Wake interference between two circular cylinders

This paper deals with an experimental investigation of the vortex-induced oscillations of a long flexible circular cylinder immersed in the wake of an identical cylinder. In comparison with the hysteretic response of an isolated cylinder, the steady-state response of the cylinder downstream of a stationary one is represented by a single branch and shows a wider synchronization region that decreases with increasing values of the spacing between the cylinders. When the upstream cylinder is free to oscillate, the downstream cylinder response becomes hysteretic. The hysteresis is characterized with two branches and two discontinuities; each branch is associated with a particular vortex pattern and the discontinuities coincide with those of the upstream cylinder. The results also indicate that beyond an inclination beta = 20 degrees of the bundle, the leeward cylinder behaves as an isolated one.