Gust response analysis and wind tunnel test for a high-aspect ratio wing

A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.

Aeroelastic Analysis and Optimization of High-aspect-ratio Composite Forward-swept Wings

In order to analyze the effects of forward-swept angle and skin ply-orientation on the static and dynamic aeroelastic characteristics, the aeroelastic modeling and calculation for high-aspect-ratio composite wings with different forward-swept angles and skin ply-orientation are performed. This paper presents the results of a design study aiming to optimize wings with typical forward-swept angles and skin ply-orientation in an aeroelastic way by using the genetic/sensitivity-based hybrid algorithm. Under the conditions of satiated multiple constraints including strength, displacements, divergence speeds and flutter speeds, the studies are carried out in a bid to minimize the structural weight of a wing with the lay-up thicknesses of wing components as design variabies. In addition, the effects of the power of spanwise variation function of lay-up thicknesses of skins and iugs on the optimized weights are also analyzed.

Structural Modeling and Aeroelastic Analysis of High-Aspect-Ratio Composite Wings

A unified structural model for high-aspect-ratio composite wing with arbitrary cross-section is developed. Two types of lay-ups of the composite wing, namely, circumferentially uniform stiffness （CUS） configuration and circumferentially asymmetric stiffness （CAS） configuration, are investigated. The present structural modeling method is validated through ANSYS FEM software for the case of a composite box beam. Then, the case of a single-cell composite wing with NACA0012 airfoil shape is considered. To investigate the aeroelastic problem of high-aspect-ratio composite wings, the linear ONERA aerodynamic model is used to model the unsteady aerodynamic loads under the case of small angle of attack. Finally, flutter speeds of the high-aspect-ratio wing with various composite ply angles are determined by using U-g method.

Stall Flutter Analysis of High-Aspect-Ratio Composite Wing

The stall flutter characters of high-aspect-ratio composite wing are investigated, and the effects of structure geometric nonlinearity and stiffness couple created by composite anisotropy on them also are discussed. Firstly, the high-aspect-ratio wing is modeled as a composite thin-walled closed section Euler beam whose displacement and rotation both could be of finite value, and the nonlinear dynamic equations is build up on it with all the effects of geometric nonlinearity, aerodynamic nonlinearity and anisotropy of material being considered. Then vibration equations are deduced through perturbing the dynamic equations at wing＇s equilibrium position, and coupled with unsteady stall aerodynamic model and ONERA model, to obtain the nonlinear stall flutter analysis equations of wing. Finally, the flutter stabilities with various wind speeds are determined by the harmonic balance method. With several exampies, the validity of the stall flutter model is proved, and the significant effects of geometric nonlinearity on the stall flutter various characters as wall as the effects of ply angle on the stall flutter speed and frequency also are discussed.

Stiffness Distribution and Aeroelastic Performance Optimization of High-Aspect-Ratio Wings

The relationship between stiffness distribution and aeroelastic performance for a beam-frame model and a3-D model is investigated based on aeroelastic optimization of global stiffness design for high-aspect-ratio wings.The sensitivity information of wing spanwise stiffness distribution with respect to the twist angle at wing tip,the vertical displacement at wing tip,and the flutter speed are obtained using a sensitivity method for both models.Then the relationship between stiffness distribution and aeroelastic performance is summarized to guide the design procedure.By using the genetic/sensitivity-based hybrid algorithm,an optimal solution satisfying the strength,aeroelastic and manufacturing constraints is obtained.It is found that the summarized guidance is well consistent with the optimal solution,thus providing a valuable design advice with efficiency.The study also shows that the aeroelastic-optimization-based global stiffness design procedure can obtain the optimal solution under multiple constraints with high efficiency and precision,thereby having a strong application value in engineering.

Effects of aspect ratio on flapping wing aerodynamics in animal flight

Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios（AR）of1,2,and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated.Flow structures on sectional cuts along the wing span are compared.Stronger K-H instability is found on the leading edge vortex of wings with higher aspect ratios.Vortex bursting only appears on the outer spanwise locations of high-aspect-ratio wings.The vortex bursting on high-aspect-ratio wings is perhaps one of the reasons why bio-flyers normally have low-aspect-ratio wings.Quantitative analysis exhibits larger dimensionless circulation of the leading edge vortex（LEV）over higher aspect ratio wings except when vortex bursting happens.The average dimensionless circulation of AR1 and AR2 along the span almost equals the dimensionless circulation at the 50%span.The flow structure and the circulation analysis show that the sinusoidal kinematics suppresses breakdown of the LEV compared with simplified flapping kinematics used in similar studies.The Reynolds number effect results on AR4 show that in the current Re range,the overall flow structure is not sensitive to Reynolds number.

Measurement of Vibrational Stiffness and Air Damping of Damselfly Wings

A simple cantilever beam vibration test method made of biomorph and insect wing, were used to measure the vibrational stiffness and the air damping of insect wings. Vibration tests were performed in vacuum pressures to atmosphere and the wing stiffness and air damping factor were measured. The test method was found to be a viable method for measuring wing stiffness, natural frequencies and mode shapes. The vibrational deformation of the insect wings was found to be combination of bending and torsion because of unsymmetrical geometry of wing. The measured stiffness (K) of damselfly wings varied from 0.18 to 0.31 N/m and the air damping ratio ranged from 0.72 to 0.79. The undamped natural frequency (fn) at 13 kPa varied from 249 to 299 Hz and at atmosphere it varied from 168 to 198 Hz.

Improvement of Artificial Foldable Wing Models by Mimicking the Unfolding/Folding Mechanism of a Beetle Hind Wing

In an attempt to realize a flapping wing micro-air vehicle with morphing wings, we report on improvements to our previousfoldable artificial hind wing.Multiple hinges, which were implemented to mimic the bending zone of a beetle hind wing, weremade of small composite hinge plates and tiny aluminum rivets.The buck-tails of rivets were flared after the hinge plates wereassembled with the rivets so that the folding/unfolding motions could be completed in less time, and the straight shape of theartificial hind wing could be maintained after fabrication.Folding and unfolding actions were triggered by electrically-activatedShape Memory Alloy (SMA) wires.For wing folding, the actuation characteristics of the SMA wire actuator were modifiedthrough heat treatment.Through a series of flapping tests, we confirmed that the artificial wings did not fold back and arbitrarilyfluctuate during the flapping motion.

Use of a Digital Image Correlation Technique for Measuring the Material Properties of Beetle Wing

Beetle wings are very specialized flight organs consisting of the veins and membranes.Therefore it is necessary from a bionic view to investigate the material properties of a beetle wing experimentally.In the present study,we have used a Digital Image Correlation (DIC) technique to measure the elastic modulus of a beetle wing membrane.Specimens were prepared by carefully cutting a beetle hind wing into 3.0 mm by 7.0 mm segments (the gage length was 5 mm).We used a scanning electron microscope for a precise measurement of the thickness of the beetle wing membrane.The specimen was attached to a designed fixture to induce a uniform displacement by means of a micromanipulator.We used an ARAMISTM system based on the digital image correlation technique to measure the corresponding displacement of a specimen.The thickness of the beetle wing varied at different points of the membrane.The elastic modulus differed in relation to the membrane arrangement showing a structural anisotropy;the elastic modulus in the chordwise direction is approximately 2.65 GPa,which is three times larger than the elastic modulus in the spanwise direction of 0.84 GPa.As a result,the digital image correlation-based ARAMIS system was suc- cessfully used to measure the elastic modulus of a beetle wing.In addition to membrane's elastic modulus,we considered the Poisson's ratio of the membrane and measured the elastic modulus of a vein using an Instron universal tensile machine.The result reveals the Poisson's ratio is nearly zero and the elastic modulus of a vein is about 11 GPa.

Piezoelectric energy harvesting from flexible delta wings

The potential for harvesting energy from a flexible delta wing using a piezoelectric bimorph is experimentally investigated.Different configurations of the proposed harvesting system were tested in a wind tunnel over a broad range of airspeeds.In addition to evaluating the level of harvested power,an analysis is performed to extract critical aspects for the relation between speed,flexibility,geometry and the potential power that can be harvested from a clamped,cantilevered flexible delta wing at low angles of attack and low speeds.This analysis provides an insight into parameters that impact energy harvesting from flexible membranes or elements.

大展弦比飞行器变形辅助高度控制策略

针对变形飞行器结构/飞行耦合动力学的飞行控制问题,以大展弦比飞行器为研究对象开展了变形辅助高度控制策略研究。采用单元翼多体假设,构建了大展弦比飞行器二面角变形结构,建立了结构/飞行纵向耦合动力学模型,基于线性二次型(LQR)控制器设计方法设计了主动变形(AM)和被动变形(PM) 2种控制策略。其中,被动变形控制策略仅采用升降舵作为控制输入,结构二面角动态行为由耦合动力学驱动;主动变形控制策略以二面角铰链处的扭矩作为额外输入对高度跟踪进行协调控制。仿真分析了2种控制策略下的高度跟踪效果及状态变化,研究结果表明:采用主动变形控制策略可有效改善高度跟踪暂态过程的性能,降低姿态回路的阻尼特性,为未来先进变形飞行器的结构/飞行一体化控制提供研究基础。

Experimental Study on the Effect of Increased Downstroke Duration for an FWAV with Morphing-coupled Wing Flapping Configuration

This paper is based on a previously developed bio-inspired Flapping Wing Aerial Vehicle(FWAV),RoboFalcon,which can fly with a morphing-coupled flapping pattern.In this paper,a simple flapping stroke control system based on Hall effect sensors is designed and applied,which is capable of assigning different up-and down-stroke speeds for the RoboFalcon platform to achieve an adjustable downstroke ratio.The aerodynamic and power characteristics of the morphing-coupled flapping pattern and the conventional flapping pattern with varying downstroke ratios are measured through a wind tunnel experiment,and the corresponding aerodynamic models are developed and analyzed by the nonlinear least squares method.The relatively low power consumption of the slow-downstroke mode of this vehicle is verified through outdoor flight tests.The results of wind tunnel experiments and flight tests indicate that increased downstroke duration can improve aerodynamic and power performance for the RoboFalcon platform.

大展弦比机翼随动加载方法与装置研究

大展弦比机翼载荷标定实验中,随着载荷的增加,机翼会发生弯曲变形,导致加载点的法向载荷方向发生变化,对载荷标定实验的准确性产生影响。为解决此问题,设计了一套大展弦比随动加载装置,该装置通过电缸控制加载点竖直方向的位移,通过位移台控制电缸水平方向的位移,利用联动控制系统使载荷标定实验中施加在机翼翼面的作用力与翼面始终保持垂直,保证机翼所受载荷始终沿法向。开展随动加载与砝码垂向加载对比实验,结果表明:随动加载获得的数据相关系数达到0.999,相较砝码垂向加载获得的数据相关系数0.976更优,验证了随动加载装置的有效性。该装置不仅具有体积较小、操作简便的优点,还为推动大展弦比机翼性能研究提供了有力支撑。

大长径比变后掠翼导弹的颤振特性分析

为了增大导弹的内部空间,同时减小空气阻力,导弹外形日益趋于大长径比机构,而这样的设计易造成导弹低频颤振等明显的气动弹性问题。为解决上述问题,可通过调节导弹的气动外形,改变系统气动特性,达到抑制颤振的作用。针对变体飞行器技术之一的变后掠翼展开研究,围绕大长径比导弹的颤振问题,揭示飞行速度对导弹飞行时颤振特性的影响规律,而后验证通过改变导弹后掠角主动抑制导弹颤振方法的可行性,为解决导弹的颤振问题提供理论支撑。

升力翼对高速列车通过隧道时气动效应的影响

在高速列车上安装升力翼可以为高速列车提供升力,降低列车对轨道的压力,从而有效减少轮轨磨损,但安装升力翼对列车在隧道内行驶时的气动性能产生较大影响,为此,基于三维非定常可压缩RNG k−ε两方程湍流模型,对升力翼列车通过隧道时的气动效应进行数值模拟研究。研究结果表明:在列车进入隧道过程中,升力翼尾流结构增大,对列车表面压力产生一定的影响;升力翼尾流使列车表面压力下降,同时升力翼增加车隧阻塞比,使列车表面的压力上升,两者共同影响列车表面压力,导致列车表面压力分布复杂;安装升力翼使列车表面与隧道壁面的压力幅值均增加,列车表面压力幅值最大增加5.4%,隧道壁面压力幅值最大增加14.1%;同时,对隧道出口的微气压波产生不利影响,在距离隧道出口20 m处的微气压波幅值上升4.1%。研究结果可为升力翼的参数优化设计提供指导。

铺层参数对大展弦比复合材料机翼气动弹性的影响研究

采用偶极子格网法计算非定常气动力,利用P-K法计算颤振速度,对大展弦比复合材料机翼的颤振特性进行研究,重点探讨非均衡系数铺层、等厚度多角度铺层和同角度变厚度铺层对颤振速度和高亚音速凹坑现象的影响。研究表明:相比0°铺层角度,±45°铺层角度可以较大幅度提升颤振速度并减小凹坑的区域,获得更大的飞行马赫数和动稳定性;在低亚音速中,与非均衡铺层相比,均衡铺层的颤振速度更高,颤振速度对非均衡系数的影响并不显著;在高亚音速中,均衡铺层可以提升最低点的颤振速度,减小凹坑的深度,而非均衡铺层可以滞后最低点的颤振速度;铺层厚度的增加可以提高颤振速度,且二者呈线性关系,但随着铺层厚度的提升,固有频率降低。

展弦比对NACA0012弹性平直机翼颤振临界特性影响研究

展弦比是飞行器机翼设计的重要参数,研究其对机翼颤振临界特性的影响具有重要的工程应用价值。本文采用三维雷诺平均N-S方程和S-A湍流模型求解NACA0012弹性平直机翼的非定常气动力,结合由模态法建立的机翼结构动力学方程,发展了计算流体力学(CFD)/计算结构力学(CSD)颤振时域数值模拟方法。利用该方法研究了不同展弦比条件下机翼的颤振临界速度和频率。结果表明,由于展弦比较大且材质轻柔,机翼会出现一定幅度的垂向静弯曲变形。展弦比的增大不会影响机翼模态固有振型,但是会导致机翼颤振临界速度、颤振频率和模态固有频率的降低。

翼身融合飞翼式水下滑翔机的水动力性能研究

本文依据翼身融合式飞行器的设计理念设计一种飞翼式水下滑翔机,及其主要设计参数。通过计算发现该飞翼式水下滑翔机较传统水下滑翔机拥有更大的升阻比,可达到15以上。流场分布结果显示飞翼式水下滑翔机在特定速度0.1 m/s、0.3 m/s和0.5 m/s下,机翼周围并未出现明显的流动分离,且机翼表面压力较大程度取决于攻角的大小。对比了不同雷诺数下的机翼表面涡脱落情况,发现随着攻角增大涡的脱落急剧增多,且翼梢小翼尾部涡脱落最为严重,极大影响滑翔机的水动力特性。

某型气象探测火箭的气动力3维数值模拟

针对气象探测火箭载荷轻、速度高的特点,对气象探测火箭进行气动力3维数值模拟。以某型小口径大长径比气象探测火箭弹为基础,进行全弹建模与计算,分析其在跨音速情况下的气动力特性,验证了该种大展弦比刀形尾翼在小口径大长径比跨音速气象探测火箭弹上的可行性。结果表明,该分析可为小口径大长径比火箭弹的尾翼设计提供参考。

基于Fluent与Fensap-ice的AIAAC仿真

无人机机翼结冰严重限制了其操控性。基于Fluent与Fensap ice的数值模拟方法对某无人机机翼结冰过程进行耦合仿真计算,研究了结冰时长、飞行速度、MVD、LWC等结冰参数对翼型结冰过程的影响,并基于结冰后的二维翼型表面对其气动性能进行分析,发现随着结冰时长的增大、飞行速度的增加、MVD(水滴平均直径)与LWC(云层液态水含量)等参数的增大,飞机结冰对其气动特性的影响越来越恶劣,但结冰大小、气动性能变化程度与产生变化的原因不同。通过分析结冰前后的气动性能变化,可为不同环境下结冰状态选取以及防除冰装置的设计提供指导。