An experimental study of the in-line oscillations of a closely spaced row of cylinders in cross-flow

An experimental study has been carried out, to examine the vibratory motion in the streamwise direction of a closely spaced row of circular cylinders. The cylinders in the flexible row under study, free to respond in-line with the flow, are placed alternately between cylinders of a fixed row in a water channel. The transverse spacing of the cylinders of the same row was 3 cylinder diameters, yielding a cylinder spacing when the two rows were aligned equal to 1.5 diameters. The experiments were carried out at low Reynolds numbers over a range from 700 to 1200. Each programme of measurements started when the flow velocity was maximum, and the flexible row was displaced at a small distance downstream of the fixed row. As the velocity was gradually decreased and the flexible row was moved to a mean position upstream of the fixed in-line oscillations occurred, whose amplitude, which was not constant at different cycles, was dependent on both the stream velocity and the initial displacement between the two rows. For each flow velocity, the time history of the oscillation of the moving row was recorded, from which the response and the frequency of oscillations were obtained and are presented diagrammatically.