Numerical And Experimental Studies On Hydrodynamic And Turbulence Characteristics Of Net Panels

The net is the main component of the cage,and its main function is to delineate the range of fish activities,ensure the exchange of water,and provide a reliable growth habitat.It is of great significance to clarify that the hydrodynamic and turbulent characteristics of the net are related to the fishability of aquaculture and the safety of cage design.The net is small-scale porous structure.Existing research often simplifies the flow field as isotropic,and uses the net lines as cylinders to study the hydrodynamic and turbulent characteristics.However,due to this physical approximation and geometric equivalence,the obtained results often deviate greatly from the actual ones.In view of this,this paper takes the net panels as the object,and conducts research on the actual three-strand spiral net lines structure.Based on numerical and experimental methods,this paper studies the effects of simplified methods(cylinder equivalent and twist equivalent),net sizes(the whole net and net unit),and turbulence models(two equation model and Reynolds stress model)on the hydrodynamic and turbulence characteristics for net panels.This paper evaluates a turbulent model for flow and analyzes the advantages and disadvantages of the two-equation model and the Reynolds stress model.It is found that the accuracy of the Reynolds stress model and the two-equation model is not much different in predicting the resistance of the net,but the Reynolds stress model can better capture the details of the flow field,accurately reflect the velocity change of the flow field,and more accurately predict the distribution of the flow field.This paper discusses the size of nets and analyzes the differences in the distribution of resistance and flow fields between net unit and overall net.It is concluded that the resistance coefficient of different sizes of nets varies with the Reynolds number,and the overall net resistance is not simply equivalent to the superposition of the net unit resistance.It is clear that the resistance of the net is not only related to the flow velocity,but also affected by the density,material,mesh size and other net parameters.This paper compares the simplification strategies of nets.It is clarified that the twist equivalent increases the drag coefficient compared to the cylinder equivalent.And the twist equivalent will inhibit the vortex,aggravating the breakage of the vortex,resulting in the reduction of the turbulent kinetic energy,changing the velocity distribution of the flow field and the Reynolds stress distribution,and affecting the flow field characteristics.