Experimental investigation of influence of strake wings on self-induced roll motion at high angles of attack

The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.     

典型结构的高频响应研究

利用ＮＡＳＴＲＡＮ软件得到一简支梁从低频到高频的频响特性，研究了不同有限元网格划分对结构高频特性的影响，并通过ＳＥＡ法、有法元法以及解析解的对比揭示了ＳＥＡ法在高频响应预示中的有效性。然后以耦合梁为例，通过有限元法得到两个梁之间的能量传递，并进而得到ＳＥＡ所需的耦合损耗因子；将有限元计算结果和ＳＥＡ结果对比验证了该方法的有效性，以其建立一种用有限元法获得ＳＥＡ参数的新途径。此外，研究了集中质量和不     

Fuzzy压缩映象不动点定理

本文将Fuuzy压缩原理进行了推广，首次通过引入一个Fuzzy ε上半连续函数和Fuzzy链空间成功的证明了Fuzzy数值函数的不动点定理。     

High-order implicit discontinuous Galerkin schemes for unsteady compressible Navier–Stokes equations

Efficient solution techniques for high-order temporal and spatial discontinuous Galerkin(DG) discretizations of the unsteady Navier–Stokes equations are developed. A fourth-order implicit Runge–Kutta(IRK) scheme is applied for the time integration and a multigrid preconditioned GMRES solver is extended to solve the nonlinear system arising from each IRK stage. Several modifications to the implicit solver have been considered to achieve the efficiency enhancement and meantime to reduce the memory requirement. A variety of time-accurate viscous flow simulations are performed to assess the resulting high-order implicit DG methods. The designed order of accuracy for temporal discretization scheme is validate and the present implicit solver shows the superior performance by allowing quite large time step to be used in solving time-implicit systems. Numerical results are in good agreement with the published data and demonstrate the potential advantages of the high-order scheme in gaining both the high accuracy and the high efficiency.     

扑翼非定常气动特性的实验研究

扑翼的动态特性使其具有与固定翼完全不同的飞行模式,为了研究扑翼在扑动周期内的非定常气动特性,建立基于虚拟仪器的扑翼风洞实验测控系统,能够实现对气动力、扑动角度、功率等物理量的实时测量;以斯特劳哈尔数作为扑翼非定常程度的度量标准,并根据斯特劳哈尔数的定义完成扑翼在不同扑动幅度、扑动频率和来流速度条件下的风洞实验;分析扑翼在不同条件下的升力、推力及推进效率,进而得出斯特劳哈尔数对扑翼气动特性的影响规律。结果表明:扑翼的气动力随斯特劳哈尔数的增大而显著增大;当斯特劳哈尔数处于特定范围内时,扑翼具有较高的推进效率。     

大型飞机铰链下垂前缘多段翼型气动优化设计与研究

随着增升装置的发展,新型商用飞机机翼内侧采用了结构简单的铰链下垂前缘,与使用最多的前缘缝翼相比,它具有减阻降噪,提高升阻比等优点。针对大型飞机铰链下垂前缘翼型进行了气动优化设计及数值研究。首先设计出铰链下垂前缘的二维翼型,然后通过iSIGHT平台对翼型进行气动优化,分析铰链下垂前缘翼型的低速气动特性,并且得出最佳翼型,最后与前缘缝翼翼型的气动性能进行对比,说明使用铰链下垂前缘的可行性。     

长时间小过载条件下发动机流场特征及绝热层烧蚀分析

以揭示固体火箭发动机在飞行条件下绝热层的异常烧蚀特性为目的,针对小过载、长作用时间条件下大长径比流道的发动机开展了三维两相流场的数值模拟研究,详细分析了发动机内流道内不同区域的颗粒聚集特征,并结合发动机失效部位处绝热层的烧蚀形貌进行了失效模式分析,针对性地提出了改进措施.研究结果表明:(1)不同过载条件下发动机内颗粒聚集和分布状态受过载大小和发动机流道结构共同作用且影响规律复杂,所引起的绝热层异常烧蚀模式和机理不同,特别是小过载长作用时间条件下的异常烧蚀需要引起设计者重视.(2)颗粒聚集在绝热层表面的换热或冲蚀都将引起绝热层局部烧蚀加剧,形成的“凹坑或凹槽”烧蚀形貌会造成颗粒的二次聚集效应,进而加剧烧蚀过程.(3)通过增加发动机旋转动作和局部绝热层加厚,可以提高发动机的飞行安全性.     

Subsonic impulsively starting flow at a high angle of attack with shock wave and vortex interaction

Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently, a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.     

Hydraulic piston pump in civil aircraft: Current status,future directions and critical technologies

The piston pump is the key power component in the civil aircraft hydraulic system, and the most common pump used in the aviation field is the pressure compensated variable displacement type. In this review paper, a basic introduction to the civil aircraft piston pump is presented, including the classification, structure, working principle, design features, and achievements by some research groups. Then, the future directions of the aircraft pump are reported from various perspectives. Further, the critical technologies are analyzed and summarized in detail from six thrust areas: friction couples, noise reduction, inlet boost, thermal management, fault diagnosis and health management, and mechanical seal. Finally, the challenges and limitations of the research on the aircraft pump are discussed to provide valuable insight for future scholars.     

Study on effects of thickness on airfoil-stall at low Reynolds numbers by cusp-catastrophic model based on GA(W)-1 airfoil

The phenomena of an airfoil stall present the behaviors of catastrophe and hysteresis at low Reynolds numbers. Numerical simulation results of two-dimensional airfoil GA(W)-1 show that the width of the hysteresis loop of airfoil stall will gradually decrease and even disappear with the decrease of thickness ratio. These nonlinear characteristics are in accordance with the topological features of the cusp catastrophic model. According to the topological invariant principle, a novel topological mapping method is developed to establish the mapping relationship between cusp catastrophic model and stall characteristics of the airfoil, then the effect of thickness ratio on airfoil stall is successfully described quantitatively by cusp catastrophic model. Further, based on the established topological mapping relationship, combined with the mean flow field of the airfoil stall, potential function approach of cusp catastrophic model is first introduced to interpret the catastrophe and hysteresis of the airfoil stall, and it is found that as the thickness ratio decreases, the system's maximal potential energy gradually disappears, and the short separation bubble at the leading edge of the airfoil changes to long separation bubble, so the airfoil stall changes from a bistable system to a monostable system.