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

Flow-induced vibration (FIV) of two tandem flexible circular cylinders is studied, experimentally. Two identical cylinders with an aspect ratio of 47 and a mass ratio of 120 were held fixed at both ends and placed horizontally in the test-section of a subsonic wind tunnel. The downstream trailing cylinder lied in the wake of the upstream one and the dynamic response of the cylinders are studied for center-to-center spacing range from 3 to 7 times the cylinder diameter. Amplitudes and frequencies of oscillation are studied in the reduced velocity range of U*=3.6-63 and the Reynolds number range of Re = 187-1530. In previous studies on FIV of tandem flexible cylinders, either higher modes of the vibration than the first were not excited in the flow ranges tested or the cylinders had asymmetric boundary conditions at two ends. In the current wind tunnel experiments on FIV of two tandem flexible cylinders despite the high mass ratio of the cylinders, higher modes of vibrations up to the 4^th mode in the crossflow direction are excited owing to the high-flexibility of the cylinders. In addition, the cylinders are fully submerged in uniform flow and the boundary conditions are carefully controlled to be symmetric.