基于流动显示的翼尖涡不稳定频率测量

Frequency measurement of wing-tip vortex instability by flow visualization

翼尖涡涡核振荡频率的准确测量是翼尖涡控制技术得以有效实施的重要前提。采用流动显示方法,研究了椭圆机翼翼尖涡在低雷诺数条件下的不稳定特性。分别采用单点谱分析和动力学模态分解技术,从流动显示图像序列中提取了涡核振荡的短波不稳定模态的频率,2种方法得到的频率相对误差最大不超过5%。研究结果表明:涡对的空间运动通常展现出长波与短波模态的耦合,涡核的高频短波振荡耦合在低频长波摆动中,以前者为主要含能模态;短波不稳定性的无量纲振荡频率随雷诺数的增大而增大、随机翼攻角的增大而减小。

The accurate measurement of the dominant frequency of wing-tip vortex core oscillation is essential for controlling the wing-tip vortex. In the present study,the instability of wing-tip vortex,which is generated from an elliptical wing,was investigated under low Reynolds number via flow visualization technique. Point-wise spectrum method and dynamic mode decomposition were applied to extract the dominant frequency of the short-wave instability of the wing-tip vortex core from the flow visualization image sequence,and the maximum relative error of these two methods is less than 5%. The results show that short-and longwave instability modes are developed simultaneously among the vortex pair; the high-frequency vortex core oscillation is coupled with the slow side-to-side movement of vortex tube,and the former is the main energy mode; the non-dimensional frequency of the short-wave instability increases with the increase of Reynolds number,and decreases with the angle of attack increasing.