Flow-Induced Vibrations of Bellows Structures Coupled With Vortex Street

This paper deals with an experimental study on flow-induced vibrations of a two-dimensional flexible bellows structure subjected to fluid flow. Experiments are conducted to clarify the detailed characteristics of the flow-induced vibrations of periodic flexible convolutions coupled with vortexes generated in shear layer of the fluid flow. In the experiments, a test section consists of flexible convolutions supported by plate springs is set in a water channel and is subjected to water flow. The vibrations of the flexible convolution are measured with increasing flow velocity. The flow-induced responses are examined with changing the convolution pitch, number of the flexible convolutions and structural damping. Moreover, the dynamic behavior of the flow pattern coupled with the vibrating convolutions is visualized. As a result, it is found that flow-induced vibrations, with large amplitude and lock-in phenomenon, occur to the flexible convolutions. Two types of vibration modes with periodic large vortex street generated in the shear layer over the cavity between the convolutions are observed. It is clarified that the two types of periodic vortex streets are moving downstream synchronized with the flexible convolution vibrations. The vibration region (stability map) and the Strouhal number are clarified. Moreover, the excitation mechanism of the flow-induced vibration coupled with vortexes is discussed based on the flow patterns.