Flow characteristics around a circular cylinder subjected to vortex-induced vibration near a plane boundary Shih-Chun Hsieh a , Ying Min Low b,n , Yee-Meng Chiew a a School of Civil and Environmental Engineering, Nanyang Technological University, Singapore b Centre for Offshore Research and Engineering, Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore article info Article history: Received 16 November 2015 Received in revised form 15 April 2016 Accepted 11 June 2016 Keywords: Vortex-induced vibration Particle image velocimetry Wake Turbulence abstract Although vortex-induced vibration (VIV) has been extensively studied, much of existing literature deals with uniform flow in the absence of a boundary. The VIV flow field of a structure close to a boundary generally remains unexplored, but it can have important engineering implications, such as pipeline scour if the boundary is an erodible seabed. In this paper, laboratory experiments are performed to investigate the flow characteristics of an elastically mounted circular cylinder undergoing VIV, and a rigid plane boundary is considered to simplify the problem. The initial gap-to-diameter ratio is fixed at 0.8, and six different reduced velocities are considered. The velocity field is measured using a high resolution particle image velocimetry (PIV) system, which has several advantages over traditional PIV systems, including high sampling rate and the ability to mitigate scatter of laser light near the boundary, allowing accurate measurements at the viscous sublayer. This paper presents the vibration amplitude and oscillation frequency for different V r ; in addition, the mean velocity field, turbulence characteristics, vortex behavior, gap flow velocity, and normal/shear stresses on the boundary were measured/calculated, leading to new insights on the flow field behavior. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Fluid-structure interactions, which occur in many fields of engineering, have been studied extensively. A prominent class of fluid-structure interaction is vortex-induced vibration (VIV), which has important implications in a variety of engineering applications including heat exchanger tubes, offshore structures, electrical transmission lines, and cable-stayed bridges. VIV is essentially a nonlinear phenomenon, in which the vibration of the structure is induced by vortex shedding, while the vibrating structure in turns affects the flow field and the resulting fluid forces acting on the structure. Many research studies in VIV focus on the amplitude response of a circular cylinder attached to a spring, for example Sarpkaya (1979); Bearman (1984); Sumer and Fredsøe (1997); Khalak and Williamson (1999). A combined parameter, namely the mass-damping ratio m * ζ, has been commonly used to characterize the maximum amplitude response A * . Herein, m * ¼ mass ratio, which is the structural mass divided by displaced fluid mass, ζ ¼ damping ratio, A * ¼ A/D, A ¼ vibration amplitude, and D ¼ cylinder diameter. For the low m * ζ case, the variation of A * with the reduced velocity V r (where V r ¼ u 0 /f N D, u 0 ¼ free stream velocity, f N ¼ natural frequency in fluid) can be classified into three distinct branches, specifically the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jfs Journal of Fluids and Structures http://dx.doi.org/10.1016/j.jfluidstructs.2016.06.007 0889-9746/& 2016 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: ceelowym@nus.edu.sg (Y.M. Low). Journal of Fluids and Structures 65 (2016) 257–277