Elucidation on constant Strouhal number behind 2-D bluff bodies

为了识别二维海崖体后卡门涡街的起源，建立了一种新的方法，该方法允许在微小迎角的变化下，改变NACA 0006小翼型的对流不稳定性和绝对不稳定性。该方法是基于绝对不稳定性对翼型后缘附近分离的大小敏感的事实。在从对流到绝对不稳定的流动切换在一定的攻角，速度波动突然增长与选定的频率观察到在翼型后面的某个位置。可以得出结论，绝对不稳定区域位于该观察点附近。

To identify the origin of Karman-vortex street behind 2-D bluff bodies, a new approach was established, which allows to alter the flow dominated by absolute instability from convective instability in subtle variation of the angle of attack of a small NACA0006 airfoil. This approach is based on the fact that the absolute instability is susceptible to the magnitude of separation near the trailing edge of airfoil. In the flow switched from convective to absolute instability at a certain angle of attack, velocity fluctuations abruptly growing with a selected frequency were observed at a certain location behind the airfoil. It could be concluded that the absolutely unstable region is located near this observed point.