Experimental Investigation of Flow-Induced Vibrations Interference Between Two Circular Cylinders in Tandem Arrangements

This paper presents experimental results concerning flow-induced oscillations of rigid-circular cylinders in tandem. Preliminary results are presented: new measurements on the dynamic response oscillations of an isolated cylinder and flow interference of two cylinders in tandem are shown. The oscillations are due to vortex-induced vibrations (VIV). Models are mounted on an elastic base fitted with flexor blades and instrumented with strain gages. The base is fixed on the test section of a water channel facility. The flexor blades possess a low damping characteristic [ζ ≈ 0.008 and less] and they are free to oscillate only in the cross-flow direction. The Reynolds number of the experiments is from 3,000 to 13,000 and reduced velocities, based on natural frequency in still water, range up to 12. The interference phenomenon on flow-induced vibrations can be investigated by conducting experiments in two ways: first, the upstream cylinder is maintained fixed and the downstream one is mounted on the elastic base; subsequently, an investigation will be carried out letting both cylinders oscillate transversally. The results for an isolated cylinder are in accordance with other measurements in the literature for m* ≈ 2 and m* ≈ 8. For the tandem arrangement (m* ≈ 2), the trailing cylinder oscillation presents what previous researchers have termed interference galloping behaviour for a centre-to-centre gap spacing ranging from 3·0D to 5·6D. These initial results validate the experimental set up and lead the way for future work; including tandem, staggered and side-by-side arrangements with the two cylinders free to move.