Experimental investigation on flow-induced vibration of two high mass-ratio flexible cylinders in tandem arrangement

This paper reports experimental results from flow-induced vibration (FIV) response of two identical flexible circular cylinders in the tandem arrangement. The two flexible cylinders are mounted horizontally in the test section of a subsonic wind tunnel and each cylinder has a mass-ratio of 120 and an aspect ratio of 47. The dynamic response of the system is studied for both the upstream and downstream cylinders for center-to-center separation distances in the range of 3 to 7 times the diameter of the cylinder. Amplitudes and frequencies of oscillation, as well as phase differences between the response of the upstream and downstream cylinders are studied in the reduced velocity range of U* = 4.3 - 31.7 and the Reynolds number range of Re = 2, 570 - 24, 536. The dynamic response observed in this study are presumably the result of two combined phenomena of vortex-induced vibration and wake-induced vibration. Despite the high mass-ratio of the cylinders, higher modes of vibrations, both odds and even modes, up to the fourth mode are excited in both the upstream and downstream cylinders, owing to the high -flexibility of the cylinders. While for low separation distance between the cylinders the FIV response of the upstream cylinder is under influence of the downstream cylinder, as the separation distance between the cylinders is increased, the upstream cylinder's response exhibits mono-frequency oscillations similar to those observed for an isolated cylinder. However, the FIV response of the downstream cylinder is always under influence of the upstream cylinder and as the separation distance between the cylinders is increased the response is dominated by the multi-frequency oscillations. Also, for large separation distance of 7D, as well as cases where multi-frequency oscillations occur, the synchronization between the cylinders, quantified by the phase difference between the oscillations of the cylinders, varies over the duration of oscillations. Standing -wave behavior is observed for most cases at low reduced velocity ranges for which mono-frequency oscillations dominate the response while the traveling-wave behavior is observed at higher reduced velocities at which multi-frequency oscillations dominate the FIV response of the system. (C) 2022 Elsevier Ltd. All rights reserved.