Interference effects on flow-induced oscillation of three tandem cylinders with passive turbulence control

Abstract

The characteristics of flow-induced oscillation (FIO) of cylinders in tandem change due to interference between cylinders. Identifying positive and negative interferences is vital for designing marine structures involving cylinders on elastic supports. Experiments on a single cylinder, two tandem-cylinder and three tandem-cylinder cases were conducted to study the interference due to placing an identical oscillating cylinder upstream, downstream, and both upstream and downstream. Critical parameters (damping, stiffness) and Reynolds number (Re) are varied in the tests. Both vortex-induced vibration (VIV) and galloping in these cases are identified and analyzed. The onset inflow velocity of oscillation for the cylinder is reduced and back-to-back VIV and galloping is achieved, when placing interference cylinder/s 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 due to one upstream cylinder is more vigorous than that due to 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.