodynamic drag force, while the stronger drag vortices correspond to the model tail negative pressure and the aerodynamic drag force. When the width of the baffles on both sides of the bevel is 1% of the model length, not only the drag reduction effect but also the aerodynamic drag will increase by about 3.0%. When the deflector width is increased to 2% and 3% of the model length, the separation bubbles on the bevel can be significantly weakened, with corresponding drag reduction effects of 3.5% and 7.2%, respectively. The bevel edge upper edge deflector can effectively restrain the re-attachment of the separation flow on the bevel and eliminate the separation bubble on the bevel, and the effect of suppressing the eddy-vortex strength and reducing the aerodynamic drag is obviously better than that of the bevel baffle on both sides of the same width . When the width of the upper edge deflector is 1%, 2% and 3% of the model length, the drag reduction rates are 9.3%, 10.7% and 10.9% respectively.