Experimental investigation on the characteristics of wingtip vortex at low Reynolds number
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摘要: 翼尖涡的统计特性主要包括涡核半径、平均涡量、旋涡切向速度等，其准确测量是翼尖涡控制技术得以有效实施的重要前提。采用二维粒子图像测速技术在水洞中对椭圆机翼生成的翼尖涡尾流场进行了实验观测，测量区域覆盖翼尖涡发展的近场、中远场。针对涡对不稳定运动导致旋涡统计参数失真的情况，采用涡核中心对齐平均（re-centered average）的方法，屏蔽掉涡对不稳定运动对旋涡统计参数的影响，提高了统计结果的准确度。Re-centered average统计结果表明：涡核半径和涡量峰值随流向站位分别呈现出近似符合幂函数的增长和衰减规律；旋涡不稳定运动的振幅随机翼迎角增大而减小，表明涡对抵抗扰动的能力随涡强度的增大而增强。Abstract: The characteristics of wingtip vortex mainly consist of the vortex core radius, the mean vorticity and the tangential velocity, etc., and the accurate measurements are essential for controlling the wing-tip vortex. In the present study, 2D particle image velocimetry was used to measure the velocity fields of the cross-section downstream the wake vortices in the water tunnel, and the measurement region covers the near and mid/far field where the wingtip vortex persists. Due to the effect of the unsteady motion on the accuracy of measurements, we adopted re-centered average method to extract the characteristics of the vortex pair from the velocity field, which improves the accuracy of statistical parameters. The results show that the vortex core radius and the peak vorticity increase and decrease with the stream-wise position with power law respectively; the unsteady amplitude decreases with angle of attack, which indicates that the resistance ability of the vortex pair to the disturbance grows with the vortex strength.
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Key words:
- wingtip vortex /
- unsteady motion /
- vortex core radius /
- mean vorticity /
- tangential velocity
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图 3 翼尖涡平均涡量场沿流向站位分布，α=6°
Figure 3. Variation of the mean vorticity along stream-wise position at α=6°
图 4 Temporal average和re-centered average方法统计得到的平均涡量场对比(x/b=9.5)
Figure 4. Comparison of mean vorticity obtained by temporal average and re-centered average methods at stream-wise location x/b=9.5
图 5 Temporal average和re-centered average方法统计得到的切向速度分布对比，x/b=9.5
Figure 5. Comparison of tangential velocity obtained by temporal average and re-centered average methods at stream-wise location x/b=9.5
图 6 Temporal average和re-centered average方法统计得到的涡核半径和涡量峰值对比，x/b=9.5
Figure 6. Comparison of vortex core radius and the peak vorticity obtained by temporal average and re-centered average methods at stream-wise location x/b=9.5
图 7 Temporal average和re-centered average方法统计的切向速度峰值、涡核半径和涡量峰值相对误差，x/b=9.5
Figure 7. Relative difference of the peak tangential velocity, vortex core radius and peak vorticity obtained by temporal average and re-centered average methods at stream-wise location x/b=9.5
图 8 涡核半径随流向站位的变化
Figure 8. Variation of the vortex radius with respect to the stream-wise location
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