Drag Coefficients of a Long Flexible Circular Cylinder With Wake Interference

Drag coefficients of the downstream cylinder in a tandem arrangement of two models aligned with the flow are shown in this work. The models, which experienced vortex-induced vibrations with wake interference, had an external diameter of 16 mm and a total length of 1.5 m giving an aspect ratio of about 94. More than 400 runs were carried out in a water flume with only the lower 40% of the models exposed to the current. The flow speed was varied up to 0.75 m/s giving Reynolds numbers in the range from 1200 to 12000. A supporting structure, where the models were attached, allowed changes in the centre to centre distances and in the applied top tensions. Separations of up to 4 diameters were tested with tension variations from 15 to 110 N. Reduced velocities based on the fundamental natural frequency reached values up to 16. The mass ratio of the models was around 1.8 and the combined mass-damping parameter about 0.05.