  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.
