Vortex-induced vibrations and lock-in phenomenon of bellows structure subjected to fluid flow

This paper deals with an experimental study on vortex-induced vibrations of bellows structures subjected to fluid flow. In the experiments, the bellows structure consists of flexible convolutions, and is subjected to fluid flow in a water channel. The vibration strains of the flexible convolutions are measured with increasing flow velocity. The vortex-induced responses are examined with changing the convolution pitch and number of the flexible convolutions. Moreover, the vortex shedding coupled with the vibrations of the convolutions is visualized. As a result, it is clarified that the vortex-induced vibration and lock-in phenomenon occur to the flexible bellows structures with large amplitude. The boundary of the lock-in region and Strouhal number are clarified, and detailed excitation mechanism of the vortex-induced vibration and lock-in phenomenon due to the vortex shedding is presented.