后掠机翼边界层转捩机理及控制方法研究

The swept-wing is widely used in the design of modern high subsonic transport and the decrease of the turbulent friction drag on its surface will result in the improvement of effective load capacity and flight performance. Thus, in order to reduce the soaked area by turbulent flow in the airfoil surface so as to decrease the turbulent friction drag, it is necessary to investigate the mechanism of the boundary-layer transition and explore the feasible methods of transition control on this basis. Standing on the transient growth theory of flow stability, this item studies the spatial transient growth characteristic of perturbations in the three-dimensional boundary-layer of a swept-wing and its dependence on the background noise and flow parameters, compares the flow structure and spatial evolution law of unstable perturbation wave derived by transient growth analysis and that obtained from secondary instability analysis, and reveals the crossflow instability features and the transition mechanism of the boundary-layer of swept-wings. Moreover, the optimization control of transient growth of disturbances is realized using blowing/suction method and the control mechanism of transition in the swept-wing boundary-layer is also presented, providing theoretic basis and direction guide for exploring the new control mechanism and means of crossflow instability and transition.

后掠机翼广泛应用于现代高亚音速运输机的设计当中，降低其表面湍流摩擦阻力可以达到提高有效负载和飞行性能的目的。因此为减小机翼表面湍流浸润面积从而降低湍流摩擦阻力，有必要研究其边界层转捩的机理，并在此基础上探索控制转捩的实用方法。本项目立足于流动稳定性中的瞬态增长理论，研究后掠翼三维边界层内扰动空间瞬态增长特性及其对背景噪声和流动参数的依赖关系，比较扰动瞬态增长和二次不稳定性分析所得到不稳定扰动波的流动结构及空间演化规律的差异，揭示后掠翼边界层横流不稳定性特征及其转捩机理；采用吹吸气方法实现对扰动瞬态增长的优化控制，并揭示后掠翼边界层转捩控制的机理，从而为探索横流和转捩控制的新机制、新途径提供理论依据和方向指导。

后掠机翼广泛应用于现代高亚音速运输机的设计当中，降低其表面湍流摩擦阻力可以达到提高有效负载和飞行性能的目的。因此为减小机翼表面湍流浸润面积从而降低湍流摩擦阻力，有必要研究其边界层转捩的机理，并在此基础上探索控制转捩的实用方法。本项目立足于流动稳定性中的瞬态增长理论，研究了典型后掠机翼三维边界层内最优扰动空间瞬态增长特性及其对扰动波参数、流动参数和控制参数的依赖关系，发现壁面冷却和法向吸气对于扰动瞬态增长有着良好的抑制效果，分析了它们对于最优扰动模态及其瞬态增长机制的影响规律；利用cfl3d程序对最优扰动的空间演化进行了直接数值模拟，发现最优扰动的空间能量增长与扰动瞬态增长分析的结果非常接近，证明了单频扰动波分量空间演化的非线性效应较弱，此外各扰动分量的演化方式与扰动瞬态增长的lift-up机制相吻合；搭建了低速条件下红外成像边界层转捩测量试验平台，通过对红外热图像的判读得到了来流Ma数和迎角对于边界层转捩位置的定量影响规律以及壁面法向微吸气抑制转捩发生的现象，从而为建立考虑边界层感受性的转捩预测工具、制定工程实用的转捩控制方法提供了可靠的试验数据依据和方向指导。