Flow Behavior Behind A Freely Suspended Cylinder in the Wake of A Stationary Cylinder
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or Behind A Freely Suspended Cylinder in the Wake of A Stationary Cylinder GAO Yang-yanga, *, CHEN Wei-yia, TAN Soon Keatb, ZHANG Bao-fengc a Ocean College, Zhejiang University, Zhoushan 316021, China b Maritime Research Centre, School of Civil Environmental Engineering, Nanyang Technological University,
639798, Singapore c Powerchina Huadong Engineering Corporation Limited, Hangzhou 311122, China
Received September 12, 2019; revised August 18, 2020; accepted September 8, 2020 ©2020 Chinese Ocean Engineering Society and Springer-Verlag GmbH Germany, part of Springer Nature Abstract The experiment of flow past a freely suspended circular cylinder in the wake of an upstream stationary cylinder was carried out in a re-circulating water channel using the Particle Image Velocimetry (PIV) technique. The upstream cylinder was fixed, while the downstream cylinder was suspended from a platform and allowed to move freely in the horizontal plane. The centre-to-centre spacing ratio between two tandem cylinders was initially kept at a constant value of 3.0. The instantaneous flow field and the orbital trajectories were analyzed to reveal the effect of the presence of the upstream cylinder and flow velocity on the dynamic response of the downstream suspended cylinder. The results showed that the upstream stationary cylinder has significant effect on modifying the flow patterns behind two tandem cylinders. Different trajectories of the downstream suspended cylinder with variation of flow velocity U were observed, such as: (1) depicting a figure-8 type motion at U = 0.27 m/s; (2) undergoing intermittent oscillations as it travels downstream at 0.3 m/s ≤ U ≤ 0.37 m/s; (3) successive moving downstream, no obvious streamwise oscillation observed at U = 0.43 m/s. Key words: downstream suspended cylinder, PIV, camera, orbital response, flow pattern Citation: Gao, Y. Y., Chen, W. Y., Tan, S. K., Zhang, B. F, 2020. Flow behavior behind a freely suspended cylinder in the wake of a stationary cylinder. China Ocean Eng., 34(5): 708–717, doi: https://doi.org/10.1007/s13344-020-0064-y
1 Introduction Flow induced vibrations of circular cylinders are of interest in the area of coastal and offshore engineering, such as risers, pipelines, mooring lines etc. As well known, when the cylinder is flexible or elastically mounted, the interaction of vortex shedding with the structural characteristics of the body can lead to significant vortex induced vibration (VIV) in both the inline and cross-flow direction. This VIV phenomenon has drawn attention due to the increasing risk of fatigue failure in engineering structures. Most of the early studies on flow-induced vibration of two tandem cylinders were concerned with the flow around elastically mounted cylinders (Zdravkovich, 1985; Mahir and Rockwell, 1996; Brika and Laneville, 1999; Xu et al., 2008). Assi et al. (2006) studied flow-induced oscillations of a circular cylinder mounted on an elast
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