Experiments of Flapping Flags with Different Aspect Ratio in a Uniform Flow
不同展长比旗帜在均匀来流中摆动的实验研究

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.