通过自适应变体实现飞行器气动特性的提升一直以来是国内外先进飞行器研究的热点，其中最受关注且可实现的两种变体方式是变后掠和外翼的折叠。目前，国内外关于折叠翼的研究主要集中在关于洛克希德·马丁公司所提出的Z型折叠翼无人机模型的模态分析及其颤振特性的分析。早期的折叠翼颤振分析通常利用Nastran的气动弹性计算序列开展基于面元法的颤振特性计算，该计算方法为频域方法，即假设结构做简谐运动，使用线化的频域气动力模型开展颤振特性分析。传统的液压驱动的Z型折叠翼所搭载的沉重的铰链驱动系统，对舰载飞行器的正常运行造成了极大的负担，对飞行员的操控能力以及飞行器的综合性能的要求特别之高，存在诸多弊端。近期，NASA发展了形状自适应的L型折叠机翼，并顺利开展了折叠翼样机的飞行试验，由于相关技术和试验数据并未公开，本文借用L型折叠翼的概念，采用准定常假设，利用苏-33舰载机的翼板几何轮廓及适用于跨声速的NACA64008A翼型，建立各折叠角对应的几何模型，并相应地生成气动网格和结构有限元模型，完成L型折叠翼的颤振计算的前期准备工作。

在L型折叠翼的气动计算章节中，所采用的气动力求解方法并不是一般Z型折叠翼颤振研究中的面元法。由于折叠翼的外翼需要相对内翼发生运动，折叠后的外翼表面的流场与0°折叠角时的相比更为复杂，需要考虑内外翼之间的流动相互干扰。即使采用准定常假设，也仍然会出现复杂的流动特性和气动弹性特性，而非线性的流动问题难以用线化模型进行求解，因此，本文围绕折叠翼颤振这一问题，开展基于CFD/CSD耦合方法的折叠翼颤振计算工作，厘清折叠翼气动特性以及气动弹性特性受折叠角、攻角等参数影响下的变化规律。

围绕L型折叠机翼开展亚声速气动特性研究，探究攻角、折叠角对低亚声速飞行状态下的折叠翼的气动特性的影响规律，并比较高亚声速域飞行时，不同折叠角形态的折叠翼的流场特性(如机翼周围流线及翼面压力分布)。通过比较发现，尽管随着折叠角增大，折叠翼获得的升力会有大幅度的减少，由于阻力系数同样大幅下降，当内外翼折叠成一个较大的锐角时，机翼的升阻比反而维持在一个较高的水平。此外，随着折叠角增大，机翼在达到失速迎角时获得的升力也越小，且失速迎角也有轻微的降低的趋势。当L型变体翼的折叠角继续增大,至内外翼比较接近的位置时，其发生失速的风险也越大。

利用有限元软件Patran/Nastran生成不同折叠角形态的折叠翼有限元模型，分别计算取值大小不同的弹性模量下，各折叠角形态机翼的前四阶模态频率，对比发现弹性模量的取值仅影响频率大小，但不改变前四阶模态频率随折叠角变化的规律。当折叠角为120°时，一阶与二阶模态频率几乎相同。当折叠成120°的L型机翼在气动力作用下发生随时间变化的振动时，其二阶振型的运动或变形会对一阶振型的运动或变形产生直接的影响。

最后，为了解跨声速飞行状态下，考虑结构弹性变形的L型折叠翼气动弹性特性，开展CFD/CSD紧耦合的气动弹性计算工作。将结构模态所对应位移视作广义结构动力学方程的待求解变量，在每一个物理时间步内进行该方程的求解。同时采用二阶时间离散格式求解N-S方程，使得双向流固耦合的整体时间精度达到二阶。在马赫数0.96的来流条件下，通过对比不同折叠角的颤振临界速度，可以找出折叠翼气动弹性特性关于折叠角等参数的变化规律，为将来自适应变体的L型折叠翼研究提供有益的参考。

The improvement of aerodynamic characteristics of aircraft through adaptive morphing approaches has always been a hot topic in the research of advanced aircrafts in China and abroad. Among them, the two most concerned and achievable approaches to changing the structure of wing are variable-sweeping backward and folding upwards or downwards the outer wing. At present, the research on folding wing mainly focuses on the modal analysis and flutter characteristics of the Z-shaped folding wing UAV model proposed by Lockheed Martin Corporation. The early flutter analysis of the folding wing usually carried out the flutter characteristics calculation based on the panel method through the aerodynamic calculation sequence of Nastran. The calculating method is called the frequency domain method, that is, assuming that the structure does harmonic motion, the linear frequency domain aerodynamic model is used to carry out the flutter characteristics analysis. The traditional flexible hinged Z-shaped folding wing is loaded with a heavy hydraulic drive system., which causes a great burden on the normal operation of shipborne aircraft. The requirements for the control ability of pilots and the comprehensive performance of aircraft are particularly high, and there are many drawbacks. Recently, NASA has developed the shape-adaptive L-shaped folding wing, and successfully carried out the flight test of the prototype. Since the relevant technologies and test data are not disclosed, the related work in this paper uses the concept of adaptive L-shaped folding wing, adopts the quasi-steady assumption while the wing plate uses the geometry of Su33 carrier-based aircraft and the NACA64008A airfoil suitable for transonic flight to establish the geometric model corresponding to each folding angle. And then, it would be easy to generate the aerodynamic grid and structural finite element model accordingly, so as to complete the preliminary preparation for the flutter calculation of L-shaped folding wing.

In the aerodynamic calculation section of L-shaped folding wing, the aerodynamic force solution method used is not the panel method in the flutter research of Z-shaped folding wing. Since the outboard wing needs to move relative to the inner wing, the flow field on the surface of the folding wing is more complex than that completely unfolded. Besides, the flow interference between the inner and outer wings should be considered. Even if the quasi-steady assumption is adopted, there will still be complex flow characteristics and aeroelastic characteristics, and the nonlinear flow problem is difficult to solve by linear model. Therefore, this paper focuses on the flutter of folding wings, and carries out the flutter calculation of folding wings based on CFD/CSD coupling method to clarify the aerodynamic characteristics and aeroelastic characteristics of folding wings under the influence of folding angle and attack angle.

The subsonic aerodynamic characteristics of L-shaped folding wing has been studied to explore the influence of attack angle and folding angle on the aerodynamic characteristics of folding wing during low subsonic region and to compare the flow field characteristics (such as the streamlines around the wings and the pressure distribution on the wing surface) of the wing with different folding angles in high subsonic region. Through comparing those different cases, it is found that although the lift force obtained by the folding wing decreases greatly with the increase of the folding angle, the lift to drag ratio of the wing remains at a high level when the inner and outer wing are folded into a large acute angle, because the drag coefficient also decreases greatly. Additionally, with the increase of the folding angle, the lift force of the wing becomes smaller when it reaches the stall angle of attack, and the stalling angle of attack also has a slight tendency to decrease. When the folding angle of the L-shaped morphing wing continues to increase and the inner and outer wings get close to each other, the risk of stall of the folding wing will also increase.

Through the finite element software Patran/Nastran, the finite element models of wings with different folding angles are generated, and the first four order modal frequencies of wings with different folding angles are calculated under different elastic modulus. It is found that the value of touch only affects the frequency, but does not change the law of the first four order modal frequencies with the folding angle. When the folding angle is 120°, the first-order and second-order modal frequencies are almost the same. When the L-shaped wing folded into 120° vibrates with time under aerodynamic force, the motion or deformation of the second-order mode will have a direct impact on the motion or deformation of the first-order mode

Finally, in order to work out the aeroelastic characteristics of L-shaped folding wing considering structural elastic deformation in transonic flight, the CFD / CSD tight coupling aeroelastic calculation is carried out. The structural modal displacement is regarded as a variable in generalized structural dynamic equation, and the equation will be solved during one physic time step. At the same time, the second-order time discretization scheme is used to solve the N-S equation, so that the overall time accuracy of fluid-solid two-way coupling reaches second order. By comparing the flutter critical speeds of different folding angles under the inflow condition of Mach number 0.96, the variation law of the aeroelastic characteristics of folding wing with parameters such as folding angle might be found. And the law provides useful experience for the adaptive L-shaped folding wing in the future.