Abstract
Aloach has unique propulsion technique by bending its long body and using its tail fin. Its motion and flow around it have been experimentally visualized by particle image velocimetry (PIV). Generating and growing vortices by bending its body, it pushes water backward to gain repulsing force. After moving forward it leaves a vortex street like reverse Karman vortices which means loach gains propulsion. Vortex structure around tail fin is also studied in both horizontal and vertical cross section. Furthermore, flow field in direction change is also studied and large vortex at the side of the head is shown.
