Numerical Study of Fluid Structure Interaction in Nuclear Reactor Applications

Abstract

Flow-induced vibration (FIV) plays an important role in the nuclear industry. In nuclear power plants (NPP), the FIV may cause fatigue problems, stress corrosion cracking, possible failure modes and fretting wear. This in return can lead to nuclear safety issues and substantial stand-still costs due to unplanned outages. It is therefore important to asses this phenomena early in the design process. Most of the experiments or analytical models used to predict FIV, are over simplified or cover only a single operation condition. Therefore using a combination of Computational Fluid Dynamics and Computational Solid Mechanics to model FIV can play an important role for the complex industrial applications. In the present work the numerical simulations are performed using the OpenFOAM Extend open source code, in which both the fluid and structural dynamics are computed using the Finite Volume (FV) method. Moreover, a partitioned approach was implemented, in which the exchanges between the fluid and structure solver take place. This was done through the use of the Interface Quasi Newton with Inverse Jacobian from a Least-Squares (IQN-ILS) coupling method. To gain the confidence of the available numerical methods, their validation is a necessary step that needs to be performed. Firstly the simulation of a well-known benchmark was performed using the IQN-ILS coupling method, where the deformation of an elastic flap, attached to a solid cylinder, is studied. Afterwards, the same coupling method was used to simulate the free vibration of a beam in a fluid and validated with experimental results. Lastly, the validated method was used to model the turbulence induced vibrations of a scaled version of a neutron flux measurement guide tube. From this study it has been found that the IQN-ILS coupling method can be used for strongly coupled problems. It has also been found that the mesh resolution and time step are important parameters for a correct estimation of the frequency and the damping of the oscillation.