带主动襟翼的垂荡翼的模态竞争：多尺度模态分析方法
Mode Competition in a Plunging Foil with an Active Flap: A Multi-Scale Modal Analysis Approach
摘要：
流致颤振在飞机稳定性、可再生能源提取、动物运动以及许多其他应用中具有重要作用。虽然颤振是一种普遍存在的现象，但颤振响应的控制主要局限于简化系统，并且通常借助于线性无粘流理论。在本文中，我们数值研究了如何使用主动襟翼调节翼片的俯冲响应，以提高结构安全性或提高翼片的能量提取效率，并采用紧耦合流固耦合算法。广泛的翼型和襟翼设置进行了测试，并研究了它们的流动动力学。一种新的适用于流固耦合系统的多尺度模态分析技术成功地分离了主动襟翼诱导模态和流动诱导模态。据观察，这两种模式之间的竞争决定了箔的暴跌响应。主动襟翼可以通过较大的拍动振幅来调节前缘涡的脱落，从而调节翼型的垂荡运动。提出了用竞争模态能量之比来评价变形曲面的控制效果，并将该比值趋近于1与锁定的发生相关联。结果表明，变形襟翼是一个很好的候选人主动流动控制。
英文摘要：
The flow-induced flutter has a significant role in aircraft stability, renewable energy extraction, animal locomotion, among many other applications. While being a ubiquitous phenomenon, the control of the flutter response has been primarily limited to simplified systems and, often, with the help of linear inviscid flow theories. In this paper, we numerically investigate how the plunging response of a foil can be regulated using an active flap to improve structural safety or enhance the energy extraction efficiency of the foil with a tightly coupled fluid-structure interaction algorithm. A broad range of foil and flap settings was tested and their flow dynamics have been investigated. A novel multi-scale modal analysis technique suitable for fluid-structure interaction systems successfully isolates the active flap-induced and the flow-induced modes. It is observed that the competition between these two modes dictates the plunging response of the foil. The active flap can modulate the leading edge vortex shedding with larger flapping amplitude and regulate the foil heaving motion. The ratio of the competing modal energy is proposed to evaluate the control efficacy of the morphing surface, and the onset of the lock-in is associated with the ratio approaching unity. It is shown that the morphing flap is a good candidate for active flow control.
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