Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves,which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces.We investiga...Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves,which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces.We investigated the micro-scale and nano-scale structures on the wing surfaces of insects and found that the hierarchical multiple roughness structures help in enhancing the hydrophobicity.After examining 10 orders and 24 species of flying Pterygotan insects,we found that micro-scale and nano-scale structures typically exist on both the upper and lower wing surfaces of flying insects.The tiny structures such as denticle or setae on the insect wings enhance the hydrophobicity,thereby enabling the wings to be cleaned more easily.And the hydrophobic insect wings undergo a transition from Cassie to Wenzel states at pitch/size ratio of about 20.In order to examine the wetting characteristics on a rough surface,a biomimetic surface with micro-scale pillars is fabricated on a silicon wafer, which exhibits the same behavior as the insect wing,with the Cassie-Wenzel transition occurring consistently around a pitch/width value of 20.展开更多
Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves and insect wings,which enhance the hydrophobicity of the natural surfaces and play a role of self-cleaning.We presented the ...Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves and insect wings,which enhance the hydrophobicity of the natural surfaces and play a role of self-cleaning.We presented the fabrication technology of a superhydrophobic surface using high energy ion beam.Artificial insect wings that mimic the morphology and the superhydrophobocity of cicada's wings were successfully fabricated using argon and oxygen ion beam treatment on a polytetrafluoroethylene (PTFE)film.The wing structures were supported by carbon/epoxy fibers as artificial flexible veins that were bonded through an autoclave process.The morphology of the fabricated surface bears a strong resemblance to the wing surface of a cicada,with contact angles greater than 160°,which could be sustained for more than two months.展开更多
Flexible insect wings deform passively under the periodic loading during flapping flight. The wing flexibility is considered as one of the specific mechanisms on improving insect flight performance. The constitutive r...Flexible insect wings deform passively under the periodic loading during flapping flight. The wing flexibility is considered as one of the specific mechanisms on improving insect flight performance. The constitutive relation of the insect wing material plays a key role on the wing deformation, but has not been clearly understood yet. A viscoelastic constitutive relation model was established based on the stress relaxation ex- periment of a dragonfly wing （in vitro）. This model was examined by the finite element analysis of the dynamic deformation response for a model insect wing under the action of the periodical inertial force in flapping. It is revealed that the viscoelastic constitutive relation is rational to characterize the biomaterial property of insect wings in contrast to the elastic one. The amplitude and form of the passive viscoelastic deformation of the wing is evidently dependent on the viscous parameters in the constitutive relation.展开更多
The effects of corrugation and wing planform （shape and aspect ratio） on the aerodynamic force production of model insect wings in sweeping （rotating after an initial start） motion at Reynolds number 200 and 3500 ...The effects of corrugation and wing planform （shape and aspect ratio） on the aerodynamic force production of model insect wings in sweeping （rotating after an initial start） motion at Reynolds number 200 and 3500 at angle of attack 40℃ are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio （AR） of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing （forewing）, hawkmoth and dragon- fly （forewing）, respectively （AR of these wings varies greatly, from 2.84 to 5.45）. The following facts are shown. （1） The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex （LEV）. （2） The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r2 （the radius of the second ：moment of wing area） is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. （3） The effects of AR are remarkably small： whenAR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients.展开更多
Flexible wings of insects and bio-inspired micro air vehicles generally deform remarkably during flapping flight owing to aerodynamic and inertial forces,which is of highly nonlinear fluid-structure interaction（FSI）...Flexible wings of insects and bio-inspired micro air vehicles generally deform remarkably during flapping flight owing to aerodynamic and inertial forces,which is of highly nonlinear fluid-structure interaction（FSI）problems.To elucidate the novel mechanisms associated with flexible wing aerodynamics in the low Reynolds number regime,we have built up a FSI model of a hawkmoth wing undergoing revolving and made an investigation on the effects of flexible wing deformation on aerodynamic performance of the revolving wing model.To take into account the characteristics of flapping wing kinematics we designed a kinematic model for the revolving wing in two-fold：acceleration and steady rotation,which are based on hovering wing kinematics of hawkmoth,Manduca sexta.Our results show that both aerodynamic and inertial forces demonstrate a pronounced increase during acceleration phase,which results in a significant wing deformation.While the aerodynamic force turns to reduce after the wing acceleration terminates due to the burst and detachment of leading-edge vortices（LEVs）,the dynamic wing deformation seem to delay the burst of LEVs and hence to augment the aerodynamic force during and even after the acceleration.During the phase of steady rotation,the flexible wing model generates more ver-tical force at higher angles of attack（40°–60°）but less horizontal force than those of a rigid wing model.This is because the wing twist in spanwise owing to aerodynamic forces results in a reduction in the effective angle of attack at wing tip,which leads to enhancing the aerodynamics performance by increasing the vertical force while reducing the horizontal force.Moreover,our results point out the importance of the fluid-structure interaction in evaluating flexible wing aerodynamics：the wing deformation does play a significant role in enhancing the aerodynamic performances but works differently during acceleration and steady rotation,which is mainly induced by inertial force in acceleration but by aerodynamic forces in steady rotation.展开更多
Mimicking insect flights were used to design and develop new engineering materials. Although extensive research was done to study various aspects of flying insects. Because the detailed mechanics and underlying princi...Mimicking insect flights were used to design and develop new engineering materials. Although extensive research was done to study various aspects of flying insects. Because the detailed mechanics and underlying principles involved in insect flights remain largely unknown. A systematic study was carried on insect flights by using a combination of several advanced techniques to develop new models for the simulation and analysis of the wing membrane and veins of three types of insect wings, namely dragonfly （Pantala flavescens Fabricius）, honeybee （Apis cerana cerana Fabricius） and fly （Sarcophaga carnaria Linnaeus）. In order to gain insights into the flight mechanics of insects, reverse engineering methods were used to establish three-dimensional geometrical models of the membranous wings, so we can make a comparative analysis. Then nano-mechanical test of the three insect wing membranes was performed to provide experimental parameter values for mechanical models in terms of nano-hardness and elastic modulus. Finally, a computational model was established by using the finite element analysis （ANSYS） to analyze and compare the wings under a variety of simplified load regimes that are concentrated force, uniform line-load and a torque. This work opened up the possibility towards developing an engineering basis for the biomimetic design of thin solid films and 2D advanced engineering composite materials.展开更多
The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grid...The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grids, under typical hovering and forward flight conditions. Both the interaction between the contralateral wings and the interaction between the body and wings are very weak, e.g. at hovering, changes in aerodynamic forces of a wing due to the present of the other wing are less than 3% and changes in aerodynamic forces of the wings due to presence of the body are less than 2%. The reason for this is as following. During each down- or up-stroke, a wing produces a vortex ring, which induces a relatively large jet-like flow inside the ring but very small flow outside the ring. The vortex rings of the left and right wings are on the two sides of the body. Thus one wing is outside vortex ring of the other wing and the body is outside the vortex rings of the left and right wings, resulting in the weak interactions.展开更多
The application of biomimetics in the development of unmanned-aerial-vehicles （UAV） has advanced to an exceptionally small scale of nano-aerial-vehicles （NAV）, which has surpassed its immediate predecessor of micr...The application of biomimetics in the development of unmanned-aerial-vehicles （UAV） has advanced to an exceptionally small scale of nano-aerial-vehicles （NAV）, which has surpassed its immediate predecessor of micro-aerial-vehicles （MAV）, leaving a vast range of development possi- bilities that MAVs have to offer. Because of the prompt advancement into the NAV research devel- opment, the true potential and challenges presented by MAV development were never solved, understood, and truly uncovered, especially under the influence of transition and low Reynolds number flow characteristics. This paper reviews a part of previous MAV research developments which are deemed important of notification; kinematics, membranes, and flapping mechanisms ranges from small birds to big insects, which resides within the transition and low Reynolds number regimes. This paper also reviews the possibility of applying a piezoelectric transmission used to pro- duce NAV flapping wing motion and mounted on a MAV, replacing the conventional motorized flapping wing transmission. Findings suggest that limited work has been done for MAVs matching these criteria. The preferred research approach has seen bias towards numerical analysis as compared to experimental analysis.展开更多
A theoretical modeling approach as well as an unsteady analytical method is used to study aerodynamic characteristics of wing flapping with asymmetric stroke-cycles in connection with an oblique stroke plane during in...A theoretical modeling approach as well as an unsteady analytical method is used to study aerodynamic characteristics of wing flapping with asymmetric stroke-cycles in connection with an oblique stroke plane during insect forward flight. It is revealed that the aerodynamic asymmetry between the downstroke and the upstroke due to stroke-asymmetrical flapping is a key to understand the flow physics of generation and modulation of the lift and the thrust. Predicted results for examples of given kinematics validate more specifically some viewpoints that the wing lift is more easily produced when the forward speed is higher and the thrust is harder, and the lift and the thrust are generated mainly during downstroke and upstroke, respectively. The effects of three controlling parameters, i.e. the angles of tilted stroke plane, the different downstroke duration ratios, and the different angles of attack in both down- and up-stroke, are further discussed. It is found that larger oblique angles of stroke planes generate larger thrust but smaller lift; larger downstroke duration ratios lead to larger thrust, while making little change in lift and input aerodynamic power; and again, a small increase of the angle of attack in downstroke or upstroke may cause remarkable changes in aerodynamic performance in the relevant stroke.展开更多
We have examined the aerodynamic effects of corrugation in model wings that closely mimic the wing movements of a forward flight bumblebee using the method of computational fluid dynamics. Various corrugated wing mode...We have examined the aerodynamic effects of corrugation in model wings that closely mimic the wing movements of a forward flight bumblebee using the method of computational fluid dynamics. Various corrugated wing models were tested （care was taken to ensure that the corrugation introduced zero camber）. Advance ratio ranging from 0 to 0.57 was considered. The results shown that at all flight speeds considered, the time courses of aerodynamic force of the corrugated wing are very close to those of the flat-plate wing. The cornlgation decreases aerodynamic force slightly. The changes in the mean location of center of pressure in the spanwise and chordwise directions resulting from the corrugation are no more than 3% of the wing chord length. The possible reason for the small aerodynamic effects of wing corrugation is that the wing operates at a large angle of attack and the flow is separated： the large angle of incidence dominates the corrugation in determining the flow around the wing, and for separated flow, the flow is much less sensitive to wing shape variation.展开更多
In this paper, we study the aerodynamic interactions between the contralateral wings and between the body and wings of a model insect, when the insect is hovering and has various translational and rotational motions, ...In this paper, we study the aerodynamic interactions between the contralateral wings and between the body and wings of a model insect, when the insect is hovering and has various translational and rotational motions, using the method numerically solving the Navier-Stokes equations over moving overset grids. The aerodynamic interactional effects are identified by compar-ing the results of a complete model insect, the corresponding wing pair, single wing and body without the wings. Horizontal, vertical and lateral translations and roll, pitch and yaw rotations at small speeds are considered. The results indicate that for the motions considered, both the interaction between the contralateral wings and the interaction between the body and wings are weak. The changes in the forces and moments of a wing due to the contralateral wing interaction, of the wings due to the pres-ence of the body, and of the body due to the presence of the wings are generally less than 4.5%. Results show that aerodynamic forces of wings and body can be measured or computed separately in the analysis of flight stability and control of hovering in-sects.展开更多
In the present work, a thorough investigation on the microstructural and morphological aspects of dragonfly wings was carried out using scanning electron microscope. Then, based on this study and the previous reports,...In the present work, a thorough investigation on the microstructural and morphological aspects of dragonfly wings was carried out using scanning electron microscope. Then, based on this study and the previous reports, a precise three-dimensional numerical model was developed and natural frequencies and vibration modes of dragonfly forewing were determined by finite element method. The results shown that dragonfly wings are made of a series of adaptive materials, which form a very complex composite structure. This bio-composite fabrication has some unique features and potential benefits. Furthermore, the numerical results show that the first natural frequency of dragonfly wings is about 168 Hz and bending is the predominant deformation mode in this stage. The accuracy of the present analysis is verified by comparison of calculated results with experimental data. This paper may be helpful for micro aerial vehicle design concerning dynamic response.展开更多
The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweepin...The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweeping)at a large angle of attack and constant angular velocity.The Reynolds number(Re)considered in the present note is 480(Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root).During the constant-speed sweeping motion,the stall is absent and large and approximately constant lift and drag coefficients can be maintained.The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows.Soon after the initial start,a vortex ring,which consists of the leading-edge vortex(LEV),the starting vortex,and the two wing-tip vortices,is formed in the wake of the wing.During the subsequent motion of the wing,a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength.This prevents the LEV from shedding.As a result, the size of the vortex ring increases approximately linearly with time,resulting in an approximately constant time rate of the first moment of vorticity,or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wing- span.The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force.展开更多
基金supported by the National Research Laboratory Program, Korea Science and Engineering Foundation Grant (Grant No. R0A-2007-000-20012-0)the Korea Research Foundation Grant (Grant No. KRF-2006-005-J03301)+1 种基金J. Hong was partially supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant No. KRP-2006-214-D00056)J. R. Lukes acknowledges partial support from the National Science Foundation (Grant No.CBET-0424101)
文摘Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves,which have an effect on the coloration of Morpho butterflies and enhance the hydrophobicity of natural surfaces.We investigated the micro-scale and nano-scale structures on the wing surfaces of insects and found that the hierarchical multiple roughness structures help in enhancing the hydrophobicity.After examining 10 orders and 24 species of flying Pterygotan insects,we found that micro-scale and nano-scale structures typically exist on both the upper and lower wing surfaces of flying insects.The tiny structures such as denticle or setae on the insect wings enhance the hydrophobicity,thereby enabling the wings to be cleaned more easily.And the hydrophobic insect wings undergo a transition from Cassie to Wenzel states at pitch/size ratio of about 20.In order to examine the wetting characteristics on a rough surface,a biomimetic surface with micro-scale pillars is fabricated on a silicon wafer, which exhibits the same behavior as the insect wing,with the Cassie-Wenzel transition occurring consistently around a pitch/width value of 20.
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education,Science and Technology(2009-0083068 and 2009-0082607)
文摘Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves and insect wings,which enhance the hydrophobicity of the natural surfaces and play a role of self-cleaning.We presented the fabrication technology of a superhydrophobic surface using high energy ion beam.Artificial insect wings that mimic the morphology and the superhydrophobocity of cicada's wings were successfully fabricated using argon and oxygen ion beam treatment on a polytetrafluoroethylene (PTFE)film.The wing structures were supported by carbon/epoxy fibers as artificial flexible veins that were bonded through an autoclave process.The morphology of the fabricated surface bears a strong resemblance to the wing surface of a cicada,with contact angles greater than 160°,which could be sustained for more than two months.
基金Project supported by the National Natural Science Foundation of China (Nos. 90305009, 10232010 and 10072066)the Innovation Project of Chinese Academy of Sciences (Nos. KJCX-SW-L04 and KJCX2-SW-L2)
文摘Flexible insect wings deform passively under the periodic loading during flapping flight. The wing flexibility is considered as one of the specific mechanisms on improving insect flight performance. The constitutive relation of the insect wing material plays a key role on the wing deformation, but has not been clearly understood yet. A viscoelastic constitutive relation model was established based on the stress relaxation ex- periment of a dragonfly wing （in vitro）. This model was examined by the finite element analysis of the dynamic deformation response for a model insect wing under the action of the periodical inertial force in flapping. It is revealed that the viscoelastic constitutive relation is rational to characterize the biomaterial property of insect wings in contrast to the elastic one. The amplitude and form of the passive viscoelastic deformation of the wing is evidently dependent on the viscous parameters in the constitutive relation.
基金The project supported by the National Natural Science Foundation of China(10232010 and 10472008)Ph.D.Student Foundation of Chinese Ministry of Education(20030006022)
文摘The effects of corrugation and wing planform （shape and aspect ratio） on the aerodynamic force production of model insect wings in sweeping （rotating after an initial start） motion at Reynolds number 200 and 3500 at angle of attack 40℃ are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio （AR） of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing （forewing）, hawkmoth and dragon- fly （forewing）, respectively （AR of these wings varies greatly, from 2.84 to 5.45）. The following facts are shown. （1） The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex （LEV）. （2） The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r2 （the radius of the second ：moment of wing area） is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. （3） The effects of AR are remarkably small： whenAR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients.
基金supported by the Grant-in-Aid for Scientific Research(21360078 and 18100002)Grant-in-Aid for Scientific Research on Innovative Areas(24120007,JSPS)
文摘Flexible wings of insects and bio-inspired micro air vehicles generally deform remarkably during flapping flight owing to aerodynamic and inertial forces,which is of highly nonlinear fluid-structure interaction（FSI）problems.To elucidate the novel mechanisms associated with flexible wing aerodynamics in the low Reynolds number regime,we have built up a FSI model of a hawkmoth wing undergoing revolving and made an investigation on the effects of flexible wing deformation on aerodynamic performance of the revolving wing model.To take into account the characteristics of flapping wing kinematics we designed a kinematic model for the revolving wing in two-fold：acceleration and steady rotation,which are based on hovering wing kinematics of hawkmoth,Manduca sexta.Our results show that both aerodynamic and inertial forces demonstrate a pronounced increase during acceleration phase,which results in a significant wing deformation.While the aerodynamic force turns to reduce after the wing acceleration terminates due to the burst and detachment of leading-edge vortices（LEVs）,the dynamic wing deformation seem to delay the burst of LEVs and hence to augment the aerodynamic force during and even after the acceleration.During the phase of steady rotation,the flexible wing model generates more ver-tical force at higher angles of attack（40°–60°）but less horizontal force than those of a rigid wing model.This is because the wing twist in spanwise owing to aerodynamic forces results in a reduction in the effective angle of attack at wing tip,which leads to enhancing the aerodynamics performance by increasing the vertical force while reducing the horizontal force.Moreover,our results point out the importance of the fluid-structure interaction in evaluating flexible wing aerodynamics：the wing deformation does play a significant role in enhancing the aerodynamic performances but works differently during acceleration and steady rotation,which is mainly induced by inertial force in acceleration but by aerodynamic forces in steady rotation.
基金Funded by the National Natural Science Foundation of China(Nos.31172144,51475204)the National Science&Technology Pillar Program of China in the Twelfth Five-Year Plan Period(2014BAD06B03)+1 种基金the Exchange Projects of the Royal Academy of Engineering,UK(Major Award,2010-2011)the "Project 985" of Jilin University
文摘Mimicking insect flights were used to design and develop new engineering materials. Although extensive research was done to study various aspects of flying insects. Because the detailed mechanics and underlying principles involved in insect flights remain largely unknown. A systematic study was carried on insect flights by using a combination of several advanced techniques to develop new models for the simulation and analysis of the wing membrane and veins of three types of insect wings, namely dragonfly （Pantala flavescens Fabricius）, honeybee （Apis cerana cerana Fabricius） and fly （Sarcophaga carnaria Linnaeus）. In order to gain insights into the flight mechanics of insects, reverse engineering methods were used to establish three-dimensional geometrical models of the membranous wings, so we can make a comparative analysis. Then nano-mechanical test of the three insect wing membranes was performed to provide experimental parameter values for mechanical models in terms of nano-hardness and elastic modulus. Finally, a computational model was established by using the finite element analysis （ANSYS） to analyze and compare the wings under a variety of simplified load regimes that are concentrated force, uniform line-load and a torque. This work opened up the possibility towards developing an engineering basis for the biomimetic design of thin solid films and 2D advanced engineering composite materials.
基金supported by the National Natural Science Foundation of China(10732030)the 111 Project (B 07009)
文摘The aerodynamic interaction between the contralateral wings and between the body and wings of a model insect are studied, by using the method of numerically solving the Navier-Stokes equations over moving overset grids, under typical hovering and forward flight conditions. Both the interaction between the contralateral wings and the interaction between the body and wings are very weak, e.g. at hovering, changes in aerodynamic forces of a wing due to the present of the other wing are less than 3% and changes in aerodynamic forces of the wings due to presence of the body are less than 2%. The reason for this is as following. During each down- or up-stroke, a wing produces a vortex ring, which induces a relatively large jet-like flow inside the ring but very small flow outside the ring. The vortex rings of the left and right wings are on the two sides of the body. Thus one wing is outside vortex ring of the other wing and the body is outside the vortex rings of the left and right wings, resulting in the weak interactions.
文摘The application of biomimetics in the development of unmanned-aerial-vehicles （UAV） has advanced to an exceptionally small scale of nano-aerial-vehicles （NAV）, which has surpassed its immediate predecessor of micro-aerial-vehicles （MAV）, leaving a vast range of development possi- bilities that MAVs have to offer. Because of the prompt advancement into the NAV research devel- opment, the true potential and challenges presented by MAV development were never solved, understood, and truly uncovered, especially under the influence of transition and low Reynolds number flow characteristics. This paper reviews a part of previous MAV research developments which are deemed important of notification; kinematics, membranes, and flapping mechanisms ranges from small birds to big insects, which resides within the transition and low Reynolds number regimes. This paper also reviews the possibility of applying a piezoelectric transmission used to pro- duce NAV flapping wing motion and mounted on a MAV, replacing the conventional motorized flapping wing transmission. Findings suggest that limited work has been done for MAVs matching these criteria. The preferred research approach has seen bias towards numerical analysis as compared to experimental analysis.
基金The project supported by the National Natural Science Foundation of China(10072066,90305009) the Chinese Academy of Sciences(KJCX-SW-L04,KJCX2-SW-L2)
文摘A theoretical modeling approach as well as an unsteady analytical method is used to study aerodynamic characteristics of wing flapping with asymmetric stroke-cycles in connection with an oblique stroke plane during insect forward flight. It is revealed that the aerodynamic asymmetry between the downstroke and the upstroke due to stroke-asymmetrical flapping is a key to understand the flow physics of generation and modulation of the lift and the thrust. Predicted results for examples of given kinematics validate more specifically some viewpoints that the wing lift is more easily produced when the forward speed is higher and the thrust is harder, and the lift and the thrust are generated mainly during downstroke and upstroke, respectively. The effects of three controlling parameters, i.e. the angles of tilted stroke plane, the different downstroke duration ratios, and the different angles of attack in both down- and up-stroke, are further discussed. It is found that larger oblique angles of stroke planes generate larger thrust but smaller lift; larger downstroke duration ratios lead to larger thrust, while making little change in lift and input aerodynamic power; and again, a small increase of the angle of attack in downstroke or upstroke may cause remarkable changes in aerodynamic performance in the relevant stroke.
基金Acknowledgement This research was supported by the National Natural Science Foundation of China （Grant No. 10732030） and the 111 Project （B07009）.
文摘We have examined the aerodynamic effects of corrugation in model wings that closely mimic the wing movements of a forward flight bumblebee using the method of computational fluid dynamics. Various corrugated wing models were tested （care was taken to ensure that the corrugation introduced zero camber）. Advance ratio ranging from 0 to 0.57 was considered. The results shown that at all flight speeds considered, the time courses of aerodynamic force of the corrugated wing are very close to those of the flat-plate wing. The cornlgation decreases aerodynamic force slightly. The changes in the mean location of center of pressure in the spanwise and chordwise directions resulting from the corrugation are no more than 3% of the wing chord length. The possible reason for the small aerodynamic effects of wing corrugation is that the wing operates at a large angle of attack and the flow is separated： the large angle of incidence dominates the corrugation in determining the flow around the wing, and for separated flow, the flow is much less sensitive to wing shape variation.
基金National Natural Science Foundation of China (10732030)"111" Project (B07009)
文摘In this paper, we study the aerodynamic interactions between the contralateral wings and between the body and wings of a model insect, when the insect is hovering and has various translational and rotational motions, using the method numerically solving the Navier-Stokes equations over moving overset grids. The aerodynamic interactional effects are identified by compar-ing the results of a complete model insect, the corresponding wing pair, single wing and body without the wings. Horizontal, vertical and lateral translations and roll, pitch and yaw rotations at small speeds are considered. The results indicate that for the motions considered, both the interaction between the contralateral wings and the interaction between the body and wings are weak. The changes in the forces and moments of a wing due to the contralateral wing interaction, of the wings due to the pres-ence of the body, and of the body due to the presence of the wings are generally less than 4.5%. Results show that aerodynamic forces of wings and body can be measured or computed separately in the analysis of flight stability and control of hovering in-sects.
文摘In the present work, a thorough investigation on the microstructural and morphological aspects of dragonfly wings was carried out using scanning electron microscope. Then, based on this study and the previous reports, a precise three-dimensional numerical model was developed and natural frequencies and vibration modes of dragonfly forewing were determined by finite element method. The results shown that dragonfly wings are made of a series of adaptive materials, which form a very complex composite structure. This bio-composite fabrication has some unique features and potential benefits. Furthermore, the numerical results show that the first natural frequency of dragonfly wings is about 168 Hz and bending is the predominant deformation mode in this stage. The accuracy of the present analysis is verified by comparison of calculated results with experimental data. This paper may be helpful for micro aerial vehicle design concerning dynamic response.
基金The project supported by the National Natural Science Foundation of China(10232010)
文摘The aerodynamic forces and flow structure of a model insect wing is studied by solving the Navier-Stokes equations numerically.After an initial start from rest,the wing is made to execute an azimuthal rotation(sweeping)at a large angle of attack and constant angular velocity.The Reynolds number(Re)considered in the present note is 480(Re is based on the mean chord length of the wing and the speed at 60% wing length from the wing root).During the constant-speed sweeping motion,the stall is absent and large and approximately constant lift and drag coefficients can be maintained.The mechanism for the absence of the stall or the maintenance of large aerodynamic force coefficients is as follows.Soon after the initial start,a vortex ring,which consists of the leading-edge vortex(LEV),the starting vortex,and the two wing-tip vortices,is formed in the wake of the wing.During the subsequent motion of the wing,a base-to-tip spanwise flow converts the vorticity in the LEV to the wing tip and the LEV keeps an approximately constant strength.This prevents the LEV from shedding.As a result, the size of the vortex ring increases approximately linearly with time,resulting in an approximately constant time rate of the first moment of vorticity,or approximately constant lift and drag coefficients. The variation of the relative velocity along the wing span causes a pressure gradient along the wing- span.The base-to-tip spanwise flow is mainly maintained by the pressure-gradient force.
