Numerical Study On Flow Induced Vibration Of Reactor Rod

The cylindrical structure is impacted by internal flow or external flow,and deformations occur due to the change of surface flow force,which in turn affects the distribution of flow field.This is fluid-solid coupling.In this paper,through CFD simulation,first,the flow field around a single cylinder is simulated,and its lifting resistance characteristics and vortex shedding phenomenon downstream of the tube bundle are studied.The two-way fluid-structure coupling method is used to analyze the vibration characteristics and frequency response of a single tube at different flow rates.Then,a method combining And study the flow-induced vibration characteristics of a single rod under axial flow.The results are compared with the results in the literature to verify the feasibility of numerical simulation.Finally,established model 3D solids such as rod bundles,spacer grid,and mixing vanes,and then assembled them,and extracted the runners by shelling.The flow-induced vibration of fuel rod bundles with and without the grid and the disturbance of the vibration convection field were studied respectively.By comparing and analyzing the results of numerical simulations,the following conclusions are drawn: For the vortex-induced vibration of a single tube,in the direction of resistance,the flow direction deformation of the tube reaches a new equilibrium position after a certain time of attenuation,and finally transversely with a certain amplitude Vibration,in the direction of lift,the axial displacement of the tube increases rapidly after a certain period of time,and the single tube starts to lose stability,and the displacement response in the lift direction and the time-domain curve of the lift are consistent,which is in line with the relationship between response and displacement.When the flow velocity exceeds a certain critical value,the tube undergoes three-dimensional deformation,and Strawhar “8”-shaped vibration starts.As the flow velocity increases,the equilibrium position along the flow direction of the tube continuously moves downward.Within a certain range of flow velocity(6m/s--8m/s),the fluid excitation resonates with the tube and a "frequency lock" effect appears.By modeling 5×5 fuel rod bundles with and without grids,and simulating the flow field distribution and rod bundle vibration,it is learned that the influence of rod bundle vibration on the flow field is negligible.Therefore,this model can be simplified as a one-way fluid-structure interaction analysis.The flow-induced vibration phenomenon of the rod bundle is mainly caused by the pressure difference.The existence of the positioning grid aggravates the disturbance of the flow field,causing a larger pressure difference on both sides of the rod bundle to cause greater vibration.