Computational aerodynamic analysis on perimeter reinforced （PR）-compliant wing

Abstract Implementing the morphing technique on a micro air vehicle （MAV） wing is a very chal- lenging task, due to the MAWs wing size limitation and the complex morphing mechanism. As a result, understanding aerodynamic characteristics and flow configurations, subject to wing structure deformation of a morphing wing MAV has remained obstructed. Thus, this paper presents the investigation of structural deformation, aerodynamics performance and flow formation on a pro- posed twist morphing MAV wing design named perimeter reinforced （PR）-compliant wing. The numerical simulation of two-way fluid structure interaction （FSI） investigation consist of a quasi- static aeroelastic structural analysis coupled with 3D incompressible Reynolds-averaged Navier- Stokes and shear-stress-transport （RANS-SST） solver utilized throughout this study. Verification of numerical method on a rigid rectangular wing achieves a good correlation with available exper- imental results. A comparative aeroelastic study between PR-compliant to PR and rigid wing per- formance is organized to elucidate the morphing wing performances. Structural deformation results show that PR-compliant wing is able to alter the wing＇s geometric twist characteristic, which has directly influenced both the overall aerodynamic performance and flow structure behavior. Despite the superior lift performance result, PR-compliant wing also suffers from massive drag penalty, which has consequently affected the wing efficiency in general. Based on vortices investigation, the results reveal the connection between these aerodynamic performances with vortices formation on PR-comoliant wing.     

Experimental investigations of a full model with adaptive elasto-flexible membrane wings

The morphing wing concept aims to constantly adapt the aerodynamics to different flight stages. The wing is able to adapt to different flight conditions by an adjustable Aspect Ratio (AR) and sweep. A high AR configuration provides high aerodynamic efficiency, while a low AR configuration, with highly swept wings offers a good maneuverability. Additionally, the flexible membrane allows the wing surface to stretch and contract in-plane as well as the airfoil to adapt to different aerodynamic loads. In the context of this work, the aerodynamic characteristics of a full model with form-adaptive elasto-flexible membrane wings are investigated experimentally. The focus is on the high-lift regime and on the analysis of the aerodynamic coefficients as well as their sensitivities. Especially, the lateral aerodynamic derivatives at asymmetric wing positions are of interest.     

飞翼布局无人机变形机翼设计与模型验证研究

对飞翼布局无人机变形机翼和变形机翼传动机构进行了设计,根据设计结果制作验证模型进行风洞实验和外场飞行试验,以此研究伸缩段机翼对飞行器机翼整体气动性能的影响。结果表明:采用变形机翼技术,可以通过实时控制机翼的气动外形保持较高的气动效率,提高飞机在巡航状态下的升力和高速飞行状态下的机动性,满足飞机在各种任务剖面的战术性能要求。     

高性能无人机翼型的杂交优化设计

 发展了用于高性能无人机翼型设计的杂交优化设计方法。针对“类全球鹰”翼型的算例表明，该方法能满足低速时高升力（C_L）和跨声速巡航时高气动效率（C_L/C_D）两方面要求。优化翼型较初始翼型，其低速时的设计升力系数提高了19.80%，跨声速巡航时的设计升阻比提高了37.45%，并且在较大的速度区间内优化翼型都具有良好的综合性能。杂交优化设计方法可为高空长航时无人机的设计提供参考。     

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.     

多段柔性变体扑翼飞行器设计

多段柔性变体扑翼模仿海鸥翅膀的复杂运动.观察海鸥翅膀的运动周期,设计了包含慢频率扑动、展向折弯、弦向扭转和结构柔性变形的扑翼模型,并应用准定常方法计算气动力,为该扑翼飞行器设计提供依据.在CATIA和3DMAX中设计多段柔性变体扑翼机的三维模型和运动模拟,制作样机进行飞行试验,研究其平飞、爬升、偏航等飞行姿态,结果表明升力和推力与数值计算结果吻合.相较于原有扑翼飞行器,多段柔性变体扑翼飞行器可以慢频率扑动飞行,调整扑翼形状.      

折叠翼变体飞行器非定常气动特性实验研究

折叠翼变体飞行器是一种可以在飞行中改变自身气动外形的新型飞行器。研制出了一种折叠翼变体飞行器的风洞实验模型,在风洞实验中测得了模型不同变体位置下的气动力以及进行变体运动时气动力的动态变化过程,并通过PIV实验手段获得模型周围的流场在变体运动过程中的变化情况。结果表明：在机翼变形过程中,折叠翼模型有明显的非定常气动现象产生,而且折叠变形的速度越大,非定常现象越明显。出现非定常现象的主要原因是变体运动对机翼前缘涡的影响。     

Gain self-scheduled H_∞ control for morphing aircraft in the wing transition process based on an LPV model

This article investigates gain self-scheduled H 1 robust control system design for a tailless fold- ing-wing morphing aircraft in the wing shape varying process. During the wing morphing phase, the aircraft’s dynamic response will be governed by time-varying aerodynamic forces and moments. Nonlinear dynamic equations of the morphing aircraft are linearized by using Jacobian linearization approach, and a linear parameter varying (LPV) model of the morphing aircraft in wing folding is obtained. A multi-loop controller for the morphing aircraft is formulated to guarantee stability for the wing shape transition process. The proposed controller uses a set of inner-loop gains to provide stability using classical techniques, whereas a gain self-scheduled H 1 outer-loop controller is devised to guarantee a specific level of robust stability and performance for the time-varying dynamics. The closed-loop simulations show that speed and altitude vary slightly during the whole wing folding process, and they converge rapidly after the process ends. This proves that the gain self-scheduled H 1 robust controller can guarantee a satisfactory dynamic performance for the morphing aircraft during the whole wing shape transition process. Finally, the flight control system’s robustness for the wing folding process is verified according to uncertainties of the aerodynamic parameters in the nonlinear model.     

A study of morphing aircraft on morphing rules along trajectory

Morphing aircraft can meet requirements of multi-mission during the whole flight due to changing the aerodynamic shape, so it is necessary to study its morphing rules along the trajectory. However, trajectory planning considering morphing variables requires a huge number of expensive CFD computations due to the morphing in view of aerodynamic performance. Under the given missions and trajectory, to alleviate computational cost and improve trajectory-planning efficiency for morphing aircraft, an offline optimization method is proposed based on Multi-Fidelity Kriging (MFK) modeling. The angle of attack, Mach number, sweep angle and axial position of the morphing wing are defined as variables for generating training data for building the MFK models, in which many inviscid aerodynamic solutions are used as low-fidelity data, while the less high-fidelity data are obtained by solving viscous flow. Then the built MFK models of the lift, drag and pressure centre at the different angles of attack and Mach numbers are used to predict the aerodynamic performance of the morphing aircraft, which keeps the optimal sweep angle and axial position of the wing during trajectory planning. Hence, the morphing rules can be correspondingly acquired along the trajectory, as well as keep the aircraft with the best aerodynamic performance during the whole task. The trajectory planning of a morphing aircraft was performed with the optimal aerodynamic performance based on the MFK models, built by only using 240 low-fidelity data and 110 high-fidelity data. The results indicate that a complex trajectory can take advantage of morphing rules in keeping good aerodynamic performance, and the proposed method is more efficient than trajectory optimization by reducing 86% of the computing time.     

Aerodynamic characteristics of morphing wing with flexible leading-edge

The morphing wing can improve the flight performance during different phases. However, research has been subject to limitations in aerodynamic characteristics of the morphing wing with a flexible leading-edge. The computational fluid dynamic method and dynamic mesh were used to simulate the continuous morphing of the flexible leading-edge. After comparing the steady aerodynamic characteristics of morphing and conventional wings, this study examined the unsteady aerodynamic characteristics of morphing wings with upward and downward deflections of the leading-edge at different frequencies. The numerical results show that for the steady aerodynamic, the leading-edge deflection mainly affects the stall characteristic. The downward deflection of the leading-edge increases the stall angle of attack and nose-down pitching moment. The results are opposite for the upward deflection. For the unsteady aerodynamic, at a small angle of attack, the transient lift coefficient of the upward deflection, growing with the increase of deflection frequency, is larger than that of the static case. The transient lift coefficient of the downward deflection, decreasing with the increase of deflection frequency, is smaller than that of the static case. However, at a large angle of attack, an opposite effect of deflection frequency on the transient lift coefficient was demonstrated. The transient lift coefficient is larger than that of the static case when the leading edge is in the nose-up stage, and lower than that of the static one in the nose-down stage.     

Integrated optimization design of smart morphing wing for accurate shape control

Smart morphing wing, which is equipped with smart materials and able to change structural geometry adaptively, can further improve aerodynamic efficiency of aircraft. This paper presents a new integrated layout and topology optimization design for morphing wing driven by shape memory alloys (SMAs). By simultaneously optimizing the layout of smart actuators and topology of wing substrate, the ultimately determined configuration can achieve smooth, continuous and accurate geometric shape changes. In addition, aerodynamic analysis is carried out to compare smart morphing wing with traditional hinged airfoil. Finally, the optimized smart wing structure is constructed and tested to demonstrate and verify the morphing functionality. Application setbacks are also pointed out for further investigation.     

Efficient aerodynamic shape optimization using variable-fidelity surrogate models and multilevel computational grids

A variable-fidelity method can remarkably improve the efficiency of a design optimization based on a high-fidelity and expensive numerical simulation, with assistance of lower-fidelity and cheaper simulation(s). However, most existing works only incorporate “two” levels of fidelity, and thus efficiency improvement is very limited. In order to reduce the number of high-fidelity simulations as many as possible, there is a strong need to extend it to three or more fidelities. This article proposes a novel variable-fidelity optimization approach with application to aerodynamic design. Its key ingredient is the theory and algorithm of a Multi-level Hierarchical Kriging (MHK), which is referred to as a surrogate model that can incorporate simulation data with arbitrary levels of fidelity. The high-fidelity model is defined as a CFD simulation using a fine grid and the lower-fidelity models are defined as the same CFD model but with coarser grids, which are determined through a grid convergence study. First, sampling shapes are selected for each level of fidelity via technique of Design of Experiments (DoE). Then, CFD simulations are conducted and the output data of varying fidelity is used to build initial MHK models for objective (e.g. C_D) and constraint (e.g. C_L, C_m) functions. Next, new samples are selected through infill-sampling criteria and the surrogate models are repetitively updated until a global optimum is found. The proposed method is validated by analytical test cases and applied to aerodynamic shape optimization of a NACA0012 airfoil and an ONERA M6 wing in transonic flows. The results confirm that the proposed method can significantly improve the optimization efficiency and apparently outperforms the existing single-fidelity or two-level-fidelity method.     

Delaying stall of morphing wing by periodic trailing-edge deflection

Morphing wings can improve aircraft performance during different flight phases. Recently research has focused on steady aerodynamic characteristics of the morphing wing with a flexible trailing-edge, and the unsteady aerodynamic and stall characteristics in the deflection process of the morphing wing are worthy further investigation. The effects of the angle of attack and deflection rate on aerodynamic characteristics were examined, and based on the aerodynamic characteristics of the morphing wing, a method was developed to delay stall by using the flexible periodic trailing-edge deflection. The numerical results show that the lift coefficients in the deflection process are smaller than those in the static situation at small angles of attack, and that the higher the deflection rate is, the smaller the lift coefficients will be. On the contrary, at large angles of attack, the lift coefficients are higher than those in the static case, and they become larger with the increase of the deflection rate. Further, the periodic deflection of the flexible trailing-edge with a small deflection amplitude and high deflection rate can increase lift coefficients at the critical stall angle.     

翼尖连接机翼布局弹性气动力探讨

翼尖连接机翼(Joined Wing)布局将后掠的前翼和前掠的后翼在翼尖处用端板相连,后掠翼和前掠翼互相依存,克服平直机翼的局限,提高飞行临界M数,减小诱导阻力,抑制前掠翼的发散倾向.但是该布局的设计参数选择需要气动,结构强度,气动弹性等多学科综合分析,多学科设计优化还需要提供相对于气动设计参数的敏度.探讨了一种翼尖连接机翼布局包含发散速压和变形在内的刚性和弹性气动特性,以及对气动设计参数的敏度,可供该布局的多学科设计优化参考.     

Proportional fuzzy feed-forward architecture control validation by wind tunnel tests of a morphing wing

In aircraft wing design, engineers aim to provide the best possible aerodynamic performance under cruise flight conditions in terms of lift-to-drag ratio. Conventional control sur-faces such as flaps, ailerons, variable wing sweep and spoilers are used to trim the aircraft for other flight conditions. The appearance of the morphing wing concept launched a new challenge in the area of overall wing and aircraft performance improvement during different flight segments by locally altering the flow over the aircraft's wings. This paper describes the development and appli-cation of a control system for an actuation mechanism integrated in a new morphing wing structure. The controlled actuation system includes four similar miniature electromechanical actuators dis-posed in two parallel actuation lines. The experimental model of the morphing wing is based on a full-scale portion of an aircraft wing, which is equipped with an aileron. The upper surface of the wing is a flexible one, being closed to the wing tip; the flexible skin is made of light composite materials. The four actuators are controlled in unison to change the flexible upper surface to improve the flow quality on the upper surface by delaying or advancing the transition point from laminar to turbulent regime. The actuators transform the torque into vertical forces. Their bases are fixed on the wing ribs and their top link arms are attached to supporting plates fixed onto the flex-ible skin with screws. The actuators push or pull the flexible skin using the necessary torque until the desired vertical displacement of each actuator is achieved. The four vertical displacements of the actuators, correlated with the new shape of the wing, are provided by a database obtained through a preliminary aerodynamic optimization for specific flight conditions. The control system is designed to control the positions of the actuators in real time in order to obtain and to maintain the desired shape of the wing for a specified flight condition. The feasibility and effectiveness of the developed control system by use of a proportional fuzzy feed-forward methodology are demon-strated experimentally through bench and wind tunnel tests of the morphing wing model.     

Transient aeroelastic responses and flutter analysis of a variable-span wing during the morphing process

To investigate the transient aeroelastic responses and flutter characteristics of a variablespan wing during the morphing process,a novel frst-order state-space aeroelastic model is proposed.The time-varying structural model of the morphing wing is established based on the Euler-Bernoulli beam theory with time-dependent boundary conditions.A nondimensionalization method is used to translate the time-dependent boundary conditions to be time-independent.The time-domain aerodynamic forces are calculated by the reduced-order unsteady vortex lattice method.The morphing parameters,i.e.,wing span length and morphing speed,are of particular interest for understanding the fundamental aeroelastic behavior of variable-span wings.A test case is proposed and numerical results indicate that the flutter characteristics are sensitive to both of the two morphing parameters.It could be noticed that the aeroelastic characteristics during the wing extracting process are more serious than those during the extending process at the same morphing speed by transient aeroelastic response analysis.In addition,a faster morphing process can get better aeroelastic performance while the mechanism comlexity will arise.     

Nonlinear dynamics of a flapping rotary wing: Modeling and optimal wing kinematic analysis

The analysis of the passive rotation feature of a micro Flapping Rotary Wing(FRW)applicable for Micro Air Vehicle(MAV) design is presented in this paper. The dynamics of the wing and its influence on aerodynamic performance of FRW is studied at low Reynolds number(~10~3).The FRW is modeled as a simplified system of three rigid bodies: a rotary base with two flapping wings. The multibody dynamic theory is employed to derive the motion equations for FRW. A quasi-steady aerodynamic model is utilized for the calculation of the aerodynamic forces and moments. The dynamic motion process and the effects of the kinematics of wings on the dynamic rotational equilibrium of FWR and the aerodynamic performances are studied. The results show that the passive rotation motion of the wings is a continuous dynamic process which converges into an equilibrium rotary velocity due to the interaction between aerodynamic thrust, drag force and wing inertia. This causes a unique dynamic time-lag phenomena of lift generation for FRW, unlike the normal flapping wing flight vehicle driven by its own motor to actively rotate its wings. The analysis also shows that in order to acquire a high positive lift generation with high power efficiency and small dynamic time-lag, a relative high mid-up stroke angle within 7–15° and low mid-down stroke angle within -40° to -35° are necessary. The results provide a quantified guidance for design option of FRW together with the optimal kinematics of motion according to flight performance requirement.     

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.     

双滑轨式机翼前掠机构设计

为了满足变体飞机在气动和结构方面的要求,基于变前掠翼布局,提出一种双滑轨式的翼身连动机构,使飞机气动布局可以在平直翼、前掠翼、三角翼之间自由转换。首先,通过结构框图和三维模型图对双滑轨式翼身连动机构进行了总体概述;其次,对设计过程中的具体问题进行了说明;最后,从功能实现和结构设计两个方面对双滑轨式翼身连动机构和传统单转轴式翼身连动机构进行了对比分析。双滑轨式翼身连动机构可以较好地满足气动外形变化的要求,并且,在同等条件下使翼根处载荷减小35.6%,转轴处载荷减小7.2%。因此,本方案可以作为变体飞机设计过程中的一种参考方案。     

Experimental validation of a new morphing trailing edge system using Price – Païdoussis wind tunnel tests

This paper presents the design and manufacturing of a new morphing wing system carried out at the Laboratory of Applied Research in Active Controls, Avionics and AeroServoElasticity(LARCASE) at the ETS in Montréal. This first version of a morphing wing allows the deformation of its trailing edge, denote by Morphing Trailing Edge(MTE). In order to characterize the technical impact of this deformation, we compare its performance with that of a rigid aileron by testing in the LARCASE's price-Pa?doussis subsonic wind tunnel. The first set of results shows that it is possible to replace an aileron by a MTE on a wing, as an improvement was observed for the MTE aerodynamic performances with respect to the aileron aerodynamic performances.The improvement consisted in the fact that the drag coefficient was smaller, and the lift-to-drag ratio was higher for the same lift coefficient.