Effects of Reynolds number and surface modification on wake-induced vibrations of two staggered circular cylinders

This study explores the role of Reynolds numbers (Re) in wake-induced vibrations (WIVs) of two cylinders, specifically wake galloping and two-degree-of-freedom coupled flutter on the downstream cylinder. The centerto-center distances between the cylinders were 3.0D - 5.0D in along-flow direction and 0.0D - 2.0D in cross-flow direction (D is the diameter of the cylinders). The Re ranged from 1.4 x 104-6.7 x 104, within the subcritical Re regime of a smooth cylinder. The supercritical Re regime was realized by winding 12 spiral protuberances along the cylinders to lower the critical Re. Descriptions of wake interference of two smooth cylinders at Re = 850-6.5 x 105 were summarized from the literature. Wake interference strongly depended on Re, even within the subcritical Re regime. WIVs mostly occurred in the upper subcritical Re regime with strong wake interference. In the supercritical Re regime, the wakes of the cylinders were narrowed and vortex shedding was suppressed. Consequently, the wake interference and WIVs were weakened or completely disappeared. The cylinders fitted with 12 spiral protuberances reportedly reached the supercritical Re regime at Re = 3.1 x 104. Resultantly, they were stable against WIVs above this Re even at close spacing, and suitable for stay cable applications.