Affiliations: Dept. of Mechanical and Information Science and
Technology, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka, Fukuoka,
820-8502, Japan. E-mail: nagayama@mse.kyutech.ac.jp | Dept. of Mechanical and Information Science and
Technology, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka, Fukuoka,
820-8502, Japan
Abstract: The propulsion methods of the aquatic lives are the results of
optimization by evolution and are useful for the design of swimming-robot, etc.
Among them, loach has unique propulsion technique both bending its long body
and shaking caudal fin. Our purpose of the research is to clarify its swimming
mechanism through flow field analysis. Two dimensional motion and flow around
it have been experimentally visualized by particle image velocimetry (PIV).
Vortices around a loach and the interactions between the loach body and
surrounding water are analyzed. Generating and growing vortices by bending its
body, it pushes water backward to gain repulsing force, and it seems that moves
through vortices reducing the resistance force at the same time. When a vortex
reaches to the caudal fin, it accelerates both sides of the vortex pushing
water backward and seems gaining propulsion utilizing the caudal fin. After
moving forward, loach leaves a vortex street like reverse Karman vortices,
which means that loach gains propulsion.
