Research On Flow Field Characteristics Of Oscillating Caudal Fin Based On DPIV Technology

Surface and underwater vehicles have been adopted to explore and utilize the deep-sea natural source. Underwater vehicles have played important roles in military undersea survey, submarine sampling, information gathering and other engineering projects. As a new type of underwater propulsion and maneuvering systems, fish-like propulsion technology has drawn more and more attention. This technology has turned into an important research direction with advantages of fast, efficient, flexible, quiet, etc.Fish gets great thrust force with optimal control of vortex shedding as wake vorticity is generated downstream from the boundary layer. It's significant to research into the vortex evolvement (forming, developing, shedding) and trailing vortex structure for understanding locomotory mechanism of fish. Oscillating plate promotion mode is adopted in the paper which investigates the flow field of flexible oscillating caudal fin based on DPIV technology. The effects of different caudal fin model on the structure of vortex field are analyzed. We construct computation module of hydrodynamic performance referring to flow field information, and meanwhile conduct hydrodynamic measurement and analysis.Singal control that flow field captured under series oscillating angle of caudal fin is realized primarily combined with encoder, PLC and DPIV technology. This attempt for DPIV external triggering provides reliable data and information of flow field. Then the structure and evolvement of wake vorticity in unsteady flow field are analyzed, with mention of the effects of various hydrodynamic parameters (the height of light sheet, oscillating position, oscillating frequency, freestream velocity, oscillating amplitude, St, flexibility and etc). It concludes that flexible foil can get better rectifying effect and higher efficiency in specific cases. Optimal matching for parameters of caudal fin is analyzed, and maximal thrust occurs as St is about 0.47.3D vortex ring is reconstructed based on flow field information, and a method of solving velocity circulation, momentum and hydrodynamic force are studied. Finally, to research on the hydrodynamic force acting on the caudal fin model, we design three-component balance, and measure the force and torque on the oscillating caudal fin, which provides a method to measure force and moment in the flow field.