In this research numerical simulations of the flow-induced vibrations in a hexagonal tube array were compared to experimental results. Due to the presence of the tube walls, a significant velocity difference between the inter-cylinder gap and sub-channel center exists and a vortex street is generated. As this instability originates from velocity-shear, it is of the Kelvin-Helmholtz type. The fluctuating pressure associated with the vorticial flow can cause structural vibrations of the cylinders.

The computational domain was constructed such that the geometry matches an experimental setup. The central tube in the bundle of 7 tubes contains a flexible segment made of silicone, which is at both extremes clamped to the steel part of the cylinder. All other tubes are made of steel.

As first step, it was checked whether the vortex street also appears for this particular geometry, using unsteady Reynolds-averaged Navier–Stokes (URANS) simulations, with the structure considered completely rigid. As second step, the flexible segment was taken into account and coupled fluid-structure interaction (FSI) simulations were performed. Finally a comparison between the numerical and experimental results was made.