Insects usually fly by passively rotating wings,which has been applied to the design of flapping-wing Micro-Air Vehicles(MAVs)to reduce mechanical complexity.In this paper,a robotic passive rotating-wing model is desi...Insects usually fly by passively rotating wings,which has been applied to the design of flapping-wing Micro-Air Vehicles(MAVs)to reduce mechanical complexity.In this paper,a robotic passive rotating-wing model is designed to investigate wing kinematics and lift generation,which are measured by a high-speed camera and a force transducer,respectively.In addition,flow fields are measured using the Particle Image Velocimetry(PIV).Experimental results demonstrate that passive rotating motion has a coordinative relationship with actively stroking motion.As the stroke amplitude or frequency increases,the rotating amplitude is enlarged.To characterize the active stroking motion,a driving Reynolds number Redrivingis defined,which varies from 68 to 366 in this study.Moving the gravity center of the wing towards trailing ed ge induces the increase of additional torque M,which decreases the wing rotating amplitude and promotes the advance of wing rotation.We find that the timing of wing rotation is gradually delayed and the mean lift coefficient C^(-)_(L)monotonously decreases as Redrivingincreases.By increasing the additional torque M,C^(-)_(L)is slightly improved and approaches to the lift coefficient of a real fruit fly at driving Re approximately equal to 230.The instantaneous lifts combined with the vortical structures further demonstrate that the lift generation associated with wing rotation is mainly attributed to the growth of the LeadingEdge Vortex(LEV)and the passive wake capture mechanism.Passive wake capture is influenced by LEV,reversal stroke motion and wing additional torque together,which can only maintain the lift at a high level for a considerable period.The high-lift generation mechanisms of flapping and passive rotating flight could shed light on the simplified design of MAVs and the improvement of their aerodynamic performance.展开更多
Flapping-powered propulsion is used by many animals to locomote through air or water. Here we review recent experimental and numerical studies on self-propelled mechanical systems powered by a flapping motion. These s...Flapping-powered propulsion is used by many animals to locomote through air or water. Here we review recent experimental and numerical studies on self-propelled mechanical systems powered by a flapping motion. These studies improve our understanding of the mutual interaction between actively flapping bodies and surrounding fluids. The results obtained in these works provide not only new insights into biolocomotion but also useful information for the biomimetic design of artificial flyers and swimmers.展开更多
Propulsive performance of a passively flapping plate in a uniform viscous flow has been studied numerically by means of a multiblock lattice Boltzmann method. The passively flapping plate is modeled by a rigid plate w...Propulsive performance of a passively flapping plate in a uniform viscous flow has been studied numerically by means of a multiblock lattice Boltzmann method. The passively flapping plate is modeled by a rigid plate with a torsion spring acting about the pivot at the leading-edge of the plate, which is called a lumped-torsional-flexibility model. When the leading-edge is forced to take a vertical oscillation, the plate pitches passively due to the fluid-plate interaction. Based on our numerical simulations, various fundamental mechanisms dictating the propulsive performance, including the forces on the plate, power consumption, propulsive efficiency and vortical structures, have been studied. It is found that the torsional flexibility of the passively pitching plate can improve the propulsive performance. The results obtained in this study provide some physical insights into the understanding of the propulsive behaviors of swimming and flying animals.展开更多
The direct-forcing fictitious domain method is extended to simulate the locomotion of a passively pitching foil. Our study focuses on the hysteresis phenomenon that the critical frequency for the reverse of the locomo...The direct-forcing fictitious domain method is extended to simulate the locomotion of a passively pitching foil. Our study focuses on the hysteresis phenomenon that the critical frequency for the reverse of the locomotion direction of the wing in case of decreasing frequency is smaller than that in case of increasing frequency. In our simulations, the hysteresis phenomenon is produced by imposing different initial conditions at a same frequency. Our results indicate that the ratio of the heaving amplitudes of two foil edges is crucial to the direction of the foil＇s horizontal motion, and the amplitude of the leading edge is generally smaller. The critical frequencies for the reverse of the locomotion direction are increased, when the foil-fluid density ratio is decreased or the spring constant is increased. The critical frequencies in the bi-stability regime also depend on the initial velocity imposed, and the hysteresis loop generally becomes larger if the initial velocities are closer to the terminal locomotion velocities of the foil.展开更多
The analysis of the passive rotation feature of a micro Flapping Rotary Wing（FRW）applicable for Micro Air Vehicle（MAV） design is presented in this paper. The dynamics of the wing and its influence on aerodynamic p...The analysis of the passive rotation feature of a micro Flapping Rotary Wing（FRW）applicable for Micro Air Vehicle（MAV） design is presented in this paper. The dynamics of the wing and its influence on aerodynamic performance of FRW is studied at low Reynolds number（~10~3）.The FRW is modeled as a simplified system of three rigid bodies： a rotary base with two flapping wings. The multibody dynamic theory is employed to derive the motion equations for FRW. A quasi-steady aerodynamic model is utilized for the calculation of the aerodynamic forces and moments. The dynamic motion process and the effects of the kinematics of wings on the dynamic rotational equilibrium of FWR and the aerodynamic performances are studied. The results show that the passive rotation motion of the wings is a continuous dynamic process which converges into an equilibrium rotary velocity due to the interaction between aerodynamic thrust, drag force and wing inertia. This causes a unique dynamic time-lag phenomena of lift generation for FRW, unlike the normal flapping wing flight vehicle driven by its own motor to actively rotate its wings. The analysis also shows that in order to acquire a high positive lift generation with high power efficiency and small dynamic time-lag, a relative high mid-up stroke angle within 7–15° and low mid-down stroke angle within -40° to -35° are necessary. The results provide a quantified guidance for design option of FRW together with the optimal kinematics of motion according to flight performance requirement.展开更多
基金supported by the National Nature Science Foundation of China(Nos.12102259,12202273)the China Postdoctoral Science Foundation(No.2018M642007)。
文摘Insects usually fly by passively rotating wings,which has been applied to the design of flapping-wing Micro-Air Vehicles(MAVs)to reduce mechanical complexity.In this paper,a robotic passive rotating-wing model is designed to investigate wing kinematics and lift generation,which are measured by a high-speed camera and a force transducer,respectively.In addition,flow fields are measured using the Particle Image Velocimetry(PIV).Experimental results demonstrate that passive rotating motion has a coordinative relationship with actively stroking motion.As the stroke amplitude or frequency increases,the rotating amplitude is enlarged.To characterize the active stroking motion,a driving Reynolds number Redrivingis defined,which varies from 68 to 366 in this study.Moving the gravity center of the wing towards trailing ed ge induces the increase of additional torque M,which decreases the wing rotating amplitude and promotes the advance of wing rotation.We find that the timing of wing rotation is gradually delayed and the mean lift coefficient C^(-)_(L)monotonously decreases as Redrivingincreases.By increasing the additional torque M,C^(-)_(L)is slightly improved and approaches to the lift coefficient of a real fruit fly at driving Re approximately equal to 230.The instantaneous lifts combined with the vortical structures further demonstrate that the lift generation associated with wing rotation is mainly attributed to the growth of the LeadingEdge Vortex(LEV)and the passive wake capture mechanism.Passive wake capture is influenced by LEV,reversal stroke motion and wing additional torque together,which can only maintain the lift at a high level for a considerable period.The high-lift generation mechanisms of flapping and passive rotating flight could shed light on the simplified design of MAVs and the improvement of their aerodynamic performance.
基金supported by the Chinese Academy of Sciences (Grants KJCX-SW-L08, KJCX3-SYW-S01)the National Natural Science Foundation of China (Grants 11021262, 11023001, 11232011, 11372331)
文摘Flapping-powered propulsion is used by many animals to locomote through air or water. Here we review recent experimental and numerical studies on self-propelled mechanical systems powered by a flapping motion. These studies improve our understanding of the mutual interaction between actively flapping bodies and surrounding fluids. The results obtained in these works provide not only new insights into biolocomotion but also useful information for the biomimetic design of artificial flyers and swimmers.
基金Project supported by the Natural Science Foundation of China(Grant No.11372304)the 111 Project(Grant No.B07033)
文摘Propulsive performance of a passively flapping plate in a uniform viscous flow has been studied numerically by means of a multiblock lattice Boltzmann method. The passively flapping plate is modeled by a rigid plate with a torsion spring acting about the pivot at the leading-edge of the plate, which is called a lumped-torsional-flexibility model. When the leading-edge is forced to take a vertical oscillation, the plate pitches passively due to the fluid-plate interaction. Based on our numerical simulations, various fundamental mechanisms dictating the propulsive performance, including the forces on the plate, power consumption, propulsive efficiency and vortical structures, have been studied. It is found that the torsional flexibility of the passively pitching plate can improve the propulsive performance. The results obtained in this study provide some physical insights into the understanding of the propulsive behaviors of swimming and flying animals.
基金Project supported by the National Natural Science Foun-dation of China(Grant No.11372275)the Program for New Century Excellent Talents in University
文摘The direct-forcing fictitious domain method is extended to simulate the locomotion of a passively pitching foil. Our study focuses on the hysteresis phenomenon that the critical frequency for the reverse of the locomotion direction of the wing in case of decreasing frequency is smaller than that in case of increasing frequency. In our simulations, the hysteresis phenomenon is produced by imposing different initial conditions at a same frequency. Our results indicate that the ratio of the heaving amplitudes of two foil edges is crucial to the direction of the foil＇s horizontal motion, and the amplitude of the leading edge is generally smaller. The critical frequencies for the reverse of the locomotion direction are increased, when the foil-fluid density ratio is decreased or the spring constant is increased. The critical frequencies in the bi-stability regime also depend on the initial velocity imposed, and the hysteresis loop generally becomes larger if the initial velocities are closer to the terminal locomotion velocities of the foil.
文摘The analysis of the passive rotation feature of a micro Flapping Rotary Wing（FRW）applicable for Micro Air Vehicle（MAV） design is presented in this paper. The dynamics of the wing and its influence on aerodynamic performance of FRW is studied at low Reynolds number（~10~3）.The FRW is modeled as a simplified system of three rigid bodies： a rotary base with two flapping wings. The multibody dynamic theory is employed to derive the motion equations for FRW. A quasi-steady aerodynamic model is utilized for the calculation of the aerodynamic forces and moments. The dynamic motion process and the effects of the kinematics of wings on the dynamic rotational equilibrium of FWR and the aerodynamic performances are studied. The results show that the passive rotation motion of the wings is a continuous dynamic process which converges into an equilibrium rotary velocity due to the interaction between aerodynamic thrust, drag force and wing inertia. This causes a unique dynamic time-lag phenomena of lift generation for FRW, unlike the normal flapping wing flight vehicle driven by its own motor to actively rotate its wings. The analysis also shows that in order to acquire a high positive lift generation with high power efficiency and small dynamic time-lag, a relative high mid-up stroke angle within 7–15° and low mid-down stroke angle within -40° to -35° are necessary. The results provide a quantified guidance for design option of FRW together with the optimal kinematics of motion according to flight performance requirement.
