The Influence Of Fish Movement On Flow Field In Recirculating Aquaculture Tank Studied Based On CFD

Recirculating aquaculture systems(RAS)is a new aquaculture model that integrates modernization,automation and intensification.Water is one of the most important environmental factors in a recirculating aquaculture system,and its flow and water quality can directly affect the growth quality of fish,while the presence and movement of fish also affect the flow field in the aquaculture tank,which in turn affects the performance of dissolved oxygen and sewage in the aquaculture tank.At present,scholars at home and abroad have done a lot of research on the hydrodynamic characteristics of recirculating water aquaculture tanks based on geometric design and the number of daily cycles,but little attention has been paid to the influence of the presence and movement of fish on the flow field in aquaculture tanks,and the few studies on the flow field characteristics of aquaculture tanks and the influence of fish are mainly based on the actual measurement methods.Few studies have used numerical simulation methods to reveal the influence of cultured fish on the flow field in culture tanks.In order to study the influence of the presence of fish and their motion on the flow field characteristics in the culture tank,this paper uses CFD(computational fluid dynamics)method to establish a numerical model of fish-flow field coupling,and defines the tail-wagging motion of the bionic fish in the culture tank by writing UDF macro files,and simulates the influence of fish motion on the flow field in the culture tank as time advances based on dynamic grid technology.The main findings of this study are as follows.(1)The bionic fish models established by using CAD,Solidworks and other software can share and exchange numerical models with ANSYS directly through the software interface,and the UDF macro file written based on the trevally fluctuation equation can be used to define the tail fin motion of the bionic fish in two-dimensional plane and three-dimensional space,and because the equation of motion is universal,it is possible to define any kind of fish based on the correstanking fish model The equations of motion are universal,so any kind of bionic fish motion can be defined based on the correstanking fish model.The oscillation of the fish tail in the two-dimensional plane will cause pressure and velocity differences in the surrounding flow field,and the oscillation of the tail fin of the bionic fish in the three-dimensional culture tank will form a series of circular shedding vortices at the end of the tail,which will collide with the surrounding water and cause energy consumption,and then affect the flow field in the culture tank.(2)In order to verify the accuracy of the numerical model,the experiments were conducted by fixing the fish in the tank and measuring the lateral force of the fish when it swings its tail through the sensor,and a numerical model of fish-flow field coupling was established according to the 1:1 model,and the error between the experimentally measured lateral force of the fish and the numerical simulation was within the permissible range,which can be used for the subsequent study of the effect of fish motion on the hydrodynamics of the aquaculture tank.(3)The presence of fish and their tail-swing motion can have a significant effect on the hydrodynamic conditions around them.The energy generated by the motion of low-density culture fish is small and insufficient to change the average velocity in the culture tank.The energy generated by the continuous tail swing will destroy the velocity field around the wall of the aquaculture tank;the effective energy utilization coefficient in the aquaculture tank has a certain positive correlation with the uniformity of the flow field,which is not proportional to the number of bionic fish in the tank,and a suitable aquaculture density can optimize the hydrodynamic conditions in the aquaculture tank.(4)The effect of fish movement with different tail swinging frequencies on the flow field in the tank varies.The increase of tail swinging frequency has the most obvious effect on the flow field in the square round corner aquaculture tank,dispersing the low flow velocity area in the square round corner tank,increasing the average flow velocity and flow field uniformity in the aquaculture tank,and the round aquaculture tank has good uniformity.3Hz also improved the average velocity and uniformity in the tank.