Vortex-induced vibration of a forced oscillating wind turbine airfoil at 90° angle of attack is numerically investigated with the aid of the dynamic mode decomposition technique. This situation may be encountered during parking or idling operations where the yaw angle is engaged due to a failure of the control system. The airfoil might induce vortex-induced vibration, which accompanies with the “lock-in” phenomenon. In this phenomenon, the shedding frequency will “jump” into the structure natural frequency that could cause limit cycle oscillations. For a series of forced oscillation calculations with constant oscillation amplitude, the airfoil will become unstable before entering the locked-in region and regain stable state before leaving the locked-in region with a frequency ratio from 0.8 to 1.2. Additionally, in this range, a smooth phase shift between the vibration-induced aerodynamic force and the airfoil motion is found, which mainly influences the characteristics of energy exchange on the airfoil surface. Finally, dynamic mode decomposition is employed to identify different flow features in the flow field to illustrate vortex-induced vibration. Dominant pressure modes are obtained, and the mechanism of energy exchange on the airfoil surface is illustrated.

中文翻译：

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基于模态分析的大迎角风力机翼型涡激振动研究

借助动态模式分解技术，对 90° 攻角下受迫振荡的风力涡轮机翼型的涡激振动进行了数值研究。在停车或怠速操作期间可能会遇到这种情况，其中由于控制系统的故障而接合偏航角。翼型可能会引起涡激振动，伴随着“锁定”现象。在这种现象中，脱落频率将“跳跃”到可能导致极限周期振荡的结构固有频率中。对于一系列具有恒定振荡幅度的强迫振荡计算，翼型在进入锁定区域之前会变得不稳定，并在离开锁定区域之前恢复稳定状态，频率比为 0.8 到 1.2。此外，在这个范围内，发现振动引起的气动力与翼型运动之间存在平滑的相移，这主要影响翼型表面的能量交换特性。最后，采用动态模式分解来识别流场中的不同流动特征，以说明涡激振动。获得了主导压力模式，并说明了翼型表面的能量交换机制。