Analysis Of Hydrodynamic Characteristics Of Juvenile Grass Carp (Ctenopharyngodon Idellus) Under Different Swimming Modes

The study of fish swimming mechanism has important significance and necessity.On the one hand,the problem itself contains a wealth of unrevealed mechanical mechanisms.Research results in this field can guide the development and development of new high-performance underwater vehicles.At the same time,it can also promote the ecological protection of fish.On the other hand,with the enrichment and accuracy of research methods,more and more research work pays more attention to the differences in fish swimming patterns,the role of various parts of the fish body in promoting the advancement of fish and efficient swimming,and It is similar to the specific swimming mode adopted to adapt to the surrounding flow field and the active control of the surrounding fluid.In this paper,the typical swaying fish species-grass carp juveniles(Ctenopharyngodon idellus)are used as the research object.Particle Image Velocimetry is used to obtain the instantaneous flow field data and vorticity around the juveniles,and then the direct integration method is used to reconstruct them.The pressure distribution of the fluid around the juvenile fish,based on the theory of fish swimming dynamics based on the pressure field,the movement of the grass carp juveniles whose body length varies within the range of 4?10cm in the three swimming modes of cruise,tail-sliding and turning Corresponding research has been done on the characteristics of science and dynamics,quantified the thrust,resistance and formation positions of the juvenile grass carp in different swimming modes,and analyzed the mechanical mechanism of the interaction between the fish and the flow field.The main research work and conclusion as below:(1)Through the PIV technology,the instantaneous flow field structure information of the juvenile grass carp in the three swimming modes of cruise,tail-sliding and turning was obtained,and the vorticity and pressure distribution of grass carp juveniles in different swimming modes were analyzed.The results show that: under the three swimming modes,there will be positive pressure zones on the snout and tail of the juvenile fish body,but there are obvious differences in the structure of the tail vortex of the fish body.In the cruise swimming mode,the juvenile grass carp passes through the fish.The body swing will form constant shedding vortices on both sides of the tail,while the vortices formed in the tail-sliding and turning swimming modes are distributed on the right side of the fish body.(2)By quantifying the pressure distribution of grass carp juveniles,the thrust and resistance generated by the positive and negative fluid pressures and their proportions were calculated,and the role of positive and negative fluid pressures in fish swimming was clarified.The results show that the thrust of the fish body by the surrounding fluid in the cruise swimming mode and its changing trend over time depend on the distribution of positive pressure around the juvenile fish,and the negative pressure around the fish body determines the resistance during the movement of the juvenile fish;The amount of fluid thrust and resistance received by the fish in tail-swimming and turning swimming modes depends on the negative pressure distribution around the body.In general,the positive fluid pressure is more conducive to the cruising of grass carp juveniles,while the negative fluid pressure is more conducive to the tailsliding and turning of the juveniles.(3)By calculating the distribution characteristics of thrust and resistance along the length of the fish body,the main role of the head,middle and tail of the fish body in the process of thrust formation is verified.The results show that: swimming in cruise,tail-swimming-sliding and turning In the mode,thrust is generated at all parts of the fish body,but the most concentrated thrust is at the tail(63.74?N),which proves that the tail is the main source of power for the juvenile grass carp,and the middle part of the fish body is the main part of resistance.(4)By comparing the swimming efficiency of the three swimming modes,the internal reasons why grass carp juveniles choose different swimming modes are analyzed.The results show that the maximum efficiency of cruise swimming reaches 70.35±21.84%,followed by tail-swimming swimming,which reaches 64.47±22.06%,while the efficiency of turning swimming is the lowest 40.85±28.35%.It is speculated that grass carp juveniles choose different swimming modes to cope with their different biological needs.For cruising,especially during long-term migration and migration,low energy consumption And high efficiency is important,and for motorized swimming such as tail-swimming and turning swimming,high maneuverability is even more important.