Turbulent intensity effect on axial-flow-induced cylinder vibration in the presence of a neighboring cylinder

Abstract

Experimentally investigation is conducted on the turbulent intensity effect on the axial-flow-induced vibration of an elastic cylinder in the presence of a neighboring rigid cylinder. The center-to-center cylinder spacing P∗ (= P/D, where D is the cylinder diameter) is 1.21, 1.36, 1.57 and ∞ (an isolated cylinder). The dimensionless velocity U¯ (=U∞L(mf∕EI)1∕2, where U∞, L, mf, EI, are the free-stream velocity, cylinder length, added mass of fluid per unit length and cylinder flexural rigidity, respectively) is 0.64 ∼ 6.92, and two ranges of incident turbulent intensity Tu are 0.71%–0.80% and 2.30%–2.91%. The cylinder vibration and the flow are simultaneously captured using two laser Doppler vibrometers and a time-resolved particle image velocimetry, respectively. It is found that the level of Tu may have a pronounced effect on the vibration of the elastic cylinder. At high Tu (2.30–2.91%), the vibration amplitude of the elastic cylinder is significantly increased compared with its counterpart at low Tu (0.71–0.80%). Two factors are found to be responsible. Firstly, the instability of the shear layer around the elastic cylinder is amplified through the interaction between the incident flow fluctuation of the high Tu and the unstable shear layer around the vibrating cylinder. As a result, eddies are prone to separation from the cylinder wall, increasing the cylinder-wall pressure fluctuations. Secondly, the eddies are observed to bounce out and then bounce back, thus enhancing unsteady fluid forces.