LAUSR

Abstract Flow-induced vibration (FIV) of an elastically mounted circular cylinder with four different mass-damping parameters m ∗ ζ ( = 0.184, 0.288, 0.407, 0.719) placed in the wake of a fixed one has been studied in a wind channel at Reynolds number Re = 4000–48000. The spacing ratios S/D are from 1.1 to 8.0 (where S is the center-to-center spacing and D is the cylinder diameter). Two initial conditions, ‘from rest’ and ‘increasing velocity’, are used in the test. The vibration amplitude responses, oscillation frequency and vortex shedding frequency are analyzed and discussed. Based on the m ∗ ζ , S/D and initial conditions, results indicate that, for both ‘from rest’ and ‘increasing velocity’ cases, the downstream cylinder exhibits three regimes of vibration responses: pure VR (vortex resonance), separated VR and wake-induced galloping (WIG), and combined VR and WIG. However, the S/D for the occurrence of each regime will be changed depending on m ∗ ζ and initial conditions. Vortex resonance, gap flow and the unsteady vortex-structure interactions can contribute to the vibrations. When the spacing is small, an obvious hysteresis phenomenon can be observed for ‘from rest’ and ‘increasing velocity’. As S/D increases, the hysteresis can be negligible and the vibration characteristics are nearly the same for various initial conditions. By comparing with the results between high m ∗ ζ performed in wind tunnel at present and low m ∗ ζ in water tunnel, it can be found that, with the increasing of m ∗ ζ , the vibration amplitude and region are gradually decreasing. And the vibration regime, oscillation frequency and vortex shedding frequency are significantly different.