Morphing Airfoil Research Articles

Aerodynamic Analysis of Camber Morphing Airfoils in Transition via Computational Fluid Dynamics.

In this paper, the authors analyze an important but overlooked area, the aerodynamics of the variable camber morphing wing in transition, where 6% camber changes from 2% to 8% using the two airfoil configurations: NACA2410 and NACA8410. Many morphing works focus on analyzing the aerodynamics of a particular airfoil geometry or already morphed case. The authors mainly address "transitional" or "in-between" aerodynamics to understand the semantics of morphing in-flight and explore the linearity in the relationship when the camber rate is gradually changed. In general, morphing technologies are considered a new paradigm for next-generation aircraft designs with highly agile flight and control and a multidisciplinary optimal design process that enables aircraft to perform substantially better than current ones. Morphing aircraft adjust wing shapes conformally, promoting an enlarged flight envelope, enhanced performance, and higher energy sustainability. Whereas the recent advancement in manufacturing and material processing, composite and Smart materials has enabled the implementation of morphing wings, designing a morphing wing aircraft is more challenging than modern aircraft in terms of reliable numerical modeling and aerodynamic analysis. Hence, it is interesting to investigate modeling the transitional aerodynamics of morphing airfoils using a numerical analysis such as computational fluid dynamics. The result shows that the SST k-ω model with transition/curvature correction computes a reasonably accurate value than an analytical solution. Additionally, the is less sensitive to transition near the leading edge in airfoils. Therefore, as the camber rate changes or gradually increases, the aerodynamic behavior correspondingly changes linearly.

Morphing Air Foil NACA 6412 Inverted Using Flexure Hinges

In this paper a NACA 6412 regulated shape will be inverted to understand the behaviour of the air flow around the shape, this with the intention of convert the lifting effect to a downforce and braking effect changing the shape of the wing, displacing the trailing edge approximately 100mm over the first stage position. Using analysis as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) to depicts the operational parameters of the two stages of the inverted NACA 6412 air foil. To reach this displacement, the main idea is using a flexure hinge designed as a M-Shape beam, this flexure hinge works as a spring to allows to the morphing wing moves around the 100mm of trailing edge displacement and the spring-beam effect creates an inverse force, when the wing moves close to the110mm and does not exceed the yield strength of the Acrylonitrile butadiene styrene (ABS) of 74Mpa. As a result of this motion parameters, we could integrate a flexure hinge to an inverted air foil regulated to reach braking and downforce forces in order to slow down vehicles or aerodynamic devices.

Modeling of superelastic auxetic structures of Ti–Zr base alloy

The superelastic properties of a novel shape memory Ti–24Zr–10Nb–2Sn alloy were evaluated in two different auxetic geometrics embedded in an airfoil by the nonlinear finite element software Abaqus. In the first part, a constitutive model was developed to determine the phenomenology and mechanical response of shape memory alloy in a superelastic state. In the second part, a numerical model of re-entrant and chiral auxetic structures was developed. The beam modeling was selected due to its efficiency in contrast to the shell and 3D solid elements. The chiral structure (simple AAS and complex AAC) is accommodated within the airfoil providing flexibility and ability to withstand loads. A larger displacement with limited strain of the airfoil was observed in both conditions. Numerical results of auxetic structural elements were consistent with experimental results. This study explores the superelastic capability of novel shape memory alloys embedded with auxetic core lattice as an alternative for soft morphing airfoil. • Finite element modeling of auxetic structures were developed to simulate superelastic capacity of Ti–24Zr alloy. • Two-dimensional model of the Eppler 420 airfoil structure was developed and evaluated for external loading conditions. • A constitutive model was developed to determine the mechanical response of shape memory alloy in a superelastic state. • The maximum stress is proportional to the number of sub-cells in auxetic structures. • A larger displacement with limited strain of the airfoil was observed in simple AAS and complex AAC chiral structures.

Optimization and Design of a Flexible Droop-Nose Leading-Edge Morphing Wing Based on a Novel Black Widow Optimization Algorithm—Part I

An aerodynamic optimization for a Droop-Nose Leading-Edge (DNLE) morphing of a well-known UAV, the UAS-S45, is proposed, using a novel Black Widow Optimization (BWO) algorithm. This approach integrates the optimization algorithm with a modified Class-Shape Transformation (CST) parameterization method to enhance aerodynamic performance by minimizing drag and maximizing aerodynamic endurance at the cruise flight condition. The CST parameterization technique is used to parameterize the reference airfoil by introducing local shape changes and provide skin flexibility to obtain various optimized morphing airfoil configurations. The optimization framework uses an in-house MATLAB algorithm, while the aerodynamic calculations use the XFoil solver with flow transition estimation criteria. These results are validated with a CFD solver utilizing the Transition (γ−Reθ) Shear Stress Transport (SST) turbulence model. Numerical studies verified the effectiveness of the optimization strategy, and the optimized airfoils have shown a significant improvement in overall aerodynamic performance by up to 12.18% drag reduction compared to the reference airfoil, and an increase in aerodynamic endurance of up to 10% for the UAS-S45 optimized airfoil configurations over its reference airfoil. These results indicate the importance of leading-edge morphing in enhancing the aerodynamic efficiency of the UAS-S45 airfoil.

Aerodynamic Characteristics of Morphing Supercritical Airfoils for Aircraft with All-Stage High Performance

Morphing airfoil is a promising technology for future aircraft to realize all-stage high performance. In the present paper, a conceptual aircraft with morphing airfoil is proposed and the aerodynamic characteristics of three types of morphing airfoils (variable-camber airfoil, variable-chord airfoil, and the combination of both morphing styles) are numerically investigated. The baseline airfoil is RAE 2822 supercritical airfoil; the Reynolds-averaged Navier–Stokes method is adopted for numerical simulation of flow around airfoils, and the accuracy of the numerical simulation method is validated by comparing with experimental data. It is found that the variable-camber and -chord airfoil can not only improve the high lift characteristics at take-off stage, but also increase the lift-to-drag ratio at transonic cruise and low-speed task stages during which the required lift is continuously decreasing due to the consumption of fuel. These findings imply that aircraft with proper morphing airfoil can achieve all-stage high aerodynamic performance.

Aerodynamic Shape Optimisation of a Camber Morphing Airfoil and Noise Estimation

In order to decrease the emitted airframe noise by a two-dimensional high-lift configuration during take-off and landing performance, a morphing airfoil has been designed through a shape design optimisation procedure starting from a baseline airfoil (NLR 7301), with the aim of emulating a high-lift configuration in terms of aerodynamic performance. A methodology has been implemented to accomplish such aerodynamic improvements by means of the compressible steady RANS equations at a certain angle of attack, with the objective of maximising its lift coefficient up to equivalent values regarding the high-lift configuration, whilst respecting the imposed structural constraints to guarantee a realistic optimised design. For such purposes, a gradient-based optimisation through the discrete adjoint method has been undertaken. Once the optimised airfoil is achieved, unsteady simulations have been carried out to obtain surface pressure distributions along a certain time-span to later serve as the input data for the aeroacoustic prediction framework, based on the Farassat 1A formulation, where the subsequent results for both configurations are post-processed to allow for a comparative analysis. Conclusively, the morphing airfoil has proven to be advantageous in terms of aeroacoustics, in which the noise has been reduced with respect to the conventional high-lift configuration for a comparable lift coefficient, despite being hampered by a significant drag coefficient increase due to stall on the morphing airfoil’s trailing edge.

Robust Optimal Design and Control of a Maneuvering Morphing Airfoil

This paper presents a new approach to optimizing the design of a morphing airfoil for an unmanned aerial vehicle (UAV) by accounting for the range of possible flight trajectories that the UAV is required to be able to fly. A morphing mechanism and control system for the airfoil are simultaneously optimized to maximize how well the UAV can follow different flight trajectories. To solve the resulting concurrent optimization problem, a new solution approach incorporating robust optimization (a method for optimization under uncertainty) is proposed, which accounts for a continuous range of possible flight trajectories. This method determines the set of “worst-case” trajectories and finds a design that is optimal under them (thus ensuring better performance under any other trajectory). Results are presented comparing the robust design found using the proposed approach against designs that have only been optimized for one specific trajectory. The results show the robust design found using the proposed approach has significantly better performance over the set of worst-case trajectories than designs optimized for a single flight trajectory, guaranteeing a bound on its performance under any randomly sampled trajectory.

Comparative Aerodynamic Performance Analysis of Camber Morphing and Conventional Airfoils

This paper aims to numerically validate the aerodynamic performance and benefits of variable camber rate morphing wings, by comparing them to conventional ones with plain flaps, when deflection angles vary, assessing their D reduction or L/D improvement. Many morphing-related research works mainly focus on the design of morphing mechanisms using smart materials, and innovative mechanism designs through materials and structure advancements. However, the foundational work that establishes the motivation of morphing technology development has been overlooked in most research works. All things considered, this paper starts with the verification of the numerical model used for the aerodynamic performance analysis and then conducts the aerodynamic performance analysis of (1) variable camber rate in morphing wings and (2) variable deflection angles in conventional wings. Finally, we find matching pairs for a direct comparison to validate the effectiveness of morphing wings. As a result, we validate that variable camber morphing wings, equivalent to conventional wings with varying flap deflection angles, are improved by at least 1.7% in their L/D ratio, and up to 18.7% in their angle of attack, with α = 8° at a 3% camber morphing rate. Overall, in the entire range of α, which conceptualizes aircrafts mission planning for operation, camber morphing wings are superior in D, L/D, and their improvement rate over conventional ones. By providing the improvement rates in L/D, this paper numerically evaluates and validates the efficiency of camber morphing aircraft, the most important aspect of aircraft operation, as well as the agility and manoeuvrability, compared to conventional wing aircraft.

بهبود ضرایب آیرودینامیکی ایرفویل با تغییرشکل آزاد به کمک شبکههای عصبی و الگوریتم ژنتیک

With the advent of morphing airfoils, the aerodynamics of wind turbines and wings underwent many changes. In this study, the aerodynamic coefficients of morphing airfoil based on NACA 0015 are optimized in the range of Reynolds number 105 to 106 and the angle of attack 0 to 12 degrees using Artificial Neural Network (ANN) and Genetic Algorithm(GA). First, the airfoils were created in MATLAB software by random control points and mesh generated in Gambit software, then in two-dimensional Ansys software were simulated. The simulation results, including lift and drag coefficients, separation point and pressure center, with control points were used to train the Artificial Neural Network (ANN). The trained function is given as an input function to the Genetic Algorithm(GA) to optimize the desired coefficients.Lift coefficient, the center of pressure, separation point and lift to drag ratio were optimized as a single objective, In single-objective optimization, the lift coefficient was increased by 18% using the morphing airfoil. Also, the lift coefficient and the center of pressure, the lift coefficient and the drag coefficient were optimized as the dual-objectives optimization. In the optimization of the dual objectives, lift and drag coefficients were controlled by 0.8 and 0.03, respectively, by the morphing airfoils.

Improving the power coefficient of the Darrieus vertical axis wind turbine with the aid of morphing airfoils

With the advent of smart materials in recent years, the aviation industry and airfoils have undergone many changes. Research into the use of smart materials in aircraft wings to increase their performance and then the use of smart materials in wind turbine airfoils has begun. In this study, computational fluid dynamics and URANS equations for a three-bladed Darrieus wind turbine equipped with a morphing airfoil was used to determine the optimum blade cross-section. 250 airfoils were generated by random control points, in Gambit software, they were unstructured and generated as a sliding mesh then they were simulated in 2D Ansys using the k-ω SST turbulence model and PISO algorithm. Control points and power coefficient were used for Artificial Neural Network (ANN)training and the Genetic Algorithm(GA) was used to optimize the power coefficient. In this study, the base airfoil is NACA0015. The results of that have been very effective. For the first case (Determine the optimal cross-section of the turbine at a full round) the power coefficient of Darrieus wind turbine with the optimal cross-section increased by 42%, and the blade section(airfoil) was also drawn. For the second case(Determine the optimal cross-section in each of the four zones of the rotor), the most efficient sections(airfoils) in four-zone were obtained, increasing the turbine power coefficient by 60% was the result of this optimization.

Design of a planar hyper-redundant lockable mechanism for shape morphing using a centralized actuation method

This work presents a type of kinematically hyper-redundant manipulators, namely serial-parallel manipulators (S-PMs), for shape morphing control. The proposed S-PMs use a centralized actuation method to significantly reduce the number of actuators. The basic design concept is to use flexible limbs to actuate a serial manipulator made of passively lockable rigid parallel manipulator (PM) modules of 3-DOFs. To implement shape morphing control, a shape parametric method is proposed to establish a relationship between a morphing shape and the DOFs of the S-PMs, based on which the kinematics of this hybrid manipulator is derived. The proposed method is applied to design and control a morphing airfoil wing with specific structure and motion requirements. The achieved results demonstrate the effectiveness of the proposed method.

Aeroacoustic and aerodynamic characteristics of a morphing airfoil

PurposeThis paper aims to assess the aeroacoustic and aerodynamic performance of a morphing airfoil with a flexible trailing edge (FTE). The objective is to make a comparison of the aerodynamic noise characteristics between the conventional airfoil with a flap and morphing airfoil and analyse the noise reduction mechanisms of the morphing airfoil.Design/methodology/approachThe computational fluid dynamic method was used to calculate the aerodynamic coefficients of morphing airfoil and the Ffowcs-Williams and Hawking’s acoustic analogy methods were performed to predict the far-field noise of different airfoils.FindingsResults show that compared with the conventional airfoil, the morphing airfoil can generate higher lift and lower noise, but a greater drag. Additionally, the noise caused by the one-unit lift of the morphing airfoil is significantly lower than that of the conventional airfoil. For the morphing airfoil, the shedding vortex in the trailing edge was the main noise resource. As the angle of attack (AoA) increases, the overall sound pressure level of the morphing airfoil increases significantly. With the increase of the trailing edge deflection angle, the amplitude and the period of sound pressure of the morning airfoil fluctuation increase.Practical implicationsPresented results could be very useful during designing the morphing airfoil with FTE, which has significant advantages in aerodynamic efficiency and aeroacoustic performance.Originality/valueThis paper presents the aerodynamic and aeroacoustic characteristics of the morphing airfoil. The effect of trailing edge deflection angle and AoA on morphing airfoil was investigated. In the future, using a morphing airfoil instead of a traditional flap can reduce the aircraft`s fuel consumption and noise pollution.

Multi-scale analysis of the flexural behaviour of 3D printed cellular polymer materials: Comparison between morphing and sandwich beams

Cellular materials with tailorable properties are increasingly being used as a controllable morphing mechanism in airfoils. Nonetheless, the flexural properties of this mechanism change depending on the configuration. Thus, the aim of this paper is to identify and analyse parameters tailoring these properties. A multi-scale analysis that models reliably the behaviour of 3D printed structures is developed. Three scales are considered. The microscopic scale, where the properties of the 3D-printed material are measured. The mesoscopic scale, where mechanical properties of four different patterns, selected for their current use in morphing applications, are estimated via numerical homogenisation. The macroscopic scale, where the global bending behaviour of cellular beams is studied. Then, the mechanical behaviour of cantilever cellular beams is studied while varying their skin rigidity. Results indicate that the skin rigidity is a critical parameter tailoring the core’s behaviour. Rigid skins force the morphing airfoil to behave like a sandwich structure, while compliant skins induce a more complex behaviour.

Effect of airfoil shape on power performance of vertical axis wind turbines in dynamic stall: Symmetric Airfoils

The current design of vertical axis wind turbines (VAWTs) suffers from inevitable change in tip speed ratio, λ, in variant wind conditions due to fixed rotor speed. At relatively high wind speeds, which are promising due to high wind power potential, VAWTs operate at low λ with poor power coefficient. Morphing airfoils can be a potential solution by modifying the airfoil shape to optimal at each λ. The optimal airfoil shape for VAWTs at low λ, where dynamic stall is present, has not yet been studied in the literature, therefore, the present study addresses this gap by focusing on this regime to serve as a step towards designing morphing airfoils for VAWTs by identifying the optimal airfoil shape at low λ. The present study performs a combined analysis of three shape defining parameters, namely the airfoil maximum thickness and its position as well as the leading-edge radius, to reveal the overall design space. The analysis is based on 252 high-fidelity transient CFD simulations of 126 identical airfoil shapes. The simulations are verified and validated with three experiments. The results show that the three shape defining parameters have a fully coupled impact on the turbine power and thrust coefficients. When λ reduces from 3.0 to 2.5, the optimal airfoil changes from NACA0018–4.5/2.75 to NACA0024–4.5/3.5, that is increasing the maximum thickness from 18%c to 24%c and shifting its position from 27.5%c to 35%c, while the leading-edge radius index, I, remains 4.5. In general, reducing I from the default value of 6.0 to 4.5 is found to increase the turbine CP.

Transonic flutter characteristics of an airfoil with morphing devices

An investigation into transonic flutter characteristic of an airfoil conceived with the morphing leading and trailing edges has been carried out. Computational fluid dynamics (CFD) is used to calculate the unsteady aerodynamic force in transonic flow. An aerodynamic reduced order model (ROM) based on autoregressive model with exogenous input (ARX) is used in the numerical simulation. The flutter solution is determined by eigenvalue analysis at specific Mach number. The approach is validated by comparing the transonic flutter characteristics of the Isogai wing with relevant literatures before applied to a morphing airfoil. The study reveals that by employing the morphing trailing edge, the shock wave forms and shifts to the trailing edge at a lower Mach number, and aerodynamic force stabilization happens earlier. Meanwhile, the minimum flutter speed increases and transonic dip occurs at a lower Mach number. It is also noted that leading edge morphing has negligible effect on the appearance of the shock wave and transonic flutter. The mechanism of improving the transonic flutter characteristics by morphing technology is discussed by correlating shock wave location on airfoil surface, unsteady aerodynamics with flutter solution.

Aerodynamic Performance Estimation of Camber Morphing Airfoils for Small Unmanned Aerial Vehicle

This paper proposes a methodology to harvest the benefits of camber morphing airfoils for small unmanned aerial vehicle (SUAV) applications. Camber morphing using discrete elements was used to morph the base airfoil, which was split into two, three, and four elements, respectively, to achieve new configurations, into the target one. . In total, thirty morphed airfoil configurations were generated and tested for aerodynamic efficiency at the Reynolds numbers of 2.5 × 105 and 4.8 × 105, corresponding to loiter and cruise Reynolds numbers of a typical SUAV. The target airfoil performance could be closely achieved by combinations of 5 to 8 morphed configurations, the best of which were selected from a pool of thirty morphed airfoil configurations for the typical design specifications of SUAV. Interestingly, some morphed airfoil configurations show a reduction in drag coefficient of 1.21 to 15.17% compared to the target airfoil over a range of flight altitudes for cruise and loiter phases. Inspired by the drag reductions observed, a case study is presented for resizing a SUAV accounting for the mass addition due to the morphing system retaining the benefits of drag reduction.

Design and control of tensegrity morphing airfoils

We present a general approach of design, dynamics, and control for tensegrity morphing airfoils. Firstly, based on reduced order Class-k tensegrity dynamics, a shape control law for tensegrity systems is derived. Then, we develop a method for discretizing continuous airfoil curves based on shape accuracy. This method is compared with conventional methods (i.e. evenly spacing and cosine spacing methods). A tensegrity topology for shape controllable airfoil is proposed. A morphing tensegrity airfoil example is given to demonstrate successful shape control. This work paves a road towards integrating structure and control design, the principles developed here can also be used for 3D morphing airfoil design and control of various kinds of tensegrity structures.

Stress-based topology optimization of compliant mechanisms using nonlinear mechanics

The present work demonstrates how a light structure can be easily designed through Topology Optimization even including complex analysis and sizing criteria such as hyperelastic Neo-Hookean materials for nonlinear analysis and aggregated stress constraints. The SIMP approach was adopted and two different strategies were analysed using an in house versatile MATLAB code. MMA was used as reference optimizer (in structural optimization) whereas a unified aggregation and relaxation method was adopted to deal with stress constraints. Feasibility was analyzed from the viewpoint of allowable stress verification. Two test cases are then studied: a morphing airfoil (for aeronautical applications) and a geometric inverter (for mechanics and bio-medical applications). For both, a hyperelastic Neo-Hookean material was chosen. Finally a complementary study on the effects of constraints and the input force intensity is also presented.

Design, analysis and testing of a smart morphing airfoil actuated by SMA wires

Nowadays, weight reduction and efficiency improvement in different parts of airplanes are the most challenging issues of engineering which are being overcome by new approaches like the employment of modern sciences namely smart materials. The research on enhancement of lift coefficient of the aircraft’s wing has made it necessary to revise the use of discontinuous flaps. Design, analysis, and the test of a smart morphing airfoil are being studied in this research which is independent of traditional colossal and bulky actuators such as hydraulic jacks and various linkages by using Shape Memory Alloy wires in order to change the camber of airfoil by continuously movement of trailing edge. To this end, flexibility enhancement is evaluated by exploiting an innovative design of a novel composite beam. Flexibility creation in a composite airfoil prototype with an implemented similar design on the beam at the previous step and using shape memory alloy wires on this structure as actuator facilitates the achievement of an applicable smart morphing airfoil. In the end, by modeling and testing investigated structures, this research attempts to answer the question ‘Is it possible to anticipate real displacements of the airfoil by simulating smart airfoil structure by finite element analysis?’. The answer is affirmative with 1.31 mm root mean square error between the tail displacement of the simulated model of the airfoil and experimental results.

Structurally Consistent Class/Shape Transformation Equations for Morphing Airfoils

Camber morphing of the wing outer mold line may improve aerodynamic performance and reduce noise emissions for some aircraft. However, not all outer mold lines are obtainable from a given reference configuration as the extent to which the outer mold line can deform is restricted by both the reference airfoil shape and wing internal structure. In this Paper, the class/shape transformation parameterization method is modified for the first time to consider the kinematics of a morphing airfoil with rigid internal structure, providing structurally consistent class/shape transformation equations. Considering as an example the use of skin-based actuators and certain assumptions regarding the internal structure, accurate kinematically feasible deformed configurations are rapidly calculated without the need for structural analysis or consideration of actuation technology, enabling rapid iterative preliminary design optimization. The kinematic relations are accurate for moderate deformations (strains less than or equal to 4%) while still providing good estimates for larger deformations when comparing to finite-element analysis results.