Interference of vortex-induced vibration and galloping of a rectangular cylinder in turbulent flow

It is known that bluff bodies with sufficient afterbody may be prone to the interference of Kármán-vortex-resonance and transverse galloping in particular ranges of the mass-damping parameter (Scruton number) of the oscillating system. Such a phenomenon is not only physically interesting but also very important from the engineering standpoint, as it may imply large-amplitude oscillations in flow speed ranges where no excitation is predicted by the classical theories for vortex-induced vibration (VIV) and galloping. This work concentrates on the behavior of a spring-mounted rectangular cylinder with a side ratio of 1.5, having the short side perpendicular to the flow and free to vibrate in the transverse degree of freedom, as this geometry showed high proneness to combined VIV-galloping excitation. A wide experimental campaign was carried out in the CRIACIV wind tunnel to investigate the phenomenon in various free-stream turbulent flows. A bi-planar grid was employed to generate isotropic homogeneous turbulence with integral length scale comparable with the cross-wind section dimension of the model. In addition, eddy-current viscous dampers were used to vary the Scruton number of the system in a controllable way.