Interference Effects on Flow-Induced Oscillation of Three Tandem Cylinders With Passive Turbulence Control

Abstract

The characteristics of flow-induced oscillation (FIO) of multiple tandem cylinders with passive turbulence control (PTC) change due to interference between PTC cylinders. Identifying positive and negative interferences is vital for designing marine structures involving PTC cylinders on elastic supports. Experiments on a single PTC cylinder, two PTC cylinders and three PTC cylinders in tandem were conducted to study the interferences due to placing an identical oscillating PTC cylinder upstream, downstream, and both upstream and downstream. Critical parameters (damping, stiffness) and Reynolds number (Re) are varied in the tests. The onset inflow velocity of oscillation is reduced and back-to-back vortex-induced vibration (VIV) and galloping is achieved, when placing interference cylinders in the vicinity of the basic oscillator. The interference due to the downstream cylinder enhances FIO of the basic oscillator. In the VIV region, one interference downstream cylinder is more effective than two interference downstream cylinders. In the galloping region, the enhancement improves for two interference cylinders for lower stiffness and damping ratios. The interference upstream cylinder tends to suppress FIO of the basic oscillator for higher stiffness. The suppression of one upstream cylinder is more vigorous than that of two upstream cylinders in the VIV region, and the opposite is true in the galloping region. When two interference cylinders are placed both downstream and upstream of the basic oscillator, its FIO is enhanced for the lower stiffness whilst it is suppressed for the higher stiffness.