Cross-flow oscillations of a circular cylinder with mechanically coupled rotation

TL;DR

This study investigates how mechanically coupled rotation influences flow-induced vibrations of a circular cylinder, revealing enhanced oscillation amplitudes and wider lock-in regions, with implications for energy harvesting devices.

Contribution

It introduces a novel coupled rotation mechanism in FIV analysis, demonstrating its effects on wake synchronization and oscillation growth, expanding understanding of fluid-structure interactions.

Findings

Magnified oscillation amplitudes in lock-in due to coupling

Widened lock-in velocity domain with coupled rotation

Phase alignment sustains indefinite amplitude growth

Abstract

Flow-Induced Vibrations (FIV) of an elastically mounted circular cylinder are investigated by means of two-dimensional simulations. A mechanical coupling between cross-flow translation and rotation provides a single degree-of-freedom system in which the coupled rotational oscillations affect the fluid-structure dynamics. The structural response of this system is investigated exploring the design space spanned by reduced velocity, coupling radius, and phase density ratio. The kinematic coupling introduces the rotation-induced shear layer modifications, as well as an equivalent inertia effect connected to the coupling force. Such a computational campaign is carried out by means of direct numerical simulations with immersed boundary forcing at a Reynolds number equal to 100. The investigated system exhibits the wake-body synchronisation features typical of lock-in for non-rotating cylinders. However, the kinematic coupling provides a novel FIV scenario, in which the oscillation amplitude is magnified in the locked configurations with respect to the forced rotation case. Furthermore, it is found a significant widening of the reduced velocity domain where the lock-in condition takes place. In view of the proposed analyses, it is determined that the coupled rotation guarantees the phase alignment between lift and displacement necessary to sustain the lock-in condition, making the oscillation amplitude grow indefinitely with the reduced velocity. This is inherently achieved due to the rotational shear layer and the added mass contribution, which prevent the exact match between oscillation frequency and system natural frequency in vacuum. The outcomes of this study might potentially lead to innovative water energy harvesters offering larger power outputs and extended optimal operating regions.