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

Abstract

This paper deals with an experimental study of vortex-induced vibrations of bellows structure subjected to fluid flow. The characteristics of the vortex-induced vibrations and Strouhal number Stp are examined experimentally with changing the pitch length and number of flexible convolutions. The fluid flow around the vibrating convolutions is visualized and the structure of the vortex street is clarified. As a result, it is found that the lock-in phenomenon occurs to the bellows structure in out-of-phase mode due to the coupling between the vibration of the convolutions and vortex street generated along the convolutions. Strouhal number Stp based on the convolution width is about 0.18, and is independent of pitch ratio p/D in the range of p/D = 2.0-4.0.