FSI-analysis on vibrations of a slender rod exposed to axial flow. Calculations for nuclear power applications.

Abstract

Vibration on components caused by flow, so called flow induced vibrations (FIV), is an important area in many industrial fields. Fluid-structure interaction problems can be solved by coupling a structure solver to a fluid solver and in each time step iterate to a solution. Different solvers can be used, but the coupling codes still need to be tested and evaluated to be used for industrial purposes. Experiments have been performed to create data for FSI-software validation and to see how an axial flow along a slender structure can cause vibrations of the structure. In order to prove the reliability of the FSI-simulation software the purpose of this master’s thesis is to see if the rod vibrations, induced by the axial flow, can be predicted with coupled FSI-simulations in ANSYS. An FSI-analysis of the same geometry as in the experiments has been carried out and the simulation data were compared to the experiment data. Different meshes, different turbulence models and structural damping were also investigated on how they affected the solution. The LES turbulence model could induce vibrations, while the URANS turbulence model could not. The vibration frequencies match the eigenfrequencies for the tube. The amplitudes increase with increased mass flow. The amplitudes were far too high and the frequencies were a bit higher in the simulations compared to the experiment. The differences could be because of discrepancies between the ANSYS model and the experiment, since there were some uncertainties in the documentation of the experiment. The simulations seemed not to be sensitive to time step or damping, but a coarse mesh resulted in lower amplitudes compared to a finer one.