Numerical Simulation And Experiment Of CFD In Industrial Aquaculture Pond

Industrial aquaculture in ponds has outstanding advantages such as high yield,high efficiency,green and safety,and is gradually replacing traditional methods to become the mainstream model of aquaculture in China.However,as the core area of pond industrial aquaculture,two problems related to hydrodynamics have not been solved,one is that the aeration push flow effect is not good enough and seriously affects the uniformity of dissolved oxygen in water and the living environment of fish,the other is the poor settlement effect of solid particulate matter such as residual feed and fish manure at the end of the pond,which seriously reduces the collection rate of solid waste and increases the difficulty of water treatment in the back-end circulation area,there is an urgent need to study,treat and solve it.This paper taking the blowerated push pool as the research object,the response surface optimization design method is used to optimize the parameters of the aeration device and analyze the flume flow field.Based on the analysis results,on the basis of pure water,the gas phase is added to compare and verify the test data,and the oxygen content in the water is simulated and analyzed.The solid phase is added to simulate and analyze the settlement of feed particles,which provides theoretical guidance for the parameter optimization of the aeration push pond and waste collection.The main contents of this paper are as follows:(1)Three-dimensional modeling software Creo7.0 was used to model the aeration tank computational domain,and ICEM CFD was used to divide the computational domain into hexahedral grids,and the correlation of computational grids was verified.Finally,on the premise of ensuring the computational accuracy,a set of grids with less computational time were screened out.(2)For the selection of inlet velocity V,baffle plate elevation angleΦ,and aeration plate height L,which have a great influence on the performance of aeration push-flow pool,13 experimental schemes were designed by using the Box-Behnken experimental design principle in the response surface optimization design method.The response surface analysis of three factors and three levels were carried out,the influence of the interaction between factors on the flow field were analyzed,the best parameter combination with the minimum flow velocity as the optimization goal was found,and the final aeration tank structure model was determined.The actual optimization effect of the aeration tank model was scientifically and reasonably evaluated through the quantitative calculation of the velocity streamline diagram,flow velocity uniformity and velocity weighted average angle on each section of the aeration tank.(3)Based on the steady-state calculation results,the numerical calculation method of gas-liquid two-phase flow was used to simulate the free liquid surface fluctuation state of the aeration tank,gas volume fraction cloud map and distribution law of free liquid surface height along the length of the pool were extracted,the calculation results show that the height of the free liquid surface of the aeration tank from the inlet position to the outlet position is monotonically decreasing,and the relative deviation ratio of the height is 0.4%,this result indicates that the fluctuation of the liquid surface is small.At the same time,this calculation method was used to numerically calculate the aeration behavior of the pool inlet to study the distribution of air in the water,the calculation results show that the air phase flows in the tank from the entrance location of the pool and distributes on the entrails of the pool and its upper surface,the gas content on the seven characteristic sections from the pool inlet to the outlet first increases and then decreases.(4)The system of aeration push-flow test device and its velocity measurement principle were introduced in detail,140 velocity measurements and CFD calculated values from 7 different sections in the pool containing 10#California bass,15#high-density bream,and 52#channel catfish were compared and analyzed respectively,the results show that the large deviation between the experimental value of the flow velocity and the calculated value,this phenomenon is caused by the interference of fish swimming on the experimental flow field.(5)In order to obtain the sedimentation effect of different densities of fish feed particle at a fixed flow rate,particle flow simulation was carried out for three different densities of feed pellets,comparative analysis of particle settling behavior under three density conditions was carried out,velocity changes of particle swarms as they pile up in water were captured by using solid phase particle velocity nephogram,and the trajectory of a single particle was tracked randomly,the velocity changes of individual particles propelled by water flow were analyzed,calculations prove that:the feed particles with densityρ_s=1040kg/m~3could fall into the sewage collection area well under the promotion of the water flow with the inlet velocity of 8cm/s.