We present simulation results of vortex-induced vibrations of an infinitely long flexible
cylinder at Reynolds number Re = 1000, corresponding to a ‘young’ turbulent wake
(i.e. exhibiting a small inertial subrange). The simulations are based on a new class
of spectral methods suitable for unstructured and hybrid grids. To obtain different
responses of the coupled flow–structure system we vary the structure's bending stiffness
to model the behaviour of a vibrating inflexible (rigid) cylinder, a cable, and a beam.
We have found that unlike the laminar flow previously studied, the amplitude of
the cross-flow oscillation is about one diameter for the cable and the beam, close to
experimental measurements, but is lower for the rigid cylinder. We have also found
that for the latter case the flow response corresponds to parallel shedding, but for
the beam and cable with free endpoints a mixed response consisting of oblique and
parallel shedding is obtained, caused by the modulated travelling wave motion of
the structure. This mixed shedding pattern which alternates periodically along the
span can be directly related to periodic spatial variation of the lift force. In the
case of structures with pinned endpoints a standing wave response is obtained for
the cylinder; lace-like flow structures are observed similar to the ones seen in the
laminar regime. Examination of the frequency spectra in the near wake shows that at
Re = 1000 all cases follow a −5/3 law in the inertial range, which
extends about half a decade in wavenumber. However, these spectra are
different in all three cases both
in low and high frequencies, with the exception of the beam and cable, for which the
high-frequency portion is identical despite the differences in the displacement time
history and the large-scale features of the corresponding flow.