Aeroelastic control is a critical technique for high-aspect-ratio flexible wings.A novel aeroelastic control method is introduced,utilizing the internal Moving Mass Control(MMC)technique,which demonstrates the potenti...Aeroelastic control is a critical technique for high-aspect-ratio flexible wings.A novel aeroelastic control method is introduced,utilizing the internal Moving Mass Control(MMC)technique,which demonstrates the potential to fulfill hybrid control demands without incurring a drag penalty.Dynamic equations for a flexible wing equipped with a spanwise moving mass under unsteady aerodynamic loading are derived using mass position as the input variable.Controloriented analyses indicate that intrinsic structural frequencies,flutter characteristics,and gust response can be actively modified by varying the spanwise and chordwise positions of the mass element.Among these,the chordwise position exerts a more significant impact on the structural modes and flutter speed of the wing.A hybrid aeroelastic control system,incorporating motion planning and control law,is proposed to evaluate real-time performance in Active Flutter Suppression(AFS)and Gust Load Alleviation(GLA).Control outcomes suggest that,with a mass ratio of 1/16 and a half-chord installation area for the guide rail,flutter speed increases by about 10%.Additionally,excitation amplitudes across different gust frequencies are substantially mitigated,achieving a maximum reduction of vibration amplitude by about 73%.These findings offer a comprehensive understanding of the MMC technique and its application to flexible aircraft.展开更多
This paper presents a novel modelling method to study the thrust generation mechanism of biplane flapping wings made of thin and highly deformable membrane.Based on the principle of strain energy equivalence,the membr...This paper presents a novel modelling method to study the thrust generation mechanism of biplane flapping wings made of thin and highly deformable membrane.Based on the principle of strain energy equivalence,the membrane structures were modelled by mass-spring systems.The aerodynamic loads were calculated by a simplified quasi-steady aerodynamic model with consideration of the clap-and-fling mechanism.The impact force was introduced into the system when two wing surfaces were in contact.For wing-dynamics simulation problems,convergence analyses were conducted to obtain suitable mesh resolution.To validate the present modelling method,the predicted thrust and required power of a biplane flapping-wing air vehicle were compared with the experimental data.The effect of the forward speed was also analyzed in this paper.It was shown that as the forward speed increases the thrust production efficiency becomes lower together with smaller wing deformation.展开更多
Monitoring the shape and deformation of morphing wings is vital for ensuring multi-mission flight and safety operation.During the morphing process,the complex deformation of the flexible skin wing usually involves lar...Monitoring the shape and deformation of morphing wings is vital for ensuring multi-mission flight and safety operation.During the morphing process,the complex deformation of the flexible skin wing usually involves large amounts of movement,shearing,bending,and distortion.This paper proposes an improved stereo-digital image correlation measurement system designed to characterize full-field complex large deformation of flexible skin shear variable-sweep wings(SVSWs).By minimizing reference image updating frequency using the proposed conditional incremental strategy,effectively addressing the computational failures caused by image decorrelation due to complex large deformations.To improve tracking efficiency and accuracy of uncoded targets in complex backgrounds,an automatic subpixel detection method for circular diagonal targets is presented.A series of experiments are performed on a 1200 mm span flexible skin SVSW to verify the proposed methods.The results show that the length and angle measurement accuracies are better than 0.11 mm and 0.05°,respectively.Based on the measured morphing geometry parameters,displacement and strain fields,the structural integrity and morphing performance of the wing under different loads are discussed.During the shear variable-sweep process,the wingtip load dominates the deflection distribution,while its effect on the strain distribution is relatively minor.The proposed method and system can provide reliable data support for the structural optimization design and safety evaluation of such morphing wings.展开更多
Based on research into bionic butterflies for environmental detection and ecological management,a scheme was proposed to develop and manufacture a bionic aircraft with two wings inspired by specific butterfly species....Based on research into bionic butterflies for environmental detection and ecological management,a scheme was proposed to develop and manufacture a bionic aircraft with two wings inspired by specific butterfly species.A flapping-wing aircraft with a simple structure was designed,and its two-wing design was optimized.The research focused on several key areas:the design and optimization of the wings,the development of the transmission mechanism,hardware design and fabrication,and 3D printing for component manufacturing.This resulted in the bionic replication of the wing shape and structure of the Tiger Papilio butterfly.The final bionic butterfly features a wingspan of 29.5 cm and a total weight of 13.8 g.This project integrates mechatronic principles and provides a valuable reference for advancements in the field of bionic butterflies.Future research could explore the aerodynamic characteristics of wings and innovative design approaches in greater depth.展开更多
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 structu...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.展开更多
To investigate the control of morphing wings by means of interacting effectors,this article proposes a distributed coordinated control scheme with sampled communication on the basis of a simple morphing wing model,est...To investigate the control of morphing wings by means of interacting effectors,this article proposes a distributed coordinated control scheme with sampled communication on the basis of a simple morphing wing model,established with arrayed agents. The control scheme can change the shape of airfoil into an expected one and keep it smooth during morphing. As the interconnection of communication network and the agents would make the behavior of the morphing wing system complicated,a diagrammatic stability analysis method is put forward to ensure the system stability. Two simulations are carried out on the morphing wing system by using MATLAB. The results stand witness to the feasibility of the distributed coordinated control scheme and the effectiveness of the diagrammatic stability analysis method.展开更多
Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regi...Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV＇s, inclu- ding massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment （larger dimension） is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.展开更多
The achievement of laminar flow in the boundary layer at high-speed cruise conditions may further, in addition to shock-wave control, reduce the drag and extend the range of military fighter aircraft. To this end, a f...The achievement of laminar flow in the boundary layer at high-speed cruise conditions may further, in addition to shock-wave control, reduce the drag and extend the range of military fighter aircraft. To this end, a further investigation on transitional boundary-layer flow of fighter wings is needed due to different configurations from the wings used on conventional transport aircraft. In this paper, wind tunnel experiments and numerical simulations were conducted on three-dimensional transition of thin diamond-shaped wings used on advanced fighter aircraft at tran/supersonic design points. A newly proposed correlation of crossflow transition which includes the effect of surface roughness was introduced into the c-Rehttransition model. Predicted results were in good agreement with flow visualizations. Results showed that the strength of the crossflow component grew rapidly around the leading edge because of the severe flow acceleration, just as the same as wings with a large aspect ratio. However, there seemed no regular pattern of instabilitydominance variation in span-wise for a diamond configuration. The dominance of different instability mechanisms strongly depended on the local pressure distribution. Hereby, the research recommended a ‘‘roof-like" shape of pressure distribution to suppress both crossflow and Tollmien-Schlichting(T-S) instabilities. Besides, a sharp suction peak with a serious pressure rise should be cut off to avoid stronger instabilities. Further discussions also revealed an independence of the unit Reynolds number when transition was triggered by T-S instabilities. Aerodynamic force comparisons indicated that further benefit on drag reduction could be expected by including the three-dimensional transition effect into a wing design process.展开更多
Flying insects are capable of flapping their wings to provide the required power and control forces for flight.A coordinated organizational system including muscles,wings,and control architecture plays a significant r...Flying insects are capable of flapping their wings to provide the required power and control forces for flight.A coordinated organizational system including muscles,wings,and control architecture plays a significant role,which provides the sources of inspiration for designing flapping-wing vehicles.In recent years,due to the development of micro-and meso-scale manufacturing technologies,advances in components technologies have directly led to a progress of smaller Flapping-Wing Nano Air Vehicles(FWNAVs)around gram and sub-gram scales,and these air vehicles have gradually acquired insect-like locomotive strategies and capabilities.This paper will present a selective review of components technologies for ultra-lightweight flapping-wing nano air vehicles under 3 g,which covers the novel propulsion methods such as artificial muscles,flight control mechanisms,and the design paradigms of the insect-inspired wings,with a special focus on the development of the driving technologies based on artificial muscles and the progress of the biomimetic wings.The challenges involved in constructing such small flapping-wing air vehicles and recommendations for several possible future directions in terms of component technology enhancements and overall vehicle performance are also discussed in this paper.This review will provide the essential guidelines and the insights for designing a flapping-wing nano air vehicle with higher performance.展开更多
Machine learning has been widely utilized in flow field modeling and aerodynamic optimization.However,most applications are limited to two-dimensional problems.The dimensionality and the cost per simulation of three-d...Machine learning has been widely utilized in flow field modeling and aerodynamic optimization.However,most applications are limited to two-dimensional problems.The dimensionality and the cost per simulation of three-dimensional problems are so high that it is often too expensive to prepare sufficient samples.Therefore,transfer learning has become a promising approach to reuse well-trained two-dimensional models and greatly reduce the need for samples for threedimensional problems.This paper proposes to reuse the baseline models trained on supercritical airfoils to predict finite-span swept supercritical wings,where the simple swept theory is embedded to improve the prediction accuracy.Two baseline models are investigated:one is commonly referred to as the forward problem of predicting the pressure coefficient distribution based on the geometry,and the other is the inverse problem that predicts the geometry based on the pressure coefficient distribution.Two transfer learning strategies are compared for both baseline models.The transferred models are then tested on complete wings.The results show that transfer learning requires only approximately 500 wing samples to achieve good prediction accuracy on different wing planforms and different free stream conditions.Compared to the two baseline models,the transferred models reduce the prediction error by 60%and 80%,respectively.展开更多
Variable-sweep wings have large shape-changing capabilities and wide flight envelops,which are considered as one of the most promising directions for intelligent morphing UAVs.Aerodynamic investigations always focus o...Variable-sweep wings have large shape-changing capabilities and wide flight envelops,which are considered as one of the most promising directions for intelligent morphing UAVs.Aerodynamic investigations always focus on several static states in the varying sweep process,which ignore the unsteady aerodynamic characteristics.However,deviations to static aerodynamic forces are inevitably caused by dynamic sweep motion.In this work,first,unsteady aerodynamic characteristics on a typical variable-sweep UAV with large aspect ratio were analyzed.Then,deep mechanism of unsteady aerodynamic characteristics in the varying sweep process was studied.Finally,numerical simulation method integrated with structured moving overset grids was applied to solve the unsteady fluid of varying sweep process.The simulation results of a sweep forward-backward circle show a distinct dynamic hysteresis loop surrounding the static data for the aerodynamic forces.Compared with the static lift coefficients,at the same sweep angles,dynamic lift coefficient in sweep forward process are all smaller,while dynamic sweep backward lift coefficient are all larger.In addition,dynamic deviations to static lift coefficient are positively related with the varying sweep speeds.Mechanism study on the unsteady aerodynamic characteristics indicates that three key factors lead to the dynamic hysteresis loop in varying sweep process.They are the effects of additional velocity caused by varying sweep motion,the effects of flow hysteresis and viscosity.The additional velocity induced by sweep motion affects the transversal flow direction along the wing and the effective angle of attack at the airfoil profile.The physical properties of flow,the hysteresis and viscosity affect the unsteady aerodynamic characteristics by flow separation and induced vortexes.展开更多
The manufacturing cost is a significant factor that must be considered in the structural design of a composite wing. A multi-objective optimization method for the tradeoff between manufacturing cost and weight of comp...The manufacturing cost is a significant factor that must be considered in the structural design of a composite wing. A multi-objective optimization method for the tradeoff between manufacturing cost and weight of composite wing structure is de- veloped by integrating the manufacturing cost model into the traditional wing structural optimization. A two-level optimization method is proposed to carry out the tradeoff between manufacturing cost and weight, in which the design variables include both structural layout and dimensions and a cost model is incorporated into structural optimization. The manufacturing cost model for a composite wing and the detail procedure for solving this tradeoff problem are presented. The application of the method to the composite wing structural design of an unmanned aerial vehicle is illustrated to verify the method. The application indicates that the method is able to find the Pareto optimal set of minimum structural weight and manufacturing cost. Based on the Pareto optimal set, one can conduct the tradeoff between manufacturing cost and weight of wing structures.展开更多
This paper aims to reveal the multi-optimal mechanisms for dynamic control in drag- onfly wings. By combining the Arnold circulation with such micro/nano structures as the hollow inside constructions of the pterostigm...This paper aims to reveal the multi-optimal mechanisms for dynamic control in drag- onfly wings. By combining the Arnold circulation with such micro/nano structures as the hollow inside constructions of the pterostigma, veins and spikes, dragonfly wings can create variable mass, variable rotating inertia and variable natural frequency. This marvelous ability enables dragonflies to overcome the contradictory requirements of both light-weight-wing and heavy-weight-wing, and displays the multi-optimal mechanisms for the excellent flying ability and dynamic control capac- ity of dragonflies. These results provide new perspectives for understanding the wings＇ functions and new inspirations for bionic manufactures.展开更多
Nowadays, the importance of identifying the flight mechanisms of the dragonfly, as an inspiration for designing flapping wing vehicles, is well known. An experimental approach to understanding the complexities of inse...Nowadays, the importance of identifying the flight mechanisms of the dragonfly, as an inspiration for designing flapping wing vehicles, is well known. An experimental approach to understanding the complexities of insect wings as organs of flight could provide significant outcomes for design purposes. In this paper, a comprehensive investigation is carried out on the morphological and microstructural features of dragonfly wings. Scanning electron microscopy （SEM） and tensile testing are used to experimentally verify the functional roles of different parts of the wings. A number of SEM images of the elements of the wings, such as the nodus, leading edge, trailing edge, and vein sections, which play dominant roles in strengthening the whole structure, are presented. The results from the tensile tests indicate that the nodus might be the critical region of the wing that is subjected to high tensile stresses. Considering the patterns of the longitudinal corrugations of the wings obtained in this paper, it can be supposed that they increase the load-bearing capacity, giving the wings an ability to tolerate dynamic loading conditions. In addition, it is suggested that the longitudinal veins, along with the leading and trailing edges, are structural mechanisms that further improve fatigue resistance by providing higher fracture toughness, preventing crack propagation, and allowing the wings to sustain a significant amount of damage without loss of strength.展开更多
An investigation of the hysteresis of vortex breakdown over pitching-up deltawings is presented. Based on experiments, there are two main reasons which can be usedto explain the hysteresis of vortex breakdown. One is ...An investigation of the hysteresis of vortex breakdown over pitching-up deltawings is presented. Based on experiments, there are two main reasons which can be usedto explain the hysteresis of vortex breakdown. One is the time or phase lag due to the ini-tial suPerPOsition of linearized small disturbance, which enlarges the range of the incidenceof keeping attached flow and postpones the initial incidence of vortex breakdown. Theother is the reduction of adverse pressure gradient due to the periphery centrifugal instabil-ity after the concentrated vortex has come into being, which is the key reason of hystere-sis of vortex breakdown- The structure of vortex over a pitching up delta wing can be di-vided into three layers, which is not a significant a1teration compared with that of vortexover a static delta wing.展开更多
基金supported by the National Natural Science Foundation of China(No.12102096)the Guangdong Basic and Applied Basic Research Foundation,China(No.2022A1515011885)the Research Fund of National Key Laboratory of Aerospace Physics in Fluids,China(No.2024-APF-KFQMJJ-08)。
文摘Aeroelastic control is a critical technique for high-aspect-ratio flexible wings.A novel aeroelastic control method is introduced,utilizing the internal Moving Mass Control(MMC)technique,which demonstrates the potential to fulfill hybrid control demands without incurring a drag penalty.Dynamic equations for a flexible wing equipped with a spanwise moving mass under unsteady aerodynamic loading are derived using mass position as the input variable.Controloriented analyses indicate that intrinsic structural frequencies,flutter characteristics,and gust response can be actively modified by varying the spanwise and chordwise positions of the mass element.Among these,the chordwise position exerts a more significant impact on the structural modes and flutter speed of the wing.A hybrid aeroelastic control system,incorporating motion planning and control law,is proposed to evaluate real-time performance in Active Flutter Suppression(AFS)and Gust Load Alleviation(GLA).Control outcomes suggest that,with a mass ratio of 1/16 and a half-chord installation area for the guide rail,flutter speed increases by about 10%.Additionally,excitation amplitudes across different gust frequencies are substantially mitigated,achieving a maximum reduction of vibration amplitude by about 73%.These findings offer a comprehensive understanding of the MMC technique and its application to flexible aircraft.
基金funded by Vietnam National Foundation for Science and Technology Development(NAFOSTED)(Grant No.107.01-2021.39).
文摘This paper presents a novel modelling method to study the thrust generation mechanism of biplane flapping wings made of thin and highly deformable membrane.Based on the principle of strain energy equivalence,the membrane structures were modelled by mass-spring systems.The aerodynamic loads were calculated by a simplified quasi-steady aerodynamic model with consideration of the clap-and-fling mechanism.The impact force was introduced into the system when two wing surfaces were in contact.For wing-dynamics simulation problems,convergence analyses were conducted to obtain suitable mesh resolution.To validate the present modelling method,the predicted thrust and required power of a biplane flapping-wing air vehicle were compared with the experimental data.The effect of the forward speed was also analyzed in this paper.It was shown that as the forward speed increases the thrust production efficiency becomes lower together with smaller wing deformation.
基金supported by the National Natural Science Foundation of China(Grant Nos.12202282 and 12102267).
文摘Monitoring the shape and deformation of morphing wings is vital for ensuring multi-mission flight and safety operation.During the morphing process,the complex deformation of the flexible skin wing usually involves large amounts of movement,shearing,bending,and distortion.This paper proposes an improved stereo-digital image correlation measurement system designed to characterize full-field complex large deformation of flexible skin shear variable-sweep wings(SVSWs).By minimizing reference image updating frequency using the proposed conditional incremental strategy,effectively addressing the computational failures caused by image decorrelation due to complex large deformations.To improve tracking efficiency and accuracy of uncoded targets in complex backgrounds,an automatic subpixel detection method for circular diagonal targets is presented.A series of experiments are performed on a 1200 mm span flexible skin SVSW to verify the proposed methods.The results show that the length and angle measurement accuracies are better than 0.11 mm and 0.05°,respectively.Based on the measured morphing geometry parameters,displacement and strain fields,the structural integrity and morphing performance of the wing under different loads are discussed.During the shear variable-sweep process,the wingtip load dominates the deflection distribution,while its effect on the strain distribution is relatively minor.The proposed method and system can provide reliable data support for the structural optimization design and safety evaluation of such morphing wings.
基金2023 Innovation and Entrepreneurship Training Project of Hunan College Students:Tiger Butterfly—Bionic Manufacturing and Morphology Research(Project No.S202313809022)Key Project of Education Reform of Hunan Provincial Department of Education:Research on Disciplinary Integration Education Model under Intelligence+Empowerment—A Case Study of Robotics and Logistics Management Majors(Project No.HNJG-20231561)。
文摘Based on research into bionic butterflies for environmental detection and ecological management,a scheme was proposed to develop and manufacture a bionic aircraft with two wings inspired by specific butterfly species.A flapping-wing aircraft with a simple structure was designed,and its two-wing design was optimized.The research focused on several key areas:the design and optimization of the wings,the development of the transmission mechanism,hardware design and fabrication,and 3D printing for component manufacturing.This resulted in the bionic replication of the wing shape and structure of the Tiger Papilio butterfly.The final bionic butterfly features a wingspan of 29.5 cm and a total weight of 13.8 g.This project integrates mechatronic principles and provides a valuable reference for advancements in the field of bionic butterflies.Future research could explore the aerodynamic characteristics of wings and innovative design approaches in greater depth.
基金supported by the National Natural Science Foundation of China(grant number 31970454)the Aviation Science Foundation of China(2020Z0740R4001)+1 种基金the Graduate Innovation Fund of Jilin University(2022189)Undergraduate Innovation and Entrepreneurship Training Program Project of Jilin University(S202210183259).
文摘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.
基金National Natural Science Foundation of China (90605007)
文摘To investigate the control of morphing wings by means of interacting effectors,this article proposes a distributed coordinated control scheme with sampled communication on the basis of a simple morphing wing model,established with arrayed agents. The control scheme can change the shape of airfoil into an expected one and keep it smooth during morphing. As the interconnection of communication network and the agents would make the behavior of the morphing wing system complicated,a diagrammatic stability analysis method is put forward to ensure the system stability. Two simulations are carried out on the morphing wing system by using MATLAB. The results stand witness to the feasibility of the distributed coordinated control scheme and the effectiveness of the diagrammatic stability analysis method.
基金a Multidisciplinary University Research Initiative (MURI) project sponsored by AFOSR
文摘Micro air vehicles （MAV＇s） have the potential to revolutionize our sensing and information gathering capabilities in environmental monitoring and homeland security areas. Due to the MAV＇s＇ small size, flight regime, and modes of operation, significant scientific advancement will be needed to create this revolutionary capability. Aerodynamics, structural dynamics, and flight dynamics of natural flyers intersects with some of the richest problems in MAV＇s, inclu- ding massively unsteady three-dimensional separation, transition in boundary layers and shear layers, vortical flows and bluff body flows, unsteady flight environment, aeroelasticity, and nonlinear and adaptive control are just a few examples. A challenge is that the scaling of both fluid dynamics and structural dynamics between smaller natural flyer and practical flying hardware/lab experiment （larger dimension） is fundamentally difficult. In this paper, we offer an overview of the challenges and issues, along with sample results illustrating some of the efforts made from a computational modeling angle.
基金supported by the National Natural Science Foundation of China (No.11372254)
文摘The achievement of laminar flow in the boundary layer at high-speed cruise conditions may further, in addition to shock-wave control, reduce the drag and extend the range of military fighter aircraft. To this end, a further investigation on transitional boundary-layer flow of fighter wings is needed due to different configurations from the wings used on conventional transport aircraft. In this paper, wind tunnel experiments and numerical simulations were conducted on three-dimensional transition of thin diamond-shaped wings used on advanced fighter aircraft at tran/supersonic design points. A newly proposed correlation of crossflow transition which includes the effect of surface roughness was introduced into the c-Rehttransition model. Predicted results were in good agreement with flow visualizations. Results showed that the strength of the crossflow component grew rapidly around the leading edge because of the severe flow acceleration, just as the same as wings with a large aspect ratio. However, there seemed no regular pattern of instabilitydominance variation in span-wise for a diamond configuration. The dominance of different instability mechanisms strongly depended on the local pressure distribution. Hereby, the research recommended a ‘‘roof-like" shape of pressure distribution to suppress both crossflow and Tollmien-Schlichting(T-S) instabilities. Besides, a sharp suction peak with a serious pressure rise should be cut off to avoid stronger instabilities. Further discussions also revealed an independence of the unit Reynolds number when transition was triggered by T-S instabilities. Aerodynamic force comparisons indicated that further benefit on drag reduction could be expected by including the three-dimensional transition effect into a wing design process.
基金supported by the National Natural Science Foundation of China(Nos.52175277,51905431).
文摘Flying insects are capable of flapping their wings to provide the required power and control forces for flight.A coordinated organizational system including muscles,wings,and control architecture plays a significant role,which provides the sources of inspiration for designing flapping-wing vehicles.In recent years,due to the development of micro-and meso-scale manufacturing technologies,advances in components technologies have directly led to a progress of smaller Flapping-Wing Nano Air Vehicles(FWNAVs)around gram and sub-gram scales,and these air vehicles have gradually acquired insect-like locomotive strategies and capabilities.This paper will present a selective review of components technologies for ultra-lightweight flapping-wing nano air vehicles under 3 g,which covers the novel propulsion methods such as artificial muscles,flight control mechanisms,and the design paradigms of the insect-inspired wings,with a special focus on the development of the driving technologies based on artificial muscles and the progress of the biomimetic wings.The challenges involved in constructing such small flapping-wing air vehicles and recommendations for several possible future directions in terms of component technology enhancements and overall vehicle performance are also discussed in this paper.This review will provide the essential guidelines and the insights for designing a flapping-wing nano air vehicle with higher performance.
基金supported by the National Natural Science Foundation of China(Nos.92052203,12202243 and 11872230).
文摘Machine learning has been widely utilized in flow field modeling and aerodynamic optimization.However,most applications are limited to two-dimensional problems.The dimensionality and the cost per simulation of three-dimensional problems are so high that it is often too expensive to prepare sufficient samples.Therefore,transfer learning has become a promising approach to reuse well-trained two-dimensional models and greatly reduce the need for samples for threedimensional problems.This paper proposes to reuse the baseline models trained on supercritical airfoils to predict finite-span swept supercritical wings,where the simple swept theory is embedded to improve the prediction accuracy.Two baseline models are investigated:one is commonly referred to as the forward problem of predicting the pressure coefficient distribution based on the geometry,and the other is the inverse problem that predicts the geometry based on the pressure coefficient distribution.Two transfer learning strategies are compared for both baseline models.The transferred models are then tested on complete wings.The results show that transfer learning requires only approximately 500 wing samples to achieve good prediction accuracy on different wing planforms and different free stream conditions.Compared to the two baseline models,the transferred models reduce the prediction error by 60%and 80%,respectively.
基金supported by the National Natural Science Foundation of China(No.12202384)the Rotor Aerodynamics Key Laboratory Foundation of China Aerodynamics Research and Development Center(No.2108RAL202102-5).
文摘Variable-sweep wings have large shape-changing capabilities and wide flight envelops,which are considered as one of the most promising directions for intelligent morphing UAVs.Aerodynamic investigations always focus on several static states in the varying sweep process,which ignore the unsteady aerodynamic characteristics.However,deviations to static aerodynamic forces are inevitably caused by dynamic sweep motion.In this work,first,unsteady aerodynamic characteristics on a typical variable-sweep UAV with large aspect ratio were analyzed.Then,deep mechanism of unsteady aerodynamic characteristics in the varying sweep process was studied.Finally,numerical simulation method integrated with structured moving overset grids was applied to solve the unsteady fluid of varying sweep process.The simulation results of a sweep forward-backward circle show a distinct dynamic hysteresis loop surrounding the static data for the aerodynamic forces.Compared with the static lift coefficients,at the same sweep angles,dynamic lift coefficient in sweep forward process are all smaller,while dynamic sweep backward lift coefficient are all larger.In addition,dynamic deviations to static lift coefficient are positively related with the varying sweep speeds.Mechanism study on the unsteady aerodynamic characteristics indicates that three key factors lead to the dynamic hysteresis loop in varying sweep process.They are the effects of additional velocity caused by varying sweep motion,the effects of flow hysteresis and viscosity.The additional velocity induced by sweep motion affects the transversal flow direction along the wing and the effective angle of attack at the airfoil profile.The physical properties of flow,the hysteresis and viscosity affect the unsteady aerodynamic characteristics by flow separation and induced vortexes.
文摘The manufacturing cost is a significant factor that must be considered in the structural design of a composite wing. A multi-objective optimization method for the tradeoff between manufacturing cost and weight of composite wing structure is de- veloped by integrating the manufacturing cost model into the traditional wing structural optimization. A two-level optimization method is proposed to carry out the tradeoff between manufacturing cost and weight, in which the design variables include both structural layout and dimensions and a cost model is incorporated into structural optimization. The manufacturing cost model for a composite wing and the detail procedure for solving this tradeoff problem are presented. The application of the method to the composite wing structural design of an unmanned aerial vehicle is illustrated to verify the method. The application indicates that the method is able to find the Pareto optimal set of minimum structural weight and manufacturing cost. Based on the Pareto optimal set, one can conduct the tradeoff between manufacturing cost and weight of wing structures.
基金Project supported by the National Natural Science Foundation of China (Nos. 11102138 and 11272175)the Fundamental Research Funds for the Central Universities
文摘This paper aims to reveal the multi-optimal mechanisms for dynamic control in drag- onfly wings. By combining the Arnold circulation with such micro/nano structures as the hollow inside constructions of the pterostigma, veins and spikes, dragonfly wings can create variable mass, variable rotating inertia and variable natural frequency. This marvelous ability enables dragonflies to overcome the contradictory requirements of both light-weight-wing and heavy-weight-wing, and displays the multi-optimal mechanisms for the excellent flying ability and dynamic control capac- ity of dragonflies. These results provide new perspectives for understanding the wings＇ functions and new inspirations for bionic manufactures.
文摘Nowadays, the importance of identifying the flight mechanisms of the dragonfly, as an inspiration for designing flapping wing vehicles, is well known. An experimental approach to understanding the complexities of insect wings as organs of flight could provide significant outcomes for design purposes. In this paper, a comprehensive investigation is carried out on the morphological and microstructural features of dragonfly wings. Scanning electron microscopy （SEM） and tensile testing are used to experimentally verify the functional roles of different parts of the wings. A number of SEM images of the elements of the wings, such as the nodus, leading edge, trailing edge, and vein sections, which play dominant roles in strengthening the whole structure, are presented. The results from the tensile tests indicate that the nodus might be the critical region of the wing that is subjected to high tensile stresses. Considering the patterns of the longitudinal corrugations of the wings obtained in this paper, it can be supposed that they increase the load-bearing capacity, giving the wings an ability to tolerate dynamic loading conditions. In addition, it is suggested that the longitudinal veins, along with the leading and trailing edges, are structural mechanisms that further improve fatigue resistance by providing higher fracture toughness, preventing crack propagation, and allowing the wings to sustain a significant amount of damage without loss of strength.
文摘An investigation of the hysteresis of vortex breakdown over pitching-up deltawings is presented. Based on experiments, there are two main reasons which can be usedto explain the hysteresis of vortex breakdown. One is the time or phase lag due to the ini-tial suPerPOsition of linearized small disturbance, which enlarges the range of the incidenceof keeping attached flow and postpones the initial incidence of vortex breakdown. Theother is the reduction of adverse pressure gradient due to the periphery centrifugal instabil-ity after the concentrated vortex has come into being, which is the key reason of hystere-sis of vortex breakdown- The structure of vortex over a pitching up delta wing can be di-vided into three layers, which is not a significant a1teration compared with that of vortexover a static delta wing.
