An experimental study of elastic properties of dragonfly-like flapping wings for use in biomimetic micro air vehicles (BMAVs)

This article studies the elastic properties of several biomimetic micro air vehicle (BMAV) wings that are based on a dragonfly wing. BMAVs are a new class of unmanned micro-sized air vehicles that mimic the flapping wing motion of flying biological organisms (e.g., insects, birds, and bats). Three structurally identical wings were fabricated using different materials: acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and acrylic. Simplified wing frame structures were fabricated from these materials and then a nanocomposite film was adhered to them which mimics the membrane of an actual dragonfly. These wings were then attached to an electromagnetic actu-ator and passively flapped at frequencies of 10–250 Hz. A three-dimensional high frame rate imag-ing system was used to capture the flapping motions of these wings at a resolution of 320 pixels × 240 pixels and 35000 frames per second. The maximum bending angle, maximum wing tip deflection, maximum wing tip twist angle, and wing tip twist speed of each wing were measured and compared to each other and the actual dragonfly wing. The results show that the ABS wing has considerable flexibility in the chordwise direction, whereas the PLA and acrylic wings show better conformity to an actual dragonfly wing in the spanwise direction. Past studies have shown that the aerodynamic performance of a BMAV flapping wing is enhanced if its chordwise flexibility is increased and its spanwise flexibility is reduced. Therefore, the ABS wing (fabricated using a 3D printer) shows the most promising results for future applications.     

Morphing wing flaps for large civil aircraft: Evolution of a smart technology across the Clean Sky program

Morphing wing structures are widely considered among the most promising technologies for the improvement of aerodynamic performances in large civil aircraft. The controlled adaptation of the wing shape to external operative conditions naturally enables the maximization of aircraft aerodynamic efficiency, with positive fallouts on the amount of fuel burned and pollutant emissions. The benefits brought by morphing wings at aircraft level are accompanied by the criticalities of the enabling technologies, mainly involving weight penalties, overconsumption of electrical power, and safety issues. The attempt to solve such criticalities passes through the development of novel design approaches, ensuring the consolidation of reliable structural solutions that are adequately mature for certification and in-flight operations. In this work, the development phases of a multimodal camber morphing wing flap, tailored for large civil aircraft applications, are outlined with specific reference to the activities addressed by the author in the framework of the Clean Sky program.The flap is morphed according to target shapes depending on aircraft flight conditions and defined to enhance high-lift performances during takeoff and landing, as well as wing aerodynamic efficiency during cruise. An innovative system based on finger-like robotic ribs driven by electromechanical actuators is proposed as morphing-enabling technology; the maturation process of the device is then traced from the proof of concept to the consolidation of a true-scale demonstrator for pre-flight ground validation tests. A step-by-step approach involving the design and testing of intermediate demonstrators is then carried out to show the compliance of the adaptive system with industrial standards and safety requirements. The technical issues encountered during the development of each intermediate demonstrator are critically analyzed, and justifications are provided for all the adopted engineering solutions. Finally, the layout of the true-scale demonstrator is presented, with emphasis on the architectural strengths, enabling the forthcoming validation in real operative conditions.     

大型民机翼型变弯度气动特性分析与优化设计

为了提高飞机巡航过程中升力系数、马赫数变化后的气动效率,大型民用运输机开始采用机翼变弯度技术。以典型远程宽体客机翼型为例,研究了翼型后缘变弯度对气动性能与压力分布的影响。利用代理模型建立了不同巡航设计工况下,翼型后缘弯度与气动性能的关系。以此为基础,提出了基于代理模型的大型民机翼型变弯度设计优化方法。算例研究表明,在给定巡航升力系数与马赫数下,该方法可以预测出翼型的最佳弯度,从而改善非设计点气动性能。该方法对大型民机机翼变弯度构型设计工作有一定的工程意义。     

A compliant polymorphing wing for small UAVs

This paper presents the development of a novel compliant polymorphing wing capable of chord and camber morphing for small UAVs. The morphing wing can achieve up to 10% chord extension and ±20° camber changes. The design, modeling, sizing, manufacturing and mechanical testing of the wing are detailed. The polymorphing wing consists of one continuous front spar fixed to the fuselage and a rear spar on each side of the wing. Each rear spar can translate in the chordwise direction (chord morphing) and rotate around itself (camber morphing). A flexible elastomeric latex sheet is used as the skin to cover the wing and maintain its aerodynamic shape whilst allowing morphing. The loads from the skin are transferred to the spars using the compliant cellular ribs that support the flexible skin and facilitate morphing. Pre-tensioning is applied to the skin to minimize wrinkling when subject to aerodynamic and actuation loads. A rack and pinion actuation system, powered by stepper motors, is used for morphing. Aero-structural design, analysis and sizing are conducted. Performance comparison between the polymorphing wing and the baseline wing (non-morphing) shows that chord morphing improves aerodynamic efficiency at low angles of attack while camber morphing improves efficiency at high angles of attack.     

民用客机可变弯度机翼优化设计研究

远程宽体客机在实际飞行状态下,机翼变弯度有效减阻能够提升客机性能和飞行品质。以全机配平构型为研究对象,基于襟翼、扰流板偏转建立变弯度模型;采用 RANS 方程实现阻力的精确求解并建立响应面模型,对不同升力系数、马赫数的多个飞行状态进行变弯度减阻优化;在此基础上,对实际飞行过程中变弯度操作需求及综合减阻性能进行分析,并采...     

新型无尾联接翼布局气动特性研究

提出一种上下错开的无尾联接翼,即前翼或者后翼上反一定角度,使得前后翼垂直方向的相对距离从翼根处开始到翼梢处逐渐增大,以达到减小前后翼气动干扰的目的,搭接的小翼具有翼梢小翼作用,可有效减小诱导阻力。采用基于RANS方程的数值方法,研究了前后翼分别上反10°,20°和30°时对总体气动特性的影响,结果表明,当前翼上反且上反角为30°时其联接翼系统气动性能最佳。对该联接翼布局在Ma=0.85,0.95和1.20下进行了数值分析,结果表明,其升力系数变化较小,阻力系数在Ma0.85后才急剧增大,有应用于未来跨声速/超声速客机布局的潜力。     

倾转旋翼机前飞动力学稳定性分析

倾转旋翼机的机翼端部装有一个可倾转的旋翼.所建立的倾转旋翼机前飞动力学稳定性分析简化模型由一个机翼和一个螺旋桨旋翼组成.机翼承受垂向弯曲、弦向弯曲和扭转变形,螺旋桨旋翼的桨叶认为是刚性的并承受一阶挥舞和摆振.机翼和螺旋桨旋翼的空气动力学载荷由准定常片条理论得到.利用此模型在高入流状态下建立运动微分方程,对倾转旋翼机在前飞状态下的动力学稳定性进行计算,计算结果与Bell公司试验结果基本一致,表明该模型可用于倾转旋翼机的前飞动力学稳定性分析.      

超临界机翼多目标气动优化设计的策略与方法

超临界机翼的气动设计十分复杂,往往需要借助于有效的优化手段。然而,优化方法本身往往无法直接表达真实完整的设计意图,因此需要将工程需求和约束转换为优化方法所能处理的数学形式。本文首先探讨了梯度优化方法和进化类优化方法在气动优化中的表现。之后简要总结了前人在飞机气动设计中提出的准则和要求,并基于压力分布形态定义了超临界机翼气动设计的关键特征及定量要求,探究其在超临界机翼气动优化设计中的应用效果。研究结果表明,在多目标优化中引入面向压力分布形态特征的目标和约束,能有效引导优化体现工程设计思想,进而提高优化效率。     

排式充气机翼的高效气动布局研究

为了提高充气机翼的刚度特性,需要采用较大厚度的翼型,但厚翼型气动效率整体上又不太高。探讨一种适用于低速充气类飞行器的排式双翼布局方案,并尝试给予后翼一定的初始安装偏转角,同时还研究了双翼相对位置以及翼型特性对该排式双翼布局方案的影响。数值模拟结果表明,后翼前缘驻点附近的高压区增大了前翼下表面的压力,使此种布局较普通单翼布局在中小迎角范围内可以明显提高飞行器的升力和升阻比,其中迎角4°时可将升阻比提高62.8%,而给后翼2°的偏转角可使将升阻比提高幅度达到70.5%。同时,双翼相对位置对飞行器气动性能的影响较为敏感。此外,翼型厚度越大,弯度越小,所提出的排式双翼布局方案提高升阻比的效果越明显。综合效果来看,文中探讨的布局可为充气飞机的设计提供一个新思路。     

Effect of an end plate on surface pressure distributions of two swept wings

A series of wind tunnel tests was conducted to examine how an end plate affects the pressure distributions of two wings with leading edge(LE) sweep angles of 23° and 40°. All the experiments were carried out at a midchord Reynolds number of 8×10~5, covering an angle of attack(AOA) range from -2° to 14°. Static pressure distribution measurements were acquired over the upper surfaces of the wings along three chordwise rows and one spanwise direction at the wing quarter-chord line. The results of the tests confirm that at a particular AOA, increasing the sweep angle causes a noticeable decrease in the upper-surface suction pressure. Furthermore, as the sweep angle increases, the development of a laminar separation bubble near the LEs of the wings takes place at higher AOAs. On the other hand, spanwise pressure measurements show that increasing the wing sweep angle results in forming a stronger vortex on the quarter-chord line which has lower sensitivity to AOA variation and remains substantially attached to the wing surface for higher AOAs than that can be achieved in the case of a lower sweep angle. In addition, data obtained indicate that installing an end plate further reinforces the spanwise flow over the wing surface, thus affecting the pressure distribution.     

一个计算喷气翼的考虑非线性效应的涡格法

 本文发展了确定喷气翼气动性能的三维非线性方法。用附着涡和自由涡系统代表翼面、喷流、尾流和翼尖涡,解出弦向和展向载荷分布;同时解出喷流、尾流和翼尖涡的形状。所得结果在大展弦比条件下与实验及其他理论结果相符。本法可应用于各种展弦比、喷流角以及部分喷气情况下。     

Aerodynamic benefits of adaptive wing technology

Especially in the case of large transonic transport aircraft, flight conditions change considerably during a typical mission. This is accounted for by multiple but fixed design points which compromise aircraft performance. Employing adaptive wing technology where the wing geometry, or other means of flow control, adjusts the flow development to the changing freestream and load conditions allows us to explore fully the flow potential at each point of the flight envelope. Various means of flow control by geometric adaptation and by direct boundary layer control have been investigated within the German national program ADIF and the EU-project EUROSHOCK II and their potential explored. Here, corresponding results are presented and discussed, indicating the applicability and benefits of the adaptive control methods considered. It is also demonstrated that, generally, flow control must be adaptive to work in real aeronautical conditions since these conditions change within the mission flight envelope.     

Recent progress in flapping wing aerodynamics and aeroelasticity

Micro air vehicles (MAVs) have the potential to revolutionize our sensing and information gathering capabilities in areas such as environmental monitoring and homeland security. Flapping wings with suitable wing kinematics, wing shapes, and flexible structures can enhance lift as well as thrust by exploiting large-scale vortical flow structures under various conditions. However, the scaling invariance of both fluid dynamics and structural dynamics as the size changes is fundamentally difficult. The focus of this review is to assess the recent progress in flapping wing aerodynamics and aeroelasticity. It is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation. While in classical stationary wing theory, the tip vortices (TiVs) are seen as wasted energy, in flapping flight, they can interact with the LEV to enhance lift without increasing the power requirements. Surrogate modeling techniques can assess the aerodynamic outcomes between two- and three-dimensional wing. The combined effect of the TiVs, the LEV, and jet can improve the aerodynamics of a flapping wing. Regarding aeroelasticity, chordwise flexibility in the forward flight can substantially adjust the projected area normal to the flight trajectory via shape deformation, hence redistributing thrust and lift. Spanwise flexibility in the forward flight creates shape deformation from the wing root to the wing tip resulting in varied phase shift and effective angle of attack distribution along the wing span. Numerous open issues in flapping wing aerodynamics are highlighted.     

民用飞机增升装置载荷设计技术研究

增升装置是机翼上用来改善气流状态和增加升力的一套活动面板,可在飞机起飞、着陆和低速机动飞行时增加机翼剖面弯曲度和有效迎角,因此对提升大型民用飞机的起飞和降落等低速性能,包括进场姿态有着决定性的影响。飞机在起降中一般要求尽量减小飞行速度和缩短滑行距离,同时要达到比较大的升力系数,这就意味着增升装置此时也具有较大的偏度,作用在上面的载荷也会比较大。因此,大型民用飞机增升装置的载荷计算是其设计工作中的重中之重,在民用飞机载荷设计过程中有非常重要的意义。主要介绍了民用飞机增升装置载荷的计算原理及设计方法,给出了一套襟缝翼气动和惯性载荷的工程算法。     

伸缩弹翼巡航导弹气动外形优化研究

基于一种伸缩弹翼改变巡航导弹外形的概念,提出超声速巡航与亚声速盘旋相结合的飞行任务,使用Missile Datcom作为气动计算的工具,分别对固定翼、两级伸缩翼和三级伸缩翼的外形参数进行了优化,使三种不同弹翼导弹完成相同飞行任务的燃料消耗分别最小,优化方法选取遗传算法与模式搜索法相结合的混合优化策略.优化结果显示,两级、三级伸缩翼巡航导弹相对固定翼巡航导弹燃料消耗量分别减少7.8%和12%,表明伸缩弹翼有效提高了巡航导弹在整个飞行任务中的气动性能.     

基于非定常面元/黏性涡粒子法的低雷诺数滑流气动干扰

针对太阳能无人机螺旋桨滑流与机翼的气动干扰,考虑了低雷诺数流动下气体黏性和压缩性影响,并根据黎曼边界条件和涡量等效原则建立了能够快速计算分析螺旋桨-机翼气动干扰的非定常面元/黏性涡粒子的混合方法。首先使用有试验数据的风洞模型以及数值模拟技术对混合方法进行验证,在此基础上研究了不同安装位置与工况下螺旋桨与机翼的气动干扰。结果表明:螺旋桨对轴向气流的加速以及滑流诱导的上洗和下洗效应使机翼气动力呈现出增升增阻的现象,机翼升阻比有所下降。较大的弦向间距以及较高的垂直安装位置在减缓机翼升阻比下降的同时也使得螺旋桨拉力有所减小。对于多个螺旋桨的气动干扰,不同的桨叶旋转方向导致机翼气动力不同的变化规律,当旋转方向与机翼翼尖涡反向时,螺旋桨滑流能够抑制翼尖涡的强度,提高机翼气动效率。     

前翼对飞机纵向气动特性和机翼载荷影响研究

利用ARGON和MGAERO计算了三翼面布局飞机气动特性和机翼载荷,给出了有前翼、无前翼布局全机气动特性和机翼环量分布。研究分析了前翼对全机气动特性、机翼分布载荷的影响规律,得到了一些重要的结论,可用于飞机型号设计。     

串列翼飞行器机翼耦合特性研究

串列翼飞行器由于其前后翼以及机身之间的相互干扰,气动特性复杂且难以预测。针对一款串列翼飞行器,以前后翼之间的垂直距离为变量,设计了五种气动布局,并使用CFD方法进行了数值模拟计算。通过对五种布局升阻特性与俯仰特性的比较及分析,发现前后翼垂直方向距离会显著影响整机升阻比、俯仰稳定性、气动中心位置以及压力中心位置。两翼间垂直方向上的距离越大,飞行器升阻比越高,且气动中心更加靠后。而在两翼间距离相同的情况下,前翼在下的布局拥有更高的升阻比,而前翼在上的布局拥有更好的俯仰静稳定性。     

气动载荷压心外移对机翼结构重量的影响

以某型飞机机翼气动分布载荷和结构重量为基础,研究气动载荷压心外移对机翼结构重量的影响,得到了气动压心外移量与机翼结构增重之间的函数关系。这个结论可以为其他型号的民机机翼设计提供参考依据。     

微型飞行器小展弦比机翼的低雷诺数气动力特性分析

以固定机翼式微型飞行器的气动设计为研究背景,对小展弦比薄机翼的低雷诺数气动力特性进行了数值分析.不可压粘性绕流的求解采用了人工压缩性方法,其中对流项的离散应用了三阶迎风格式.湍流模型为Baldwin-Barth一方程模型.一无弯度薄翼的数值计算结果表明本文的数值方法是成功的.通过数值分析,揭示了弯度和展弦比对气动力特性的影响,也给出了不同弯度机翼流动结构的差别.