【作者】 郭秋亭；

【导师】 张来平； 赫新；

【作者基本信息】 中国空气动力研究与发展中心 ， 飞行器设计， 2009， 硕士

【摘要】 昆虫和鸟类的飞行性能极为高超,其飞行过程给予我们很多的启示。根据生物仿生学的原理,同时借助于空气动力学技术的发展,各种新型的变形飞行器应运而生。如今,高强度固定翼飞行器均对特定的飞行条件进行了优化设计,但在非设计状态往往难以达到较高的飞行效率。结构设计的困难、气动弹性的不稳定性、机翼蒙皮材料的性能都限制了飞行器的飞行包线进一步扩大,为此科研工作者提出了机翼形状控制[1](wing shape control)的概念。例如,洛克希德·马丁公司提出的折叠翼无人战斗飞行器(UCAV),具有长时间的巡航能力,能够通过折叠机翼快速进入俯冲和战斗状态,战斗结束后又可转换为长时间的巡航状态。这种构型有两处可以折叠,能够提供内翼折叠130度、最多200%的翼面积变形。变形使得巡航/侦察的功效和俯冲/突防能力集于一体,相比于常规作战平台显著提高了作战能力。本文的目的就是希望建立一套较为完善的柔性变形体数值模拟方法,数值模拟变形飞机机翼折叠/展开过程的非定常流动,研究在机翼变形过程中变形飞机的动态气动特性。变形飞机机翼的折叠/展开运动是一个强非定常、非线性过程,其计算网格必须随机翼的运动而发生大变形。因此对变形飞机流场的数值模拟,需要建立合适的动态网格生成方法,并建立高效的可压缩流非定常计算方法。由此,本文设计了如下的组织结构:在第一章的引言中,介绍了关于飞行器的多种变形方案以及国内外研究进展,对混合网格生成方法、动态网格生成方法和非定常数值计算方法做了简要的回顾,最后介绍了本文的工作。第二章重点介绍了静态/动态混合网格生成方法,包含了动态混合网格生成的整体方案,静态混合网格生成方法,Delaunay背景网格生成方法,以及基于Delaunay背景网格插值法的局部网格重构等问题,并给出了本文数值计算所采用的动态混合网格的生成实例。第三章介绍了基于上述动态混合网格的非定常计算方法,包括流动控制方程,空间和时间离散方法,动网格计算的几何守恒率,边界条件的处理等。在章节末尾给出了定常数值验证结果和典型非定常数值验证结果,计算结果与文献数据的吻合证明了本文采用的计算方法有较高的计算精度和计算效率。第四章研究了局部翼面主动变形对跨声速翼型气动特性的影响,试图根据“流动滚轴效应”的思想,通过物面的动态变形,改变跨声速条件下主导翼型升力系数的上翼面激波出现的位置,从而提高翼型升力系数。为此,我们将局部行波壁模型和局部主动振动模型加载至NACA0012翼型和超临界翼型RAE2822上,考察了不同参数的计算状态。计算结果表明,局部主动变形模型带来的翼面局部变形在大部分情况下导致上翼面激波前移,从而降低了翼型的升力系数。由此表明,局部主动振动模型应用于跨声速条件下后移激波的方法是不成功的。第五章研究局部翼面主动变形对低速翼型气动特性的影响,探讨了在低速多段翼型30P30N的主翼段上表面加载局部主动变形模型后翼型的气动特性,主要关注升力特性的影响,包括局部左行波壁模型、右行波壁模型、左行合成波壁模型、右行合成波壁模型和局部主动振动模型对翼型升力特性的影响。对于翼型在失速状态下加入前述5个变形模型,翼型都有不同程度的增升作用。本章讨论的各种局部主动变形模型应用于翼型的失速控制对三维机翼的失速控制有一定的参考价值。第六章进行了折叠翼变形飞机动态气动特性及非定常流动机理的初步研究,本章首先参考文献资料设计了简化的折叠翼变形飞机模型,然后利用前述方法生成了非结构动态网格,最后利用第三章的非定常数值计算方法进行了无粘流数值模拟。数值计算结果表明,变形飞机机翼在折叠/展开过程中,飞机的升力特性变化较大,上翼面的激波位置在机翼折叠/展开过程中均会发生前移,从而降低了升力系数。最后,在结束语中,对现有工作进行了总结,指出了存在的不足和今后的研究方向。更多还原

【Abstract】 The flying capability of insects and birds is so excellent that we can benefit abundantly from their flying behavior. According to the principles of bionics, lots of new morphing aircrafts have been designed with the development of aerodynamic technology. As one follows the evolution of the aircraft, however, fixed geometry, high stiffness wings emerge as the dominant trait. As a result, air vehicles are optimized for specific flight conditions, such as the cruising condition. Flight dynamiscists have realized that changes in geometry of flight vehicles could provide significant improvement in flight efficiency. Therefore, researchers brought up the concept of wing shape control[1]. As an example, there comes the morphing aircraft with folding wings proposed by the Lockheed Martin Company. It is an unmanned combat air vehicle (UCAV), capable of long range cruising with unfolding wings, and fast diving with folded wings, and transition back for the long range cruising. The configuration has two foldable wing-sections that allow radical morphing of span and wetted area. The inner wing can fold approximately 130 degrees from the unfolded to the folded configuration, while the outer wing keeps the original horizontal status to achieve the 200% wing area changing. Comparing with conventional aircrafts, configuration morphing improves significantly the mission performance. The goal of this thesis is to simulate the unsteady flows and study the dynamic aerodynamic characteristics of the morphing aircraft during the movement of its wing’s folding/unfolding.The folding/unfolding movement of morphing aircraft is of strongly unsteady and nonlinear, so its computational grids have to be deformed with the wing morphing. Therefore, to simulate the unsteady flows over morphing aircraft, dynamic grid technique and corresponding efficient unsteady flow solver should be set up firstly. So this thesis is organized as follows:In the preface as chapter one of this thesis, the research background is discussed firstly in brief. Then the progress in hybrid mesh generation techniques, dynamic grid generation methods and the numerical methods for unsteady flows are reviewed. And the work of this paper is presented finally.In the second chapter, we introduce the static/dynamic hybrid mesh generation technique, including the fundamental strategy of dynamic hybrid mesh generation, static hybrid mesh generation, Delaunay graph generation and the coupling dynamic hybrid grid generation method of Delaunay graph mapping and local remeshing. At the end of this chapter, some examples of grid generation are shown, which are used in the following numerical simulations of this thesis. In the third chapter, an unsteady flow solver based on the hybrid dynamic grid is proposed, including the governing equations, spatial and time discretization scheme, geometric conservation law (GCL) for moving grid simulations, and boundary conditions. Some typical steady/unsteady test cases are simulated to validate the unsteady flow solver and the dynamic hybrid grid approach. The numerical results demonstrate the efficiency and accuracy of present method.In the fourth chapter, the unsteady flows over transonic morphing airfoils are simulated by adding some morphing models to the original airfoils (NACA0012 and RAE2822). From the idea of flow-roller effect in the boundary layer, we wish that these models could push backward the position of shock-wave on the leeward of the airfoils to increase the lift coefficient. Unfortunately, most of the results show that the morphing models pull the shock wave on the airfoil leeward forward, resulting in the decreasing of the lift coefficient. So these morphing models are not suitable for transonic airfoils with shock wave dominating the flow fields.In the fifth chapter, the morphing models are adopted on a typical subsonic three-element airfoil (30P30N) to find the helpful effects on the airfoil aerodynamic characteristics. By comparing the numerical results of left-travel wave model, right-travel wave model, left-travel compound wave model, right-travel compound wave model and local oscillation model, we find that the lift coefficients of 30P30N airfoil after stall can increase more or less.In the sixth chapter, numerical simulations over a morphing aircraft with foldable wings are carried out, and the dynamic aerodynamic characteristics are analyzed. Firstly, we design a simplified model of morphing aircraft according to the references, and then dynamic unstructured grids are generated by the dynamic hybrid grid generation technique presented in chapter two. After that, numerical simulations are undertaken with the unsteady flow solver, here the inviscid cases are considered only. The computational results demonstrate that the aerodynamic characteristics of the morphing aircraft change rapidly with the shock wave on the leeward of the wing moving forward during the wing folding/unfolding.In the last chapter, some concluding remarks are given, and the future work is discussed.更多还原