A Numerical Study Of Tadpole Swimming Behind A Blunt Body

The living environment of aquatic animals is complicated and everchanging.There are always vortices in nature.According to researches,aquatic animals are usually expert in taking advantages of the surrounding vortices.By adjusting the body to control the flow around,aquatic animals are able to improve swimming abilities.There are many experimental and numerical researches about how fish extract energy from environmental vortices.However,much less is known about the interaction between the tadpole and its surroundings.The results show that the tadpole undulating in the wake of a blunt body is able to gain thrust from pressure difference between tadpole’s head and tail,the local reverse flow on both sides of tadpole and the local backward jet in the wake.For a 2-D tadpole swimming in the wake of a D-cylinder,the swimming of the tadpole can be divided into: the dodging mode,the breaking mode and the mixed mode at different undulating frequencies.As the distance between the D-cylinder and tadpole changes,three different flow structures are observed,such as no vortex street in the wake of Dcylinder,Kármán vortex street between the D-cylinder and the tadpole and incomplete Kármán vortex street between the D-cylinder and the tadpole.As the diameter of the D-cylinder changes,the shedding frequency of the D-cylinder and the width of the Kármán vortex street also change,which influence the flow field.For a 3-D tadpole swimming in the wake of a ball,the flow field is different from that of 2-D cases.Vortices shed from the ball are broken into two parts by the tadpole’s head and go directly into the wake of the tadpole without staying on the tail of the tadpole.