Vortex-induced vibration response of a cactus-inspired cylinder near a stationary wall

Abstract

Vortex-induced vibration (VIV) responses of a cactus-inspired cylinder near a stationary wall are numerically studied, and the effects of the height ratios (Ks/D, Ks is the height) of the cactus-inspired structure and the stationary wall on VIV response are discussed in detail. The VIV response region is usually divided into four sub-regions, namely, the initial branch (region I), the upper branch (region II), the lower branch (region III), and the desynchronization branch (region IV). The Reynolds number at which the maximum vibration amplitude occurs for the cylinder near the stationary wall is lower than that of a free-standing cylinder. The Reynolds number at which the maximum amplitude occurs decreases with an increase in the height ratio of the structure. Due to effects of the stationary wall, the critical reduced velocity at which the vortex phase jump occurs decreases. With an increase in the height ratio of the structure, the critical reduced velocity at which the vortex phase jump occurs gradually decreases. Vortex shedding is seen from the stationary wall, and the vortex moves clockwise. This vortex can weaken vortex shedding from the cylinder. Due to the large-amplitude motion, the vortex shedding from the cylinder is coupled with the stationary wall, which promotes the separation of the wall boundary layer. With an increase in the height ratio of the structure, the absolute value of vortex intensity gradually decreases, and the distance between the vortex-shedding position and the cylinder gradually increases. Therefore, the cactus-inspired structure not only changes the form of the wake vortex, but also changes the strength of the wake vortex.