Numerical modeling and application of the effects of fish movement on flow field in recirculating aquaculture system

Hydrodynamics plays a crucial role in the recirculating aquaculture system (RAS). An efficient flow field is essential for removing residual bait and feces, creating a healthy environment for fish growth, development, and overall welfare. Hydrodynamics not only influences fish growth and development, but the presence and movement of fish also impact the flow dynamics within the culture tank. This article proposes a fluid-solid coupled model based on computational fluid dynamics (CFD) to investigate the interaction between fish movement and the flow field. Firstly, we established a numerical model of a circular tank using tetrahedral meshing. Several bionic fish were introduced into the tank simultaneously, and their movements were defined using UDF (User-Defined Function) files. Secondly, we evaluated the effects of different numbers of fish movements on the velocity and uniformity of the flow field within the tank. To quantitatively analyze the impact of different numbers of bionic fish on the flow field in the culture tank, we calculated the average velocity, velocity uniformity coefficients, and energy-effective utilization coefficients in three different planes (Y = 0.05, Y = 0.1, and Y = 0.15). This study demonstrated that the presence of fish and their tail-swinging motion enhanced the stability of the flow field and reduced low flow velocity zones in the culture tank. As the number of fish increased, the velocity significantly decreased, and the velocity uniformity decreased as well. The results highlight the effectiveness of the numerical modeling method for the fluid-solid coupling of fish interactions with the system's flow field. Furthermore, the model aligns with experimental results and can be utilized to study fish movement and flow fields effectively.