Experimentally investigated vortex-induced vibration of a high aspect ratio and small mass ratio circular cylinder oscillating in low reduced velocity flows

Abstract

Experimental investigations were performed for a circular cantilevered cylinder located in a circulating water channel. The cylinder of mass ratio 1.78 and aspect ratio of 17.8 was vertically fixed at one end, and its other end was free to oscillate in the stream-wise and lateral directions. The reduced velocities of the flow past the cylinder, ranging from 0.65 to 5.18, corresponded to Reynolds numbers between 6.38 ∙ 10 3 and 5.1 ∙ 10 4 . At the inlet of the water channel, a Laser doppler velocimetry system measured stream-wise and span-wise flow velocity profiles and calculated the corresponding turbulence intensities. For differing reduced velocities, cylinder accelerations, displacements, and forces acting on the cylinder in the stream-wise and lateral directions were measured. Vortex shedding frequencies were compared with cylinder response frequencies in the stream-wise and lateral directions. Strouhal numbers were obtained at different water channel depths and widths. Coefficients of forces acting in the cylinder and trajectories of the cylinder's motions and accelerations were presented and analyzed. The main objectives were to investigate the effect of relevant parameters for a cylinder oscillating in 2-DOF, such as measuring the universal wake Strouhal number. The universal Strouhal number calculations were based on the vortex shedding frequency and then compared with published data. Directly measured shedding vortex frequencies at different locations around the cylinder and at different reduced velocities were compared with the frequencies of a stationary cylinder to obtain further insight of shedding vortex frequencies. Directly measured were cylinder accelerations, cylinder oscillations, and inertial forces acting on the cylinder and their trajectories. The maximum oscillation recorded in the lateral direction of the cylinder recorded was 0.8D, where D is the cylinder diameter, at which the lock-in phenomenon was observed, and figure eight–shaped (Lissajous) trajectory patterns were captured. The universal wake Strouhal number for different reduced velocities decreased almost linearly from 0.201 at U r = 0.6 to 0.141 at U r = 5.18. At different depths and widths, the Strouhal number was almost constant for each reduced velocity considered. Another objective was to directly measure the forces coefficients. The stream-wise force coefficients were close to the coefficients for the stationary cylinder, and, at higher Reynolds numbers, they increased. Furthermore, the uncertainty methods used here were explained in details and low uncertainties of measured values substantiated the reliability of our results. The experiments provided reliable benchmark data suitable for numerical validation of vortex-induced vibration for a circular cylinder oscillating in two degrees-of-freedom. 1 Experimental investigation of Vortex induced vibration in water circulation channel. 2 Velocity profiles and Turbulence intensities of the circulation water channel using Laser Doppler velocimetry. 3 Direct measurements of forces and dynamic response in lateral and transverse directions at different reduced velocities. 4 Shedding vortex Strouhal number measurements for oscillating cylinder in two degree of freedom. 5 Fluid-structure interaction measurements uncertainty analysis.