基于非均匀梁模型的二维柔性机翼固有振动分析

变体飞行器通过光滑连续的结构变形改变气动特性,从而提高飞行器的飞行性能,具有很大的应用前景.由于这类新概念飞行器主要通过改变自身结构形状以获得最佳工作性能的需求,因此具有变形大、质量轻等特点,较容易发生结构振动响应.本文研究了一种以柔性变后缘作为变体形式的二维柔性机翼等效建模方法,基于非均匀梁模型假设,建立了该柔性翼的动力学模型.通过利用Frobenius方法得到解析解及固有频率,并用有限元方法进行对比验证,发现前4阶固有频率的误差均在1%以内,每阶固有频率对应的振型一致.通过3D打印工程塑料ABS和硅胶蒙皮材料制备了柔性机翼结构件,并通过动态测量法和拉伸试验分别测定了打印材料和硅胶蒙皮材料的杨氏模量,搭建振动响应实验平台对制备的柔性机翼试验件进行振动试验.对比发现模型振动试验获得的基频与理论模型结果一致,并与有限元方法误差在3%以内.本文通过理论分析和实验验证,建立了二维柔性机翼等效建模方法,研究结果将为柔性变后缘结构动力学特性分析及其控制应用方面提供理论支持.     

低Re数下变弯度机翼的非定常气动特性实验研究

利用变弯度机翼模型及相关的风洞实验平台,开展了以弯度变化速率影响为重点的机翼非定常特性研究。实验结果显示,在低Re数(~105)下,机翼弯度非定常变化得到的升阻力系数曲线与准定常条件下的结果存在显著差异。具体表现为:准定常状态下,曲线表现出明显的可逆性;而弯度非定常变化时,曲线在弯度递增区和递减区之间存在明显的迟滞效应,而且随着变形速率的增加,这种迟滞也越明显。流场显示结果表明,这种小St数下出现的流动迟滞是由于弯度变形导致的流动分离的分离点相对机翼运动迟滞所造成的。这说明弯度变化时,分离流场结构的响应时间尺度与弯度变化周期相当,也揭示了该条件下机翼弯度变化对流动的抑制作用主要是通过改变分离区的大小来实现的。     

基于可变形蜂窝的柔性蒙皮力学性能分析与结构设计

变体飞机可以在飞行中充分改变外形获得最佳气动效率以适应变化的任务环境.覆盖在结构表面的蒙皮不仅要具有良好的面内方向柔性,产生满足设计变形量的光滑连续变形,同时要提供足够的垂直平面方向刚度,维持气动构型,并将气动载荷传递到下层结构.论文提出一种在十字形可变形蜂窝表面覆盖硅胶表层的结构作为柔性蒙皮,理论分析了该柔性蒙皮在面内方向的变形机理以及十字形可变形蜂窝的形状参数对其力学性能的影响,并与仿真和试验结果进行了比较.根据后缘变弯度机翼的设计要求,给出了柔性蒙皮的设计参数范围.结果表明该柔性蒙皮具有足够的面内方向变形能力和垂直平面方向承载能力,满足变弯度机翼后缘设计要求.     

基于分段进化的遗传算法在机翼气动外形设计上的应用

与传统的优化方法相比,遗传算法以其极强的鲁棒性、随机搜索特性以及优化结果的全局性等特点而在工程优化中得到越来越广泛的应用.标准遗传算法中使用的二进制编码类似于生物染色体的组成,使算法易于用生物遗传学理论加以解释,同时也使交叉、变异等遗传操作易于实现.此外,使用二进制编码还有助于充分发挥算法隐含的并行性.本文对传统遗传算法加以改进,在二进制编码下引入分段进化的概念,再配以高效的交叉、变异算子,充分发挥二进制编码固有优势的同时在很大程度上提高了算法的优化效率,并与Euler方程数值解法相结合,对机翼外形进行了气动优化设计.优化后机翼的升阻比有了显著提高,表明建立的优化模型是合理有效的.     

基于Voronoi cells的二维不规则自适应网格的生成及其应用

基于Voronoi cells的数据结构和算法，给出了一种二维不规则自适应网格的生成方法，用VisualC＋＋语言在微机上开发了Windows环境下网格自动生成的可视化软件。既可以得到Voronoi cells网格，也可得到相应的Delaunay triangles网格，网格生成的实例表明，本文方法所得到的网格非常适合于多尺度系统的流动问题的计算，具有较好的应用前景。     

两种椭圆翼型高速气动特性实验研究

新概念旋转机翼飞机的主机翼既能高速旋转作为旋翼,又可锁定作为固定翼,所以只能使用特殊的前后对称翼型。针对主机翼翼型的这一特殊要求,对16％相对厚度,相对弯度分别为0％和3％的两种椭圆翼型的高速气动特性进行了风洞实验研究,试验分别在中国空气动力研究发展中心FL-21风洞和荷兰代尔夫特大学TST-27风洞进行,采用表面测压和尾排型阻测量技术。试验结果的对比分析表明,有弯度椭圆翼型的升力和力矩特性优于无弯度椭圆翼型,而阻力特性和最大升阻比劣于无弯度椭圆翼型。试验结果为旋转机翼飞机主机翼翼型的选取提供了参考。     

低雷诺数下柔性翼型气动性能分析

基于流固耦合方法对吸力面5% 至95% 弦长处为三段柔性结构的NACA0012 翼型绕流进行了数值模拟,研究了不同弹性模量下柔性翼型的气动性能和结构响应. 结果表明：在大攻角下,翼面变形影响着翼型表面的非定常流场,起到延缓失速和提高升力的作用;失速后柔性翼的升力系数下降得较为缓慢,且柔性越大,升力系数下降得越平缓;适当减小弹性模量能够提高翼型的气动性能,然而弹性模量过小反而不利于翼型气动性能的提升,并且翼面会产生大幅度的振动.     

飞机机翼损伤的气动模型及故障诊断研究

为了确保机翼损伤后飞机的飞行安全,提出了一种在线的故障诊断方法. 首先,根据输入输出特性,采用遗忘因子递推最小二乘法对飞机故障后的气动导数进行辨识,建立了机翼损伤故障的数学模型;然后,结合多模型方法和中心差分卡尔曼滤波器（central difference Kalman filter,CDKF）各自的优点,实现对机翼损伤的故障诊断,并采用强跟踪滤波器在线更新CDKF 的采样点,以增强CDKF 的自适应能力. 最后,通过仿真结果验证了本文所提方法的有效性.     

二维自适应非结构网格DSMC并行算法研究

研究了二维自适应非结构网格DSMC并行算法实现的过程.首先提出了一类非结构网格自适应策略,有效降低了网格尺度对计算结果的影响,提高了流场的分辨率;然后基于PC-CLUSTER群机并行体系结构与消息传递库MPI并行环境,利用分区并行思想,设计了非结构网格DSMC并行算法,节约了计算时间.利用For-tran90的动态分配内存技术编制了通用计算程序;最后对过渡流域高超声绕流进行了数值模拟,计算结果初步验证了算法的可行性与有效性.     

动网格模拟风振对超大瘦高型冷却塔风荷载的影响

利用Fluent软件对超大瘦高型冷却塔的风荷载进行了CFD数值模拟,获得冷却塔外表面的三维流场特性和风压系数分布曲线,并与规范数据进行比较,以验证数值模拟的准确性;利用CFD动网格研究风振条件下冷却塔内外壁的风压分布。结果表明:考虑风振特性后,冷却塔外壁风压呈现增大的趋势,最大负压位置即流动分离点在考虑风振时产生了滞后;对于本文研究的上下开口结构而言,在考虑风振作用后内部风压系数的绝对值整体偏大,且内部高压区的位置发生了变化;不考虑风振时内部风压高压区发生在接近塔底的区域,而考虑风振特性后,内部风压高压区发生在接近塔顶的区域。这说明风振在一定程度上改变了冷却塔内部风压的分布。     

Mathematical Modeling of Time-Dependent Aerodynamic Loads on an Airfoil with Dynamic Deflection of a Control on the Trailing Edge

The linear problem of the time-dependent inviscid flow past a thin symmetric airfoil with a control on its trailing edge deflected in accordance with an arbitrary law is considered. The aerodynamic loads on the airfoil are calculated. The intensity of the vortex wake shed from the airfoil is determined by numerically solving a Volterra integral equation of the first kind. Questions of the mathematical modeling of the time-dependent aerodynamic loads in a form convenient for the joint solution of the problems of aerodynamics and flight dynamics are also considered. The results of the modeling are compared with the numerical solutions obtained.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 157–169.Original Russian Text Copyright © 2005 by Khrabrov.     

Evaluation of the Spectral Element Dynamic Model for Large-Eddy Simulation on Unstructured,Deformed Meshes

In this paper, the Spectral-Element Dynamic Model (SEDM), suited for Large-Eddy Simulation (LES) using Discontinuous Finite Element Methods (DFEM), is assessed using unstructured meshes. Five test cases of increasing complexity are considered, namely, the Taylor-Green vortex at Re =?5000, the turbulent channel flow at Re_τ =?587, the circular cylinder in cross-flow at Re_D =?3900, the square cylinder in cross-flow at Re_D =?22400 and the channel with periodic constrictions at Re_h =?10595. Various discretization parameters such as the grid spacing, polynomial degree and numerical flux are assessed and very accurate results are reported in all cases. This consistency in the results demonstrates the versatility of the SEDM approach and its ability to gage the actual resolution and quality of the mesh and, accordingly, to introduce an amount of sub-grid dissipation which is adapted to the spatial discretization considered.     

扑翼飞行器带翼刀机翼气动特性实验研究

通过进行微型扑翼飞行器低速风洞试验,研究了带弯度机翼下翼面翼刀对扑翼飞行器升阻特性的影响。文中进行了带翼刀机翼和不带翼刀机翼在不同迎角下的风洞吹风试验。试验结果表明,带翼刀机翼升力系数大于不带翼刀机翼升力系数,从而证明了翼刀可以阻止机翼下表面气流展向流动,起到增加机翼升力的作用。当扑翼在小迎角飞行时,带翼刀机翼可以有效地提高扑翼的气动效率,改善扑翼的飞行性能。研究结果可为带翼刀机翼在扑翼飞行器上的应用提供技术支持。     

Supersonic Flow Past a Bent Delta Wing and Its Aerodynamic Characteristics

The supersonic flow past a bent delta wing and its aerodynamic characteristics, both local and integral, are studied using approximate analytic estimates and numerical calculations. The flow regimes with the shock attached to the leading edges are considered. It is established that at M = 4–6 and angles of attack as high as 6° the lift-drag ratio of the wing can be increased by 10% by deflecting the wing nose downwards. This is confirmed by the results obtained earlier in the hypersonic thin-shock-layer approximation. The effect is also obtained in calculations made within the framework of the Navier-Stokes equations.     

柔性扑翼的气动特性研究

以往扑翼的气动力计算研究都很少考虑扑翼的柔性,而在鸟的扑翼动作中,在外加气动力和鸟自身的扑动力作用下,扑翼的柔性变形相当大。本文在原有匀速刚性模型的基础上,提出考虑了扑翼扑动速率变化和形状变化的扑翼分析模型,使之更接近鸟翼柔性扑动真实情况。通过计算分析气动特性发现,控制适当的话,柔性变形能大大改善扑翼的气动性能。本文通过模拟鸟扑翼的柔性运动,计算了时柔性扑翼气动力以及平均升力系数和平均推力系数随着扑动角、倾斜角等参数变化的情况,从而从气动的角度解释了为什么鸟在不同的飞行阶段扑翼规律各不相同,并为柔性扑翼飞行器的设计提供了理论依据。     

Aerodynamic Performance of a Gliding Swallowtail Butterfly Wing Model

In the present study, we perform a wind-tunnel experiment to investigate the aerodynamic performance of a gliding swallowtail-butterfly wing model having a low aspect ratio. The drag, lift and pitching moment are directly measured using a 6-axis force/torque sensor. The lift coefficient increases rapidly at attack angles less than 10° and then slowly at larger attack angles. The lift coefficient does not fall off rapidly even at quite high angles of attack, showing the characteristics of low-aspect-ratio wings. On the other hand, the drag coefficient increases more rapidly at higher angles of attack due to the increase in the effective area responsible for the drag. The maximum lift-to-drag ratio of the present modeled swallowtail butterfly wing is larger than those of wings of fruitfly and bumblebee, and even comparable to those of wings of birds such as the petrel and starling. From the measurement of pitching moment, we show that the modeled swallowtail butterfly wing has a longitudinal static stability. Flow visualization shows that the flow separated from the leading edge reattaches on the wing surface at α < 15°, forming a small separation bubble, and full separation occurs at α ≥ 15°. On the other hand, strong wing-tip vortices are observed in the wake at α ≥ 5° and they are an important source of the lift as well as the main reason for broad stall. Finally, in the absence of long hind-wing tails, the lift and longitudinal static stability are reduced, indicating that the hind-wing tails play an important role in enhancing the aerodynamic performance.     

飞机机翼气动外形优化设计研究

本文首先对某飞机原机翼外形进行了详尽的气动分析计算,然后确定了设计思路和方案,探讨了后掠角变化对机翼气动性能的影响,研究选定了减小外翼后掠角的机翼新平面形状,采用先进的CFD软件优化机翼的气动设计,根据不同设计思想进行了多个机翼的外形优化,包括新的翼剖面和弯扭配置,最后将优化设计结果与原机翼进行了对比,对比结果表明,以Q5-M2T和Q5-N2T为代表的优化结果取得了十分理想的改进效果,优化机翼提高了气动性能,机翼升阻比提高了20%-30%,满足了飞机载弹量增大后性能仍可以全面提高的设计要求。     

Direct Numerical Simulation of Turbulent Flow over a Rectangular Trailing Edge

This paper describes a direct numerical simulation (DNS) study of turbulent flow over a rectangular trailing edge at a Reynolds number of 1000, based on the freestream quantities and the trailing edge thickness h; the incoming boundary layer displacement thickness δ^* is approximately equal to h. The time-dependent inflow boundary condition is provided by a separate turbulent boundary layer simulation which is in good agreement with existing computational and experimental data. The turbulent trailing edge flow simulation is carried out using a parallel multi-block code based on finite difference methods and using a multi-grid Poisson solver. The turbulent flow in the near-wake region of the trailing edge has been studied first for the effects of domain size and grid resolution. Then two simulations with a total of 256 × 512 × 64 (∼ 8.4×10⁶) and 512 × 1024 × 128 (∼ 6.7×10⁷) grid points in the computational domain are carried out to investigate the key flow features. Visualization of the instantaneous flow field is used to investigate the complex fluid dynamics taking place in the near-wake region; of particular importance is the interaction between the large-scale spanwise, or Kármán, vortices and the small-scale quasi-streamwise vortices contained within the inflow boundary layer. Comparisons of turbulence statistics including the mean flow quantities are presented, as well as the pressure distributions over the trailing edge. A spectral analysis applied to the force coefficient in the wall normal direction shows that the main shedding frequency is characterized by a Strouhal number based on h of approximately 0.118. Finally, the turbulence kinetic energy budget is analysed. Received 4 March 1999 and accepted 27 October 2000