均匀来流条件下并行排列旗帜耦合运动模式的实验

利用高速摄影技术在低速风洞中记录了不同间距并行排列的两个旗帜在不同来流速度中的耦合运动。利用自编的时间-空间演化图像处理软件分析总结了旗帜的耦合运动模式以及旗帜摆动振幅、频率和St数的变化规律。实验结果显示,随着排列间距和来流速度的变化,两旗帜可能以静止、同向摆动、反向摆动和过渡状态这四种不同的模态耦合运动。两旗帜同向摆动时摆动频率明显低于单个旗帜在相同来流中的值,反向摆动时情况相反。在过渡状态中两旗帜摆动的振幅交替增减并且运动中同时包含有两个频率,而同向和反向摆动都是单频率的运动。

Experiment of the Flapping Coupling Modes between Two Parallel Flags in a Aniform Flow

Experiment of two parallel flags in a uniform flow was conducted in a low speed wind tunnel, in which a high speed camera was used to record the kinematic of the two flags with different distances and flow speeds. Coupling modes of the flags, the flapping frequency and amplitude, and the corresponding non-dimensional frequency \%St\% were studied in terms of a self-developed space-time evolution (STE) method. Experimental results show that there are four possible coupling modes: stable, in-phase flapping, out-of-phase flapping and transitional modes for different flow speeds and distances. When the two flags flap in phase, the flapping frequency is much lower than that of a single flag in the same flow; while in the out-of-phase mode, the flapping frequency is much higher. Farther more, in the transitional mode the amplitudes of the two flags change alternately and there are two peaks of frequency in the FFT(Fast Fourier Transform) analysis, while either the in-phase or the out-of-phase modes only contains one peak value.