Abstract
Abstract. Vortex-induced vibrations (VIVs) of wind turbine towers can be critical during the installation phase, when the rotor–nacelle assembly is not yet mounted on the tower. The present work uses numerical simulations to study VIVs of a two-dimensional cylinder in the transverse direction under flow conditions that are representative of wind turbine towers both from a fluid dynamics and structural dynamics perspective. First, the numerical tools and fluid–structure interaction algorithm are validated by considering a cylinder vibrating freely in a laminar flow. In that case, both the motion amplitude and frequency are shown to agree well with previous results from the literature. Second, VIVs are modelled in the turbulent supercritical regime using unsteady Reynolds-averaged Navier–Stokes equations. In this context, the turbulence model is first validated against flow past a stationary cylinder with a high Reynolds number. Then, the results from forced vibrations are validated against experimental results for a range of reduced frequencies and velocities. It is shown that the behaviour of the aerodynamic damping changes with the frequency ratio and can therefore lead to either self-limiting or self-exciting VIVs when the cylinder is left to freely vibrate. Finally, results are shown for a freely vibrating cylinder under realistic flow and structural conditions. While a clear lock-in map is identified and shows good agreement with published numerical and experimental data, the work also highlights the unsteady nature of the aerodynamic forces and motion under certain operating conditions.
Highlights
Vortex-induced vibrations (VIVs) are structural vibrations that can occur due to the shedding of flow vortices when a fluid flow passes around a structure
The motion frequency equals the natural frequency in the lock-in region (i.e. ω/ωn = 1), whilst the frequency ratio follows the Strouhal relation outside the lock-in band. These results demonstrate that the present weakly coupled fluid– structure interaction (FSI) model is capable of predicting the dynamics of a light cylinder undergoing VIV in laminar flow conditions
The fluid–structure interaction methodology was validated in the laminar regime, for which direct numerical simulations (DNSs) were able to reproduce results from the literature
Summary
Vortex-induced vibrations (VIVs) are structural vibrations that can occur due to the shedding of flow vortices when a fluid flow passes around a structure. This effect is neglected, and circular cylinders are considered instead, with a focus on large Reynolds numbers Despite this limitation, the present study is relevant for the wind energy industry because of the interest of wind turbine developers in reducing the tapering at the top sections. Wind turbine towers experience flows both in the transitional regime (1.5 × 105× ≤ Re ≤ ×3.5 × 106), where laminar separation bubbles can exist and reduce the drag coefficient, and in the supercritical regime (Re ≥ 3.6×106), in which the boundary layer is fully turbulent.
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