中文摘要：

为研究展长比对旗帜摆动特性的影响,在低速风洞内开展了质量比M＊为0.6,展长比H＊为0.2~1.5的柔性旗帜在不同来流速度下的失稳实验。利用高速摄影机和图像处理技术分析了无量纲速度U＊和展长比H＊对旗帜运动学特征（频率和振幅）的影响;利用自行研制的天平测量了旗帜受到的阻力,首次给出了旗帜的动力学特征。结果发现,保持展长比H＊不变,旗帜无量纲振幅A＊和阻力系数CD随U＊增大而增大,Strouhal数St变化很小;保持U＊不变,A＊,CD和St随H＊减小而急剧下降。同时发现,随着速度变化旗帜出现不同的振动模态。

英文摘要：

In order to study the effect of aspect ratio on flag swing characteristics,experimental investigation on swing instability phenomena at different uniform incoming flow speed of flapping flexible flags with mass ratio M＊ 0.6,aspect ratio H＊ 0.2~1.5 were conducted in a low-speed wind tunnel.High-speed digital video camera and image processing technique were used to analyze the effect of the non-dimensional velocity U＊ and the flag aspect ratio on its kinematics characteristics（flapping frequency and amplitude）.A self-designed aerodynamic balance was used to measure the drag of flags,and their dynamics characteristics were presented for the first time.Results show that for flags with given mass ratio M＊=0.6,when aspect ratio H＊ keeps unchanged,non-dimensional amplitude A＊ and drag coefficient CD increase however Strouhal number St is almost unchanged as U＊ increases;when U＊ keeps unchanged,A＊,CD and St decrease rapidly along with H＊ decreasing（H＊0.6）.It is also found that the different vibration modes of flag exist at different flow speeds.