Study On Particle(ISPH)-Grid(FVM) Coupling Method Based On FCI In Lead Fast Reactor

The Incompressible Smoothed Particle Hydrodynamics(ISPH)method is a pure Lagrangian meshless particle method,which has significant advantages when dealing with problems such as free surfaces,two-phase moving interfaces and large deformations when comparing with traditaional grid method,but its computational efficiency is much lower than grid method.Coupling the particle method and the grid method can make full use of the advantages of the two methods.Based on the idea of region decomposition,the ISPH method is used to simulate the areas involving large deformation flows,and the FVM method is used to simulate other areas.Thus,not only the complex problems such as large deformations can be solved,but also good computing efficiency can be ensured.Finite Volume Mehod(FVM),as a Euler grid method,is currently the most widely used flow field calculation method.In this paper,the particle-grid(ISPH-FVM)coupling method is researched.Based on the Fortran language,a coupling program for the calculation of incompressible fluid flow and heat transfer is developed to provide an alternative and efficient way to simulate large deformation flow problems in the field of computational fluid dynamics.At the same time,the coupling method is used to simulate the fuel-coolant interaction(FCI)process after melting of the lead fast reactor core.Firstly,this paper discusses the basic theory of ISPH method,and derives the fluid control equation and pressure Poisson equation in ISPH form.The related numerical processing technologies involved in ISPH method are analyzed and discussed.The basic theory of FVM method and staggered grid technology are discussed,the fluid control equations in FVM form are discretized,and the pressure-velocity-coupled SIMPLE method is introduced.Based on the basic theory of ISPH and FVM,the interface processing technology of the ISPH-FVM coupling method is studied,including boundary generation technology and particle deletion and filling technology.A hybrid modified format of XSPH and CSPM is proposed for regularization of boundary particle distribution and the numerical oscillations at the coupling interface are eliminated.An iterative method to realize smooth transition of field variables on both sides of the coupling interface and a program calculation scheme of the coupling method are studied.Secondly,the coupling method is used to simulate and analyze Poiseuille flow and nonsteady plate heat conduction models.By comparing with the analytical solution,verify the correctness of the iterative process of the coupling method at the coupling interface and the effectiveness of the coupling method in the flow and heat transfer process.The shear driven cavity flow with heat transfer model is simulated.By comparing with the Fluent numerical solution,the results show that the coupling method can effectively deal with the convective heat transfer problem when there is a mass exchange on both sides of the coupling interface.The linear standing wave flow model is modeled and analyzed.By comparing with the analytical solution,the simulation of the coupled method in free surface flow problems is realized.The simulation results of the coupled method and the particle method are compared and analyzed.The results show that the coupling method has better advantages than the particle method in terms of solution accuracy and calculation efficiency.Finally,the coupling method is used to numerically simulate the process of the rigid body entering the liquid pool.By analyzing the stability and mass conservation of the coupling method,the applicability of the coupling method in dealing with complex surface flow problems such as large deformation is verified.Taking the surface tension,heat transfer phase transition and fluid-structure interaction into consideration,the coupling method is applied to the simulation study of the FCI process of lead fast reactor.The effects of different initial velocities and temperatures on the process of crushing and solidifying in the coolant for different types of molten fuel(droplet and jet)are studied.The results show that the fragmentation process of molten fuel will be affected by the combined effects of hydraulic impact crushing and thermal cooling and solidification.