壁面振动诱发流固界面上流体粘滞-滑移流动机制的研究

The experiments demonstrate that there exists stick-slip motion on the interface between fluid and oscillating wall of airfoil, and it is considered that the stick-slip motion is one of factors which lead to lift enhancement and drag reduction for the airfoil under oscillation, therefore, the mechanism of such stick-slip motion induced by the local oscillation of wall will studied in detail. In combination with experiments, the momentum transfer and energy transport which are induced by the local oscillating wall of airfoil will be analyzed theoretically and experimently, the mechanisim of stick-slip motion excited by the momentum transfer and energy transport is then studied, and influences of the frequencies and amplitudes of the oscillating wall on the momentum transfer and energy transport are investigated further. For the purposes mentioned above, the non-equilibrium molecular dynamics simulation is used to simulate the dynamic behaviors of fluid in the boundary layer with oscillating boundary. 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, enhance the lift and reduce the drag.

实验表明机翼局部弹性振动蒙皮与绕流耦合界面上的流体存在着粘滞-滑移（Stick-Slip）交替流动现象，初步研究认为该粘滞-滑移流动是解释翼面蒙皮小能量的局部法向振动能够增升减阻的原因之一，课题拟对壁面振动诱发流固界面上流体粘滞-滑移运动的机制进行深入研究。采用理论、数值分析结合试验研究，分析机翼局部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，研究壁面振动的幅值、频率等特性对边界层内动量迁移和能量输运的影响规律。针对以上内容，完善基于非平衡分子动力学等理论的数值模拟方法，用以模拟机翼局部振动弹性蒙皮与绕流界面上的流体微观动力学行为。项目的研究不仅对研究流-固耦合振动界面复杂的动力学行为具有学术意义，也对开发设计翼型前缘局部弹性结构的受控振动系统实现亚音速机翼延迟静态失速、产生高升力、降低阻力等方面具有工程应用价值。

项目针对壁面振动诱发流固界面上流体滑移运动的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，在现有多松弛系数Boltzmann方法(LBM)的基础上，对分子自由程进行修正，形成有效粘性，进而通过松弛系数对粒子的演化过程产生影响，实现了高Knudsen数微流动的准确模拟，捕获到宏观Navier-Stokes 方程难以描述的边界滑移现象；然后，基于非线性动力学理论，分别从Eulerian和Lagrangian角度对非定常流动分离的描述方法及动力学特性进行了理论分析。发展并将Lagrangian拟序结构（LCSs）应用于描述非定常流动分离，并通过典型的非定常流动现象解释了非定常流动分离的动力学行为，以及物质输运和交换作用在非定常流动中的重要性；最后，结合Lagrangian拟序结构，揭示了局部弹性结构诱导翼型的流动分离从固定分离向移动分离的转变，移动分离能够增强主流与附面层的物质交换与动量传递，具有定向能量输运效应，从而有效实施对流动分离的控制。研究成果对研究流-固耦合振动界面复杂的动力学行为具有学术意义，同时也对基于翼型前缘局部弹性结构实现亚音速机翼延迟静态失速、增升减阻等方面具有重要的理论指导。