Flow-mediated interaction between a forced-oscillating cylinder and an elastically mounted cylinder in less regular regimes

This study investigates the interaction between an actively oscillating cylinder and a passive cylinder elastically mounted with a damper. Both cylinders are rigid, immersed in a viscous fluid, of the same diameter and constrained to move along the two cylinders’ centerline. This problem is simulated by an in-house finite-element solver. Six non-dimensional groups are chosen as input: the active cylinder’s frequency f1/fn = 0.05 – 3.2 and amplitude A1/D = 0.159 – 1.432, the passive cylinder’s damping ratio ζ = 0, 0.02 and mass ratio m* = 2, the Reynolds number Rem = 35 - 315, and gap distance G/D = 2.5. The resulting Keulegan–Carpenter and the Stokes numbers are KC = 1 - 9 and b = 35. In total, 2176 combinations are studied in this parametric space. An increase in KC leads to higher irregularity and larger vibration amplitude of the passive cylinder. In regime C, the passive cylinder vibrates in a pulse-beating pattern due to the periodic switching of the streaming direction. In regime E, the passive cylinder responds with intermittent irregularity. In regime F, the flow structure switches intermittently among unrecognizable irregularities and three regular patterns resembling those observed in regimes C and E. In regime G, the flow is highly irregular and circular, where vortices shed from consecutive cycles can merge, forming a much larger one.