Hydrodynamic Of Typical Recirculating Aquaculture Tanks

With the increasingly tense land resources and environmental pollution,aquaculture is bound to move towards energy-saving,emission reduction,ecological and efficient recycling aquaculture mode.The circulating aquaculture of tank is an ecological aquaculture mode that integrates circulating water aquaculture technology,biological water purification technology and efficient collection of sewage or sewage technology.Industrial circulating aquaculture is an automatic aquaculture mode which integrates oxygen enrichment,filtration,disinfection,temperature control,ammonia nitrogen and nitrite regulation.The core technology of these two kinds of circulating water aquaculture is to remove the residual feed,fish feces and other precipitation particles and suspended solids in the aquaculture water,and to create a hydrodynamic environment suitable for fish growth.The research on hydrodynamics of recirculating aquaculture system has important scientific significance and practical application value to solve the problems of low water cycle performance,poor water purification efficiency and low collection and discharge efficiency in current recirculating aquaculture system.In this paper,aiming at the key scientific problems that need to be solved urgently in circular aquaculture,combined with multiphase flow theory and CFD numerical calculation method,the hydrodynamic characteristics of a single aquaculture tank in two typical circular aquaculture systems in Shanghai agricultural demonstration projectdivided tank circular aquaculture system and typical single channel industrial circular aquaculture system were simulated and studied.The main research contents and results are as follows.(1)Based on the Euler-Euler two-fluid model,the single-phase flow numerical calculation model of a single culture tank in the tank circulating water aquaculture system was established,and the flow characteristics of the water injection process in the culture tank under different hydraulic conditions,the generation and development law of turbulence / vortex structure were mainly studied.The results show with the increase of water injection rate,the rotational angular velocity of water flow in the culture tank increases;With the increase of the rotational speed of water body,the swirling flow and swirling flow are more obvious.The closer they are to the center of the aquaculture tank,the lower their speed is.This phenomenon makes the sedimentary particles easy to gather in the middle,which is conducive to the collection and discharge of pollutants in the aquaculture tank.(2)Based on the Euler-Euler two-fluid model,the single-phase flow numerical calculation model of a single culture tank in the tank circulating water aquaculture system was established,and the flow characteristics of the water injection process in the culture tank under different hydraulic conditions,the generation and development law of turbulence or vortex structure were mainly studied.The results show with the increase of water injection rate,the rotational angular velocity of water flow in the culture tank increases;With the increase of the rotational speed of water body,the swirling flow and swirling flow are more obvious.The closer they are to the center of the aquaculture tank,the lower their speed is.This phenomenon makes the sedimentary particles easy to gather in the middle,which is conducive to the collection and discharge of pollutants in the aquaculture tank.(3)Taking a typical single-channel industrial circulating water aquaculture tank as the research object,the single-phase flow numerical calculation models of different tank structures were established.The effects of the radius of the circular arc angle on the velocity distribution,flow uniformity index,vorticity distribution and energy effective utilization coefficient of a single aquaculture tank were studied.The results show with the increase of the radius of the circular arc angle of the aquaculture tank,the turbulence intensity of the flow field in the aquaculture tank is weakened,and the flow uniformity index is on the rise.It is beneficial to reduce the generation of low-speed mixing zone in the tank and improve the mixing uniformity of the water body in the tank.The change trend of energy effective utilization coefficient and average water flow uniformity index with the fillet radius of the tank is the same,and the growth trend of the two shows a certain positive correlation.A comprehensive performance index of aquaculture tank is proposed,which can effectively evaluate the comprehensive performance of aquaculture tank and solve the problem of improving the spatial utilization rate of circular aquaculture system under the condition of ensuring good hydrodynamic conditions of circular aquaculture tank.In conclusion,the research have important scientific significance and application value to solve the problems of low water cycle performance,poor water purification efficiency and low pollution collection and discharge efficiency of circulating aquaculture system.In this paper,the relationship between the bottom structure of circular aquaculture tank and its water purification efficiency and the hydrodynamic conditions conducive to particle aggregation are obtained by numerical study.The influence factors of circular arc radius of industrialized aquaculture tank on the hydrodynamic characteristics of aquaculture tank were explored,and the comprehensive performance index for evaluating the spatial utilization rate and hydrodynamic performance of industrialized circulating water aquaculture tank was proposed.