On the wake-induced vibration of tandem circular cylinders: the vortex interaction excitation mechanism

TLDR

WIV shows a sustained amplitude increase at high reduced velocities, unlike VIV which is limited to a resonance range. The study investigates the mechanism of wake‑induced vibrations in tandem circular cylinders through experiments. WIV of the downstream cylinder arises from unsteady vortex–structure interactions with the upstream wake, where coherent vortices generate unsynchronized fluid force fluctuations and a favorable phase lag between displacement and force enables positive energy transfer, sustaining oscillations; eliminating these vortices suppresses WIV. Experiments in steady shear flow revealed that the fluid forces on the downstream cylinder originate from the upstream wake interactions.

Abstract

The mechanism of wake-induced vibrations (WIV) of a pair of cylinders in a tandem arrangement is investigated by experiments. A typical WIV response is characterized by a build-up of amplitude persisting to high reduced velocities; this is different from a typical vortex-induced vibration (VIV) response, which occurs in a limited resonance range. We suggest that WIV of the downstream cylinder is excited by the unsteady vortex–structure interactions between the body and the upstream wake. Coherent vortices interfering with the downstream cylinder induce fluctuations in the fluid force that are not synchronized with the motion. A favourable phase lag between the displacement and the fluid force guarantees that a positive energy transfer from the flow to the structure sustains the oscillations. If the unsteady vortices are removed from the wake of the upstream body then WIV will not be excited. An experiment performed in a steady shear flow turned out to be central to the understanding of the origin of the fluid forces acting on the downstream cylinder.