Numerical study on flow-induced vibrations of elastically mounted rectangular cylinders without and with barrier walls

Abstract

This work presents a two-dimensional (2D) numerical study on the flow-induced vibrations (FIV) of elastically mounted rectangular cylinders without and with barrier walls in a wide range of reduced velocities U*=1–200 and Scruton numbers Sc=0–64 at the Reynolds number of 1000. It reveals that a slender rectangular cylinder of aspect ratio 5:1 without barrier walls may experience vortex-induced vibration (VIV), while the one with barrier walls can have both VIV and soft galloping motions. The VIV motions of both cylinders occur at relatively small reduced velocities U*≤20, and their maximum amplitudes are gradually reduced with the increase in the Scruton number. The galloping motions of the cylinder with barrier walls take place at higher reduced velocities U*>30 with smaller frequencies and larger oscillation amplitudes. Quantitative analysis on the amplitude, displacement, and frequency of oscillation for both cylinders is carried out. Two phase diagrams of the vortex-shedding flow patterns are presented to illustrate the flow characteristics in VIV and galloping modes. Meanwhile, the dynamic mode decomposition analysis indicates the difference between the dominant mode of the dynamic flow field in the VIV and galloping motions. With the quasi-steady theory, it further shows that the occurrence of the soft galloping motion of the cylinder with barrier walls is caused by the negative slope of the lift coefficient at the angle of attack zero. These results may shed new light onto deeper understanding of the FIV phenomenon and provide some inspirations to engineering applications in the design of civil and offshore structures.