Spanwise flexibility is a key factor influencing propulsion performance of pectoral foils. Performances of bionic fish with oscillating pectoral foils can be enhanced by properly selecting the spanwise flexibility. Th...Spanwise flexibility is a key factor influencing propulsion performance of pectoral foils. Performances of bionic fish with oscillating pectoral foils can be enhanced by properly selecting the spanwise flexibility. The influence law of spanwise flexibility on thrust generation and propulsion efficiency of a rectangular hydro-foil is discussed. Series foils constructed by the two-component silicon rubber are developed. NACA0015 shape of chordwise cross-section is employed. The foils are strengthened by fin rays of different rigidity to realize variant spanwise rigidity and almost the same chordwise flexibility. Experiments on a towing platform developed are carried out at low Reynolds numbers of 10 000, 15 000, and 20 000 and Strouhal numbers from 0.1 to 1. The following experimental results are achieved: (1) The average forward thrust increases with the St number increased; (2) Certain degree of spanwise flexibility is beneficial to the forward thrust generation, but the thrust gap is not large for the fins of different spanwise rigidity; (3) The fin of the maximal spanwise flexibility owns the highest propulsion efficiency; (4) Effect of the Reynolds number on the propulsion efficiency is significant. The experimental results can be utilized as a reference in deciding the spanwise flexibility of bionic pectoral fins in designing of robotic fish prototype propelled by flapping-wing.展开更多
This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical...This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign（positive or negative） of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of ＂bow＂ and the fin surface of ＂scoop＂. It is observed that for both the fin surface of ＂bow＂ and the fin surface of ＂scoop＂, the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of ＂bow＂, the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of ＂scoop＂ can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.展开更多
The hydrodynamic performance of the virtual underwater vehicle under self-yaw is investigated numerically in this paper,we aim to explore the fluid laws behind this plane motion achieved by the bionic flexibility,espe...The hydrodynamic performance of the virtual underwater vehicle under self-yaw is investigated numerically in this paper,we aim to explore the fluid laws behind this plane motion achieved by the bionic flexibility,especially the spanwise flexibility of the caudal fin.The kinematics of the chordwise flexible body and the spanwise flexible caudal fin are explored through dynamic mesh technology and user-defined functions(UDF).The 3-D Navier-Stokes equations are applied to simulate the viscid fluid surrounding the bionic dolphin.The study focuses on quantitative problems about the fluid dynamics behind the specific motion law,including speed of movement,energy loss and working efficiency.The current results show that the self-yaw can be composed of two motions,autonomous propulsion and active steering.In addition,the degree of the flexible caudal fin can produce different yaw effects.The chordwise phase differenceФis dominant in the propulsion function,while the spanwise phase differenceδhas a more noticeable effect on the steering function.The pressure distribution on the surface of the dolphin and the wake vortex generated in the flow field reasonably reveal the evolution of self-yaw.It properly turns out that the dolphin can combine the spanwise flexible caudal fin and the chordwise flexible body to achieve self-yaw motion.展开更多
基金supported by National Hi-tech Research and Development Program of China(863 Program, Grant No. 2006AA04Z252)National Natural Science Foundation of China(Grant No. 51005006)+1 种基金Research Fund for the Doctoral Program of Higher Education of China(Grand No. 20101102110022)Innovation Foundation of Beihang University for PhD Graduates, China
文摘Spanwise flexibility is a key factor influencing propulsion performance of pectoral foils. Performances of bionic fish with oscillating pectoral foils can be enhanced by properly selecting the spanwise flexibility. The influence law of spanwise flexibility on thrust generation and propulsion efficiency of a rectangular hydro-foil is discussed. Series foils constructed by the two-component silicon rubber are developed. NACA0015 shape of chordwise cross-section is employed. The foils are strengthened by fin rays of different rigidity to realize variant spanwise rigidity and almost the same chordwise flexibility. Experiments on a towing platform developed are carried out at low Reynolds numbers of 10 000, 15 000, and 20 000 and Strouhal numbers from 0.1 to 1. The following experimental results are achieved: (1) The average forward thrust increases with the St number increased; (2) Certain degree of spanwise flexibility is beneficial to the forward thrust generation, but the thrust gap is not large for the fins of different spanwise rigidity; (3) The fin of the maximal spanwise flexibility owns the highest propulsion efficiency; (4) Effect of the Reynolds number on the propulsion efficiency is significant. The experimental results can be utilized as a reference in deciding the spanwise flexibility of bionic pectoral fins in designing of robotic fish prototype propelled by flapping-wing.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51875101,51375085)
文摘This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign（positive or negative） of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of ＂bow＂ and the fin surface of ＂scoop＂. It is observed that for both the fin surface of ＂bow＂ and the fin surface of ＂scoop＂, the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of ＂bow＂, the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of ＂scoop＂ can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.
基金This work was supported by National Natural Science Founda-tion of China[grant number 51875101]State Key Laboratory of Robotics and System(HIT)[grant number SKLRS-2018-KF-11].
文摘The hydrodynamic performance of the virtual underwater vehicle under self-yaw is investigated numerically in this paper,we aim to explore the fluid laws behind this plane motion achieved by the bionic flexibility,especially the spanwise flexibility of the caudal fin.The kinematics of the chordwise flexible body and the spanwise flexible caudal fin are explored through dynamic mesh technology and user-defined functions(UDF).The 3-D Navier-Stokes equations are applied to simulate the viscid fluid surrounding the bionic dolphin.The study focuses on quantitative problems about the fluid dynamics behind the specific motion law,including speed of movement,energy loss and working efficiency.The current results show that the self-yaw can be composed of two motions,autonomous propulsion and active steering.In addition,the degree of the flexible caudal fin can produce different yaw effects.The chordwise phase differenceФis dominant in the propulsion function,while the spanwise phase differenceδhas a more noticeable effect on the steering function.The pressure distribution on the surface of the dolphin and the wake vortex generated in the flow field reasonably reveal the evolution of self-yaw.It properly turns out that the dolphin can combine the spanwise flexible caudal fin and the chordwise flexible body to achieve self-yaw motion.
