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Wind and Structures
  Volume 26, Number 2, February 2018, pages 57-68
DOI: http://dx.doi.org/10.12989/was.2018.26.2.057
 


Experimental study on wake-induced vibrations of two circular cylinders with two degrees of freedom
Xiaoqing Du, Benjian Jiang, Chin Dai, Guoyan Wang and Suren Chen

 
Abstract
    Wind tunnel tests are conducted to investigate wake-induced vibrations of two circular cylinders with a center-to-center spacing of 4 diameters and attack angle varying from 0 to 20 for Reynolds numbers between 18,000 and 168,800. Effects of structural damping, Reynolds number, attack angle and reduced velocity on dynamic responses are examined. Results show that wake-induced vortex vibrations of the downstream cylinder occur in a wider range of the reduced velocity and have higher amplitudes in comparison to the vortex-induced vibration of a single circular cylinder. Two types of wake-induced instability phenomena with distinct dynamic characteristics are observed, which may be due to different generation mechanisms. For small attack angles like 5 and 10, the instability of the downstream cylinder characterizes a one-degree-of-freedom (1-DOF) oscillation moving in the across-wind direction. For a large attack angle like 20, the instability characterizes a two-degree-of-freedom (2-DOF) oscillation with elliptical trajectories. For an attack angle of 15, the instability can transform from the 1-DOF pattern to the 2-DOF one with the increase of the Reynolds number. Furthermore, the two instabilities show different sensitivity to the structural damping. The 1-DOF instability can be either completely suppressed or reduced to an unsteady oscillation, while the 2-DOF one is relatively less sensitive to the damping level. Reynolds number has important effects on the wake-induced instabilities.
 
Key Words
    two circular cylinders; wind tunnel test; wake-induced vibration; Reynolds number effect
 
Address
Xiaoqing Du and Benjian Jiang: Department of Civil Engineering, Shanghai University, Shanghai, China
Chin Dai: Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai, China
Guoyan Wang: School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai, China
Suren Chen: Department of Civil and Environmental Engineering, Colorado State University, Colorado, United States
 

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