The fluid and mechanical coupling between two circular cylinders in tandemarrangement

The effect of the fluid and mechanical coupling between two flexible circul ar cylinders on their vortex-induced oscillations is examined in a wind tun nel. The cylinders are in a tandem arrangement and a mechanical coupling al lows vibrations in phase and out of phase. The separation between the cylin ders ranges between 7 and 25 diameters. When the cylinders are coupled only by fluid, the upstream cylinder behaves as an isolated one, while the down stream cylinder response depends on the separation and presents a hysteresi s and three discontinuities. The hysteresis and its discontinuities agree w ith those of the upstream cylinder and the third discontinuity coincides wi th the end of synchronization of the windward cylinder. The addition of the mechanical coupling complicates the dynamic response which is greatly infl uenced by the separation and the coupling mode involved. The results are in terpreted according to those dealing with the fluid coupling only. The effe ct of small-scale grid turbulence is also examined. (C) 1999 Academic Press .