Abstract
Much work has been devoted to the investigation and understanding of the flow-induced vibrations of twin cylinders vibrating individually (e.g., vortex-induced vibration and wake-induced galloping), but little has been devoted to coupled twin cylinders with synchronous galloping. The primary objective of this work is to investigate the aerodynamic forcing characteristics of coupled twin cylinders in cross flow and explore their effects on synchronous galloping. Pressure measurements were performed on a stationary section model of twin cylinders with various cylinder center-to-center distances from 2.5 to 11 diameters. Pressure distributions, reduced frequencies and total aerodynamic forces of the cylinders are analyzed. The results show that the flow around twin cylinders shows two typical patterns with different spacing, and the critical spacing for the two patterns at wind incidence angles of 0° and 9° is in the range of 3.8D~4.3D and 3.5D~3.8D, respectively. For cylinder spacings below the critical value, vortex shedding of the upstream cylinder is suppressed by the downstream cylinder. In particular, at wind incidence angles of 9°, the wake flow of the upstream cylinder flows rapidly near the top edge and impacts on the inlet edge of the downstream cylinder, which causes a negative and positive pressure region, respectively. As a result, the total lift force of twin cylinders comes to a peak while the total drag force jumps to a higher value. Moreover, there is a sharp drop of total lift coefficient for α = 9–12°, indicating the potential galloping instability. Finally, numerical simulations were performed for the visualization of the two flow patterns.
Highlights
Bridge hangers in suspension bridges are commonly deployed in pairs or groups with close spacing [1], and the aerodynamic behavior of closely spaced cylinders becomes very complex and is considerably different from that of a single isolated one as a result of the interference effects
Identical, and parallel cylinders such as bundled overhead conductors, heat exchange tubers, hangers of suspension bridges, and chimney stack groups are sensitive to wake interference effects, which are associated with fatigue damage or catastrophic failure [12,13]
In the previous study by the authors [28], it is shown that the coupled twin cylinders suffered from wake-induced vibrations at certain spacings and ranges of wind attack angles
Summary
Bridge hangers in suspension bridges are commonly deployed in pairs or groups with close spacing [1], and the aerodynamic behavior of closely spaced cylinders becomes very complex and is considerably different from that of a single isolated one as a result of the interference effects. Gu et al [48] classified three different pressure distribution patterns on the downstream cylinder and observed two switching processes for the wind incidence angle varying from 0◦ (in tandem) to 90◦ (in side-by-side) at high subcritical Reynolds numbers. Effects of aerodynamic interference on the fluctuating pressures of twin circular cylinders of various wind incidence angles become weaker at the supercritical Reynolds number than those at the subcritical one [27]. In the previous study by the authors [28], it is shown that the coupled twin cylinders suffered from wake-induced vibrations at certain spacings and ranges of wind attack angles. The purpose of this work is to describe the aerodynamic forcing characteristics and flow patterns of coupled parallel twin circular cylinders through wind tunnel tests and numerical simulations.
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