局部柔性结构翼型激振诱发流-固界面流体能量靶向输运的机制研究

The existing experiments show that the oscillation of local flexible structure can feasibly control the flow separation and vibration and alleviate vibration of airfoil. Following our initial study, momentum transfer on the interface between fluid and structure is one of factors which lead to lift enhancement and drag reduction for airfoil, which are induced by the oscillation of wall. Therefore, the mechanism of the targeted energy transport on the oscillating interface between fluid and structure of airfoil with the local flexible structures will be studied in detail. In combination with experiment, the momentum transfer between main flow and boundary layer, which are excited by the oscillation of airfoil with local flexible structure, are studied theoretically and numerically, and stick-slip motion excited by the momentum transfer and energy transport is then studied. Moreover, some numerical methods will be developed to analyze the complex phenomena in the system studied. Further, the influences of the mechanics properties, location of local flexible structure and velocity of main flow in the boundary layer for momentum transfer and energy transport will be investigated in detail. As a conclusion, The results are significant for the study of complex dynamics in the interface between fluid and oscillating wall and can be used to develop the local flexible structure to delay the stall, alleviate vibration and enhance the lift.

实验表明在机翼前缘安置局部柔性结构，能够对机翼的流动分离进行有效地被动控制，并减缓流体激振。根据初步研究，流-固耦合振动可诱发翼型蒙皮壁面绕流中主流的动量向边界层输运，而这一动量的迁移是提高机翼增升减阻的原因之一。课题拟对机翼局部柔性结构激振诱发主流与边界层定向动量迁移机制进行深入研究。采用理论、结合数值分析及实验方法，分析翼型局部柔性弹性振动诱发边界层内流体的动量迁移和能量输运，分析该动量和能量对界面流体由无滑移产生滑移现象的驱动作用，研究柔性结构的主要力学参数、位置，以及主流速度等特性对边界层内动量迁移和能量输运的影响规律。项目的研究不仅对研究壁面流-固耦合振动引起的复杂的动力学行为具有学术意义，也对开发设计机翼的局部弹性结构的控制振动系统，实现亚音速机翼延迟静态失速、减缓气流激振，提高升力等方面具有工程应用价值。

项目针对机翼局部柔性结构激振诱发主流与边界层定向动量迁移机制等相关问题进行了深入研究，取得了一些重要的成果。首先，分别从Eulerian角度和Lagrangian角度分析了局部柔性翼型流场结构的演化特性，着重采用Lagrangian拟序结构描述了局部翼面振动对翼型表面非定常流动的物质输运/掺混及动量迁移作用；然后，针对采用气动弹性实现高效流动控制的问题，以沉浮-俯仰振荡翼型作为研究对象，采用数值方法研究了以两自由度的刚性翼型为主系统的耦合系统的自激振动。发现了此非线性耦合系统振动中存在的共振捕获特性，捕获了前、后NES与机翼振动各自由度间的靶向能量传输现象，及气动弹性中存在的频率竞争与共存问题；进一步，采用数值模拟方法研究低雷诺数下零度攻角时做沉浮振荡的二维翼型绕流。阐述了绕流尾迹中翼型运动-流动结构-非定常气动载荷间的相互影响，分析了运动壁面作用下前缘涡演化规律及尾迹结构的构成，探索出沉浮振荡翼型流动分离与前缘涡形成机制，阐释了翼型初始运动状态对偏转尾迹的影响机理；研究了流动分离和物质输运问题，揭示了流动结构演化的动力学实质。通过被动粒子的混沌散射现象，揭示了翼型沉浮振荡流动的空间多尺度特性，并根据Hausdorff理论度量了流动的分维数。最后，将局部柔性结构应用于NACA0015翼型上，对比研究了局部柔性结构安装于压力及吸力面时翼型的气动性能，并通过试验验证了局部柔性翼型所具有的性能提升能力和扩稳效果。. 项目的研究成果不仅对研究非线性气弹效应中的靶向能量传输，以及对目标系统的能量迁移等问题具有学术及应用意义。也为利用局部弹性结构的非定常激励提升翼型气动性能提供了可靠的理论依据。