Numerical Analysis Of The Turbulent Flow In Sub-channels With Square Lattice

With the development of computer technology and Computational Fluid Dynamics,the application of Computational Fluid Dynamics on thermal hydraulic analysis has been widely used in nuclear engineering.Due to the computer capability's limitation,the calculating domain is chosen in the typical part,so the boundary condition should be defined.The interaction between the adjacent sub-channels is put forward.At present,different boundary conditions are chosen in papers about the numerical analysis of the cooling fluid flow in sub-channels.In some papers,symmetry boundary condition was chosen to cut out the interaction between the adjacent sub-channels,so the problems were simplified.However,some researchers used period boundary condition to deal with the interaction.But none of the boundary conditions is verified,which is a problem for the research CFD used.Therefore in this paper,the turbulent flow in the core was simulated with CFD to analyze the boundary conditions and the interaction between the adjacent sub-channels.In this paper,a model of two adjacent sub-channels was built.Numerical calculation was made with the periodic and symmetry boundary conditions to analyze the flow fields respectively.The influences of p/d and Re on the turbulent flow between the adjacent sub-channels were studied.The steady calculating results show that both the periodic and symmetry boundary conditions are reasonable for the steady conditions,while the transient results are not.The boundary condition for transient condition is suggested according to Re and especially p/d.Simulation results in different conditions with p/d in the range of 1.05-1.3 were analyzed.When p/d is greater than 1.15,both of the boundary conditions can be chosen.When p/d is not greater than 1.15,the flow mixing between adjacent sub-channels makes periodic boundary conditions reasonable.The numerical results of flow mixing between adjacent sub-channels shows that p/d=1.15 is the boundary for the mixing.When p/d is not greater than 1.15,the flow mixing between two sub-channels arises at the moment that the flow becomes turbulence.The intensive mixing flow has a great effect on the distribution of the flow field.When p/d is greater than 1.15,the flow mixing is week.The weak mixing between sub-channels have a minimal influence,which can be left out.So p/d=1.15 can be the dividing line for tight lattice.The p/d has more significant influence than Re.When Re is a constant,the amplitude and frequency of fluctuant mixing velocity will decrease with p/d increasing,until the mixing disappears.When p/d is not greater than 1.15,the mixing between the adjacent sub-channels always exists The frequency increases by the increase of Re.When p/d is greater than 1.15,the flow mixing is too week.The minimal influent of the amplitude on flow field can be left out.Then the frequency increases as Re rises.