Development And Validation Of Solver Based On Immersed Boundary Method

Sodium-cooled fast reactor(SFR)that is one of the important types of the fourth-generation reactors has adopted passive shutdown assembly to ensure system safety.However,due to the existence of complex geometries,hole structures and moving boundaries,traditional CFD codes using body-fitted grids often encounter problems when dealing with the process of simulating the shutdown process of the passive shutdown assembly,even with unstructured grids.Therefore,it is necessary to develop powerful and versatile numerical simulation tools and adopt accurate and effective numerical methods to simulate these actual complex engineering conditions.This work develops a corresponding solution program based on the immersed boundary method,which does not need to construct a complex body-fitted grid and uses a simple Cartesian grid.The boundary conditions are represented by the addition of an ad-hoc body force in the momentum equations.The effect of classical no-slip boundary conditions at the physical surface of the immersed body is represented by the body force.Furthermore,various 2D well-documented test cases of academic flows around fixed or moving cylinder have been simulated and carefully validated with existing data from the literature.Simulation results include vortex characteristic parameters,drag coefficients,lift coefficients,Strouhal number,and vortex shedding constitutions.The results compared with literature showed this code has good efficiency and accuracy.For high Reynolds number flow,the RANS-k Epsilon model is used to solve.And sampling points are introduced for each immersed boundary node to obtain the yplus.The tangential velocity at the near wall and the wall shear stress are calculated by the wall function based on yplus of sampling poingts.The axial flow of the cylinder is characterized by changing the dimensionless parameter Reynolds number based on radius(0)₍₆₎and the ratio of the cylinder height to the radius(/(6),where the range of0)₍(6) is 2600?92310 and the range of/(6 is 3.77?850.Different turbulent conditions are simulated with the change of those two parameters,and comparing the friction coefficient with DNS and experimental results.The results show that the solver of this paper to calculate the three-dimensional turbulent conditions of cylindrical axial flow has good accuracy.Based on the above validation,the hydraulic suspended passive shutdown system are modeled,and the passive rod part is initially simulated to obtain the velocity distribution.The purpose of this paper is to develop a CFD solver that can be used to simulate the process of falling down of passive shutdown system.The simulation results have some practical significance for the future work.