The fluid and mechanical coupling between two circular cylinders in tandem arrangement

The effect of the fluid and mechanical coupling between two flexible circular cylinders on their vortex-induced oscillations is examined in a wind tunnel. The cylinders are in a tandem arrangement and a mechanical coupling allows vibrations in phase and out of phase. The separation between the cylinders ranges between 7 and 25 diameters. When the cylinders are coupled only by fluid, the upstream cylinder behaves as an isolated one, while the downstream cylinder response depends on the separation and presents a hysteresis and three discontinuities. The hysteresis and its discontinuities agree with those of the upstream cylinder and the third discontinuity coincides with the end of synchronization of the windward cylinder. The addition of the mechanical coupling complicates the dynamic response which is greatly influenced by the separation and the coupling mode involved. The results are interpreted according to those dealing with the fluid coupling only. The effect of small-scale grid turbulence is also examined. (C) 1999 Academic Press.