IMPROVED UVLM FOR FLAPPING-WING AERODYNAMICS COMPUTATION

To calculate the aerodynamics of flapping-wing micro air vehicle（MAV） with the high efficiency and the engineering-oriented accuracy,an improved unsteady vortex lattice method （UVLM） for MAV is proposed. The method considers the influence of instantaneous wing deforming in flapping,as well as the induced drag,additionally models the stretching and the dissipation of vortex rings,and can present the aerodynamics status on the wing surface. An implementation of the method is developed. Moreover,the results and the efficiency of the proposed method are verified by CFD methods. Considering the less time cost of UVLM,for application of UVLM in the MAV optimization,the influence of wake vortex ignoring time saving and precision is studied. Results show that saving in CPU time with wake vortex ignoring the appropriate distance is considerable while the precision is not significantly reduced. It indicates the potential value of UVLM in the optimization of MAV design.

具有较大折展比的仿生可展机构的折叠特性分析

甲虫飞行的运动学特性不仅可以指导扑翼微型飞行器的设计,其后翅柔顺的折叠机理有利于设计大折展比的仿生可展刚性折展机构。文中基于甲虫后翅的折痕图案和折叠线的分布特性构造仿生等效折纸模型,分析了其刚性和可折叠性。设计了由四边形板和铰链构成并具有单自由度的可折叠太阳能板。然后使用ADAMS软件数值模拟可展机构的运动特性,确定了所设计模型的可展能力。所提出的仿生可展机构具有广泛的通用性,可以应用于可变翼机器人的翅翼优化设计。

微扑翼飞行器的尺度律研究与仿生设计

通过分析飞行动物扑翼飞行中的各种物理参量对飞行特性的影响,得出了能为微扑翼飞行器设计所利用的规律。根据几何相似原理,利用基于量纲的尺度分析从本质上揭示了扑翼飞行中各种物理参量之间的相互联系。分析发现,几何尺度对微扑翼飞行器在翼展、翼面积、翼载荷、展弦比和扑翼频率等总体设计参数的影响趋势和对飞行动物相应物理量的影响趋势一致,但在具体量值上有所差异。根据扑翼飞行动物统计分析得到的尺度律设计并制作出了实际可飞的微扑翼飞行器。

仿生飞行器非定常气动优化设计研究进展与挑战

从气动建模、设计变量参数化和优化方法策略等方面,论述了仿生飞行器非定常气动优化设计技术的应用和发展,总结了不同优化设计方法的优缺点,分析了发展趋势和未来的研究重点,为进一步开展仿生飞行器气动优化设计研究提供参考。

某仿蝉翅膀气动功率特性的分析

针对某一特定形状仿蝉微飞行器的翅膀,进行了瞬时功率特性以及平均功率特性的分析.通过仿真,分析了翅膀在3种典型转动模式下的瞬时功率特性、平均功率与攻角幅值的关系,以及最大功率-平均功率比值与攻角幅值之间的关系.结果表明,该型翅膀超前模式下的平均转动气动功率对攻角幅值的变化比较敏感;滞后模式下转动气动功率最大峰值-平均值的比值对攻角幅值的变化也比较敏感;而平均拍动气动功率和攻角幅值之间的关系可近似地认为与模式无关;拍动气动功率最大峰值-平均值的比值和攻角幅值之间的关系也可近似地认为与模式无关.

仿蝉翅膀气动力及扭矩特性的分析

为仿蝉微飞行器(MAV)设计了一款翅展33 mm的翅膀,并采用准静态模型对该翅膀的气动力及扭矩特性进行了仿真分析;同时还分析了以上特性与攻角幅度之间的关系.力特性仿真结果表明,在超前模式典型拍动参数下,一对翅膀能提供26 g左右的平均升力,足于平衡质量为十几克的仿蝉微飞行器;同时提供合适的剩余升力供机动.扭矩仿真结果表明,翅膀转动模式对转动扭矩的影响很大,而对拍动扭矩影响较小;攻角幅值对转动和拍动扭矩的影响均比较大,但是超前模式下的转动扭矩却几乎不受攻角幅值的影响.为检验仿真结果的可信度,与相关文献类似实验的测量数据进行了比较.结果表明,仿真所得气动力曲线与相比较的实验结果曲线形状相似,特征点位置和幅度吻合较好.

仿生微型扑翼飞行器飞行性能计算与分析

仿生微型扑翼飞行器是近年来国内外的研究热点,飞行性能计算是飞行器总体设计过程中的重要步骤。首先分析了扑翼飞行器与常规固定翼飞行器在性能估算方法方面的不同之处,基于扑翼气动计算与风洞实验测量的结果,提出了扑翼飞行器性能计算方法,并对所研制的扑翼飞行器的平飞性能、爬升性能、续航性能进行了计算与分析。扑翼的频率在一定程度上代表油门,而频率和升力、推力均是耦合的关系。计算结果表明,在一定频率下,可能存在2种稳定巡航状态,一种是小迎角大速度,一种是大迎角小速度,两者对应不同的功耗。根据飞行器的参数可以计算出上升性能和续航性能,扑翼飞行器的速度功率特性曲线为U字形,通过作图法可求得曲线的最小斜率为远航速度,U形曲线的速度最小值为久航速度。该飞行性能计算方法可用于评估仿生扑翼飞行器的飞行能力。

微型飞行器的低雷诺数、非定常气动设计与分析

低雷诺数和非定常气动特性是微型飞行器有别于常规飞行器的主要特点。首先简要介绍了飞行雷诺数的含义,并从低雷诺数的附面层特性和其对气动力的影响两方面分析了雷诺数对气动特性的影响,并给出了两种低雷诺数微型飞行器的空气动力学计算方法。接着分析了固定翼、旋翼、扑翼三类微型飞行器的非定常运动特征,重点介绍了仿生扑翼微型飞行器的非定常运动及其实现途径。然后介绍了旋翼气动力简化计算方法、非定常空气动力计算的N-S方程数值方法,并给出了低雷诺数非定常气动设计软件和应用案例。最后,提出将人工智能的方法引入微型飞行器控制系统势在必行,这将是飞行器自主感知,最终解决控制问题的重要途径。

Bird-mimetic Wing System of Flapping-wing Micro Air Vehicle with Autonomous Flight Control Capability

A micro air vehicle with a bird-mimetic up-down and twisting wing drive system was developed in this study. The Flap- ping-wing Micro Air Vehicle （FMAV）, with a 50 cm wingspan and a double-crank drive system, performed successful flights of up to 23 min. The performance and capabilities of the FMAV were enhanced by adapting a number of unique features, such as a bird-mimetic wing shape with a span-wise camber and an up-down and twisting wing drive mechanism with double-crank linkages, This lift-enhancing design by mimicking the flapping mechanism of a bird＇s wing enabled the 210 g FMAV to fly autonomously in an outdoor field under wind speeds of less than 5 m.s-1. Autonomous flight was enabled by installing a flight control computer with a micro-electro-mechanical gyroscope and accelerometers, along with a micro video camera and an ultralight wireless communication system inside the fuselage. A comprehensive wind tunnel test shows that the FMAV with a high-camber wing and double-crank mechanism generates more lift and less net thrust than the FMAV with a flat wing and single-crank mechanism, which confirms the improved performance of the developed FMAV, as well as the superior slow flying or hovering capabilities of the FMAV with a high-camber wing and double-crank wing drive system.

Effect of Wing Kinematics Modulation on Aerodynamic Force Generation in Hovering Insect-mimicking Flapping-wing Micro Air Vehicle

We investigated the effect of wing kinematics modulation, which was achieved by adjusting the location of trailing-edge constraint at the wing-root, i.e., by adjusting the wing-root offset, on the generation of aerodynamic forces in a hovering in- sect-mimicking Flapping-Wing Micro Air Vehicle （FW-MAV） by numerical and experimental studies. Three-dimensional wing kinematics measured using three synchronized high-speed cameras revealed a clear difference in the wing rotation angle of a wing section for different wing-root offsets. The extrapolated wing kinematics were in good agreement with the measured ones for various wing-root offsets. The Unsteady Blade Element Theory （UBET） was used to estimate the forces generated by the flapping wings and validated by comparison with results of measurements performed using a load cell. Although the thrust produced by a flapping wing with a wing-root offset of 0.20 c was about 4% less, its force-to-input-power ratio was about 30% and 10% higher than those with the offsets of 0.10 c and 0.15 c, respectively. This result could be explained by analyzing the effective Angle of Attack （AoA） and the force components computed by the UBET. Thus, a flapping wing with a wing-root offset of 0.20 c can be regarded as an optimal twist configuration for the development of the FW-MAV.

HIT-Hawk and HIT-Phoenix: Two kinds of flapping-wing flying robotic birds with wingspans beyond 2 meters

Inspired by large and medium-sized birds,two kinds of flapping-wing flying robots with wingspans beyond 2 meters were developed.They have the appearance of a hawk and a phoenix respectively,so they are called HIT-Hawk and HIT-Phoenix.In this paper,the bionic concept,theoretical analysis,design and manufacturing are introduced in detail.Firstly,the flight principle and characteristics of large and medium-sized birds were summarized.Then,the aerodynamics was modeled based on the thin airfoil theory,and the main design basis was established.Secondly,the mechanical structures of HIT-Hawk and HIT-Phoenix were designed to ensure the lateral and longitudinal stability and have optimized flight performance.Moreover,an autonomous flight control method was proposed and realized in highly integrated on-onboard controller;it satisfies the strict restrictions on mass,size,power and shape.Finally,the prototypes were fabricated and verified through practical flight experiments.The wingspans of these two flapping wing aircrafts are 2.0 m and 2.3 m respectively,the take-off weights are 1.15 kg and 0.86 kg,and the maximum stable endurance is 65 min(with battery of 3S LiPo,4300 mAh)and 8 min(with battery of 3S LiPo,800 mAh).Their wind resistance can both reach level 4.Compared with the small and micro flapping-wing aerial vehicles that mimic insects or small birds,they both have strong load capacity,strong wind resistance and long endurance.

Autonomous Formation Flight Control of Large-Sized Flapping-Wing Flying Robots Based on Leader–Follower Strategy

Birds in nature exhibit excellent long-distance flight capabilities through formation flight,which could reduce energy consumption and improve flight efficiency.Inspired by the biological habits of birds,this paper proposes an autonomous formation flight control method for Large-sized Flapping-Wing Flying Robots(LFWFRs),which can enhance their search range and flight efficiency.First,the kinematics model for LFWFRs is established.Then,an autonomous flight controller based on this model is designed,which has multiple flight control modes,including attitude stabilization,course keeping,hovering,and so on.Second,a formation flight control method is proposed based on the leader–follower strategy and periodic characteristics of flapping-wing flight.The up and down fluctuation of the fuselage of each LFWFR during wing flapping is considered in the control algorithm to keep the relative distance,which overcomes the trajectory divergence caused by sensor delay and fuselage fluctuation.Third,typical formation flight modes are realized,including straight formation,circular formation,and switching formation.Finally,the outdoor formation flight experiment is carried out,and the proposed autonomous formation flight control method is verified in real environment.

Study on the Vibration Reduction Characteristics of FWMAV Flexible Bionic Wings Mimicking the Hindwings of Trypoxylus dichotomus

Using the method of structural finite element topology optimization and analysis of the hindwings of Trypoxylus dichotomus,this work identified the main loading force transmission path and designed the initial structure of a bionic flexible wing.A structural design scheme of the vibration damping unit was proposed,and the structural mechanics and modal vibration characteristics were simulated and analyzed.3D printing technology was used to manufacture the designed bionic wing skeleton,which was combined with two kinds of wing membrane materials.The Flapping Wing Micro-aerial Vehicle(FWMAV)transmission mechanism vibration characteristics were observed and analyzed by a high-speed digital camera.A triaxial force transducer was used to record the force vibration of the flexible bionic wing flapping in a wind tunnel.A wavelet processing method was used to process and analyze the force signal.The results showed that the force amplitude was more stable,the waveform roughness was the lowest,and the peak shaving phenomenon at the z-axis was the least obvious for the bionic flexible wing model that combined the topology-optimized bionic wing skeleton with a polyamide elastic membrane.This was determined to be the most suitable design scheme for the wings of FWMAVs.

仿昆虫扑翼微飞行器研究现状与关键技术

仿昆虫扑翼微飞行器基于对自然界中各类昆虫扑翼飞行机理的仿生,具有尺寸微小、隐蔽性高、灵活机动等优势。依据仿昆虫扑翼微飞行器所普遍采用的静电驱动、压电驱动、电机驱动、电磁驱动和其他驱动等扑翼驱动方式,依次分类介绍并总结目前仿昆虫扑翼微飞行器的发展历程、国内外研究现状和最新进展。同时针对目前仿昆虫扑翼微飞行器所采用的各类驱动方式、飞行方式、控制方案、胸腔机构设计、整机系统共振机制以及机载设备搭载研究等关键技术进行了分析和总结。

Extended State Observer based Attitude Control of a Bird-like Flapping-wing Flying Robot

The attitude control system of a flapping-wing flying robot plays an important role in the precise orientation and tracking of the robot.In this paper,the modeling of a bird-like micro flapping-wing system is introduced,and the design of a sliding mode controller based on an Extended State Observer(ESO)is described.The main design difficulties are the control law and the adaptive law for the attitude control system.To address this problem,a sliding mode adaptive extended state observer algorithm is proposed.Firstly,a new extended state approximation method is used to estimate the final output as a disturbance state.Then,a sliding mode observer with good robustness to the model approximation error and external disturbance is used to estimate the system state.Compared with traditional algorithms,this method is not only suitable for more general cases,but also effectively reduces the influence of the approximation error and interference.Next,the simulation and experiment example is given to illustrate the implementation process.The results show that the algorithm can effectively estimate the state of the attitude control system of the flapping-wing flying robot,and further guarantee the robustness of the model regarding error and external disturbance.

甲虫后翅及其FWMAV可折叠翼仿生研究

对将甲虫后翅的研究应用于FWMAV仿生可折叠翼研制的前沿交叉领域进行了综合评述,并对其未来研究进行了展望。首先分析了甲虫后翅结构及其材料力学性能;其次讨论了后翅结构对其静力学和动力学性能的影响;然后概括了基于甲虫后翅建立的仿生翼及其力学特性研究现状;最后对仿生可折叠翼力学性能的研究做出了总结并对其重点研究方向给出建议。综述表明:甲虫后翅的不同单元具有各异的力学性能,其不同结构可影响静力学和动力学特性;依据后翅制造的可折叠柔性翼具有明显的尺寸优势,既有助于双翼产生高升力,又可抵抗部分耦合冲击以提高飞行稳定性。未来以甲虫后翅为仿生原型研制适用于FWMAV的可折叠柔性翼,应着眼于柔性翼骨架结构和机翼翼膜材料属性的各向异性,以期制造出可折叠、易扭转、高弹性的微飞行器机翼。

柔性翼微型飞行器的稳定特性

为提高微型飞行器(M AV)的抗风扰动飞行稳定性,需要遵循仿生学原理,效仿自然界中的鸟类和昆虫,探讨抗风飞行的新方法。提出了柔性仿生机翼的概念,阐述了其设计思想与工作原理,并导出了大气扰动下柔性机翼气动力的解析表达。为验证柔性仿生机翼的实际性能,设计和制作了柔性仿生机翼M AV原理样机,并在风中进行了飞行试验。试验结果表明:采用柔性机翼能够显著改善有风条件下M AV的飞行品质,突风过载可降低40%左右,大大减弱了大气扰动对飞行的影响,有效提高了M AV的飞行稳定性。

扑旋翼刚度和翼梢形状对气动升力和效率的影响

具有垂直起降及悬停性能的扑旋翼刚度分布和形状对其气动升力和效率的影响与传统仿昆虫扑翼明显不同。针对扑旋翼刚度和翼梢形状对其悬停飞行模式下的气动升力和效率的影响开展实验研究,研制了12种不同结构构型及翼梢后掠角的传统矩形扑旋翼样件和一种仿蜻蜓翅外形的扑旋翼样件,通过实验测试定量分析了各扑旋翼样件的展向和弦向刚度、翼梢刚度及形状对其运动、气动升力和效率的影响。结果表明,弦向刚度和翼梢形状对扑旋翼运动影响显著,优化展向和弦向刚度分布对翼膜的支撑和采用仿蜻蜓翅梢形状可显著提高扑旋翼的气动升力和效率。以本实验中采用的重量为30.1 g的扑旋翼模型为例,在输入电压3.4 V时,优化后的仿生扑旋翼平均升力(49.6 g)比初始矩形扑旋翼提高74%,升力效率从3.5 g/W提高到5.9 g/W。本研究对扑旋翼微型飞行器气动性能的提升具有重要意义。

可悬停扑翼飞行器研究现状与关键技术

可悬停扑翼飞行器模仿自然界定点滞空昆虫和鸟类的飞行特点,隐蔽性高、灵活机动、应用环境多样,具有突出的理论和实用价值,引起了世界范围的广泛关注。对可悬停扑翼飞行器的研究现状和发展方向进行了综合评述。首先总结了近年来最突出的研究成果,按照微扑翼尺寸分类分别介绍MAV、NAV、PAV尺度下可悬停扑翼微飞行器的样机构型、动力系统、质量分配与飞行性能,统计了升力、翼展、质量、扑翼幅值等重要参数,介绍了电机、压电和电磁驱动扑翼微飞行器最具代表性的研究工作;然后针对目前飞行器研究运用的升力产生原理、飞行稳定性分析、功耗效率优化、续航能力等关键技术进行了分析和总结;最后讨论了扑翼飞行器亟待突破的技术难题和未来发展方向。

Wing Modulation and Aerodynamics of Hoverflies in Gust Perturbations

Flapping-Wing Micro-Air Vehicles are likely to suffer from airflow perturbations.They can mimic the wing modulation of insects in airflow perturbations.However,our knowledge of wing modulation of insects to airflow perturbations remains limited.Here,we subjected hoverflies to headwind and lateral gust perturbations and filmed their wing motions.Then,computational fluid dynamics was employed to estimate the effects of hoverflies’wing kinematic modulations.We also clipped off the antennae of hoverflies to test whether the wing kinematic modulations were different.Results show that hoverflies increase the mean positional angle and modulate the deviation angle to make the wing tip paths of upstroke and downstroke close to compensate for the pitch moment perturbations in the headwind gust.Hoverflies employ asymmetric responses in positional angle in the lateral gust.The stroke amplitude of the left(right)wing increases(decreases)and the mean positional angle of the left(right)wing decreases(increases)during the right lateral gust.Antennae have little effect on the wing kinematic modulations in the lateral gust.These asymmetric responses produce a roll moment,tilting the body to resist the side force generated by the gust.This is a typical helicopter model employed by hoverflies to alleviate the gust.These results provide insight into the remarkable capacity of hoverflies to contend with gusts and can also inspire the design of flapping-wing micro-air vehicles.