Numerical Study On The Self-propelled Swimming Of Bionic Fish Propelled By Caudal Fin And Pectoral Fin

The fish,as a kind of aquatic organisms,is an excellent swimmer after long-term evolution and natural selection.The fish based on thunniform mode can cruise for a long distance with fast speed and high efficiency.The fish based on labriform mode has excellent maneuverability,which can perform hovering,retreating,snorkeling and turning.All these advantages of fish are the design goals pursued by underwater vehicles.The propulsion-maneuvering system resorting to propellers and rudders has greatly restricted the operational capabilities of underwater vehicles for its large size,low efficiency and poor maneuverability.Therefore,the design of bionic propeller and robotic fish has been studied by scholars with a focus on understanding the mechanism of fish swimming.In this paper,a 3-DoF self-propelled swimming method of fish was established based on CFD method and dynamic mesh method,so as to study the hydrodynamic performance of the bionic fish in different body shapes and motion modes.Major contributions of this paper are presented as follows:The process of solving the hydrodynamic performance of the fish-like body based on the RANS equation and the dynamic mesh method was introduced.The mesh division strategy that is applicable for solving this problem was given with the NACA0012 hydrofoil.It also studied the mesh convergence and verify the calculation method by comparing the numerical and experimental values in literatures.A bionic fish 3-DoF self-propelled swimming procedure compiled through the secondary development of CFD software FLUENT was compared with the results of the bionic fish in the uniform flow and the self-propelled swimming results of bionic fish in literatures,verifying the reliability of the calculation method.Three caudal fin models were constructed in accordance with the tail fins of tuna,dolphin and whale,which contributed to not only studying the forward speed,longitudinal force,power and propulsion efficiency of bionic fish,but also analyzing the influence of the shape change of the trailing edge on the fast cruise and long-distance cruise of bionic fish.The numerical pectoral fin was set up under the labriform mode.Moreover,the motion model of the pectoral fin in the drag mode and the lift mode were given.These two motion models were adopted in studying the directional swimming and rotational swimming of the bionic fish.The forward speed during the directional swimming were discussed,and the mechanism of the pectoral fin from the surface pressure and the vortex structure.Further,the motion trajectories of fish during the rotational motion under two motion modes were discussed.Finally,the numerical model was established for the bionic fish under the joint propulsion of the pectoral fin and the tail fin.The bionic fish swims forward under the propulsion of the tail fin,while the swimming direction is intermittently adjusted by the pectoral fin adopting the resistance mode and the lift mode,respectively.The swimming speed and trajectory of bionic fish were studied,and the vortex structure during the direction adjustment were given.According to the findings,it is feasible to study the self-propelled swimming of fish in different body shapes and motion modes using CFD method.Also,the calculated results are reasonable and effective.The research methods used in this paper can provide a theoretic basis and reference for the research and development of the bionic robotic fish.