Hydrodynamic Research And Design Of Flapping Wing Fish

With the proposal of the 14 th five year plan for marine economic development,marine equipment such as underwater robots is of great significance for resource exploration and utilization.Among them,flapping wing motion mode with large deformation motion characteristics can effectively improve the mobility of robotic fish,which is a research hotspot of underwater robot.This kind of motion refers to simulating the fish median / double fin motion mode to obtain better propulsion efficiency and complete special actions such as hovering and steering.Compared with the traditional rigid structure,it has better fluid performance,less fluid disturbance and broad application prospects.Based on the flapping wing motion mode of manta rays and the hydrodynamics of fish motion,combined with the flexible driving mode and the large deformation motion theory of fish body,this paper uses the finite element simulation method to study the motion hydrodynamics and vortex structure evolution of the underwater flapping wing structure model driven by software,The hydrodynamic performance of flapping wing motion and the interaction between vortex and flapping wing tail vortex in unsteady flow field are analyzed.The following results were obtained:1.Analyzing and comparing the effects of different structural performance,the optimal structure is established;this paper uses the finite element simulation method to study the motion hydrodynamics and vortex structure evolution of the underwater flapping wing structure model driven by software,and chord motion for mathematical description respectively.2.The finite element model is established,and the spanwise motion and chord motion are simulated and calculated respectively.The swing analysis of the flexible actuator simulating the fin structure is carried out to obtain the motion parameters;According to the actual water area attribute parameters of the biological prototype,combined with the dynamic grid technology,the lift characteristics of large deformation motion under the influence of different driver driving frequencies are analyzed:(1)The M-type actuator structure with semicircular section and diameter thickness ratio of 0.8 ～ 1.4 can produce a wide range of bending motion under low input and has small radial expansion deformation,which basically does not affect the hydrodynamic characteristics of the moving structure,and its swing characteristics are consistent with the existing biological observation structures.(2)By adjusting the input frequency of the driver,the pectoral fin can obtain different deflection phase angles of the front and rear edge structure to obtain better lift characteristics.The lower pectoral fin structure corresponding to the driving frequency of0.8hz has better lift performance;Adjust the driving frequency corresponding to the flapping wing motion frequency to make the pectoral fin produce periodic thrust changes.(3)In the steady flow of the integral mode model,the movement of the flapping wing tip is approximately a sinusoidal function,the amplitude is about 0.12 M,the overall movement speed is 0.46m/s,and its Strouhal number is 0.26,which is in line with the movement range of aquatic organisms using flapping wing movement.3.In view of the phenomenon that various obstacles and the interaction between fish will lead to fluid disturbance in the actual water area,while the real fish can still obtain high-efficiency and high-speed swimming ability in this environment.The hydrodynamic characteristics of flapping wing motion under unsteady flow conditions are studied by selecting the fluid disturbance generated by the flow around a fixed cylinder and the flow around a simple harmonic cylinder and the interaction in the formation motion mode:(1)By calculating the Strouhal number under different working conditions,the optimal motion parameters are evaluated,that is,the simple harmonic motion cylinder radius is 5mm,the motion amplitude is 10 mm,and the Karman vortex street can be generated under the condition of motion frequency 1Hz.(2)The thrust coefficient and propulsion efficiency of the flapping wing are studied and analyzed respectively.Under the motion conditions,when the distance is twice the ratio,the highest propulsion efficiency can be obtained,up to twice the movement of the single flapping wing,Under the condition of the lowest propulsion efficiency,that is,the spacing is 4.5 times of the cylinder radius,it can still reach about1.1 times of the single flapping wing movement.(3)It is found that in the complete motion cycle,the front wing will affect the formation of the rear wing vortex.When the spacing is too large,it is similar to the influence of the simple harmonic cylinder on the rear wing;In the state of low spacing,the rear wing will absorb the vortex falling off the front wing,resulting in the vortex generated by the front wing will continue to move until the root of the rear wing begins to fall off to form a vortex street,that is,the two wings are regarded as a whole in the generation and evolution process of vortex structure,which can effectively reduce the motion resistance of the rear wing.Due to the different deflection angle of the two wings and the motion direction of the falling vortex at a specific time,The opposite rotation direction produces interference,and the front wing interferes with the rear wing,but the influence on the complete flapping wing motion cycle is low.In this paper,the research on flapping wing motion mode is explored from flexible drive to hydrodynamic characteristics,which provides ideas and directions for the application of flexible drive to large deformation flapping wing motion.In view of flapping wing motion in unsteady motion environment,it is proved that flapping wing motion mode can effectively reduce its own energy consumption in actual water environment compared with traditional propulsion structure,Obtain good hydrodynamic characteristics;It has the same excellent drag reduction efficiency as other fish queues,can effectively reduce energy consumption,and is conducive to the development and design of bionic robotic fish with flapping wing movement mode.It has important theoretical and engineering value.