Vortex-induced vibrations of three rigidly coupled circular cylinders in an equilateral-triangular arrangement

Abstract

A three-cylinder system in an equilateral-triangular arrangement is a common, basic structure in the engineering field, and the rigid connection of multiple cylinders has been applied in some practical projects. In this paper, three cylinders in an equilateral triangle arrangement for a spacing ratio of 4 at Reynolds number of 200 are studied by means of numerical simulation. The vibration modes are divided into single cylinder vibration, three freely vibrating vibration and three rigidly coupled vibration. The vortex-induced vibration characteristics and aerodynamic forces and fluid–structure-interaction mechanisms are analyzed. The results show that the vibration velocity regions and the amplitude of three freely vibrating cylinders in the transverse and streamwise directions are obviously larger than that of a single cylinder. The rigid connection measures can effectively suppress the vibration velocity region and amplitude. However, this suppression effect is no better than the single cylinder. In the lock-in region, the trajectories of three rigidly coupled cylinders are regular closed shapes. The Strouhal numbers of the three cylinders are synchronous in the natural frequency in the lock-in region. The wake vortices from the upstream cylinders affect the downstream cylinders, which depends on different case and reduced velocity. The complex aerodynamic interference and parallel vortices of the wake enhance the vibration of the structure in some cases.