Numerical Investigation on Vortex-Induced Vibrations of Two Cylinders with Unequal Diameters

Abstract

A series of numerical simulations of two-degree-of-freedom vortex-induced vibration of two coupled cylinders with unequal diameters are performed at the Reynolds number of 20,000. The effects of incident angle, spacing ratio, and diameter ratio on the VIV responses for two cylinders are investigated. It is shown that the lock-in range of the large cylinder is significantly widened and the maximum vibration amplitude decreases as a result of the existence of small cylinder. The mean drag coefficients and root mean square force coefficients of the large cylinder are not varied significantly with the incident angle and diameter ratio, but the force coefficients of the small cylinder vary considerably under different configurations. For the configuration of α = 0°, d/D = 0.05 and G/D = 0.05, the variations in vibration amplitude and frequency ratio are similar to those of the isolated cylinder. Different vortex shedding modes such as 2S mode, P+S mode, and 2P mode are observed for two coupled cylinders at different reduced velocities for different configurations.