Frequency capture phenomenon in tandem cylinders with different diameters undergoing flow-induced vibration

Abstract

A frequency capture phenomenon in which the dominant response frequency of the downstream cylinder is the same as that of the upstream cylinder despite the differences in their physical characteristics was recently experimentally identified. The mechanism of this phenomenon is investigated by flow around two cylinders with unequal diameters undergoing flow-induced vibrations (FIV) using the open-source code OpenFOAM. Two FIV systems, a large stationary/vibrating upstream cylinder and vibrating downstream cylinder, are used for the simulation. The cylinders are free to vibrate in both the in-line and cross-flow directions. The forgetting factor least squares algorithm is applied for the time-varying excitation mechanism analysis. Simulation results show that the response of the downstream cylinder has a larger amplitude and contains multi-frequency components than the vortex-induced vibration of an isolated cylinder, making its trajectory more complicated. Simulations confirm that the frequency capture phenomenon is induced by the action of the upstream shedding vortex on the downstream cylinder. The energy transfers from vorticity to the structure when the frequency capture phenomenon occurs. The response of the downstream cylinder comprises a significant component of the vortex shedding frequency of the upstream cylinder.