Flow over prismatic hull elements of floating wind turbines

Abstract

Platforms of floating offshore wind turbines, such as semi-submersible, tension leg and spar-buoy designs, consist in the vast majority of cases of cylindrical hull sections. However, would other cross-sectional shapes of the platform draft columns not be favourable when looking at the possible occurring flow-induced vibrations? In search for an answer, more than a dozen experimental wind tunnel studies have been conducted in the High-Pressure Wind Tunnel facility of the DLR Göttingen to investigate the unsteady flow and resulting fluid dynamics of circular cylinders and (rounded) square-section prisms in single and tandem configurations up to Reynolds numbers of 12 million. Governing and influencing parameters like the surface roughness height (i.e. the simulated coverage by marine fouling), edge roundness of the prism’s longitudinal edges, incidence angle, and gap spacing were varied and their decoupled and combined effects investigated. It will be shown that a variation of any of the above parameters can cause drastic fluid dynamic changes, with neither the cylindrical nor the prismatic hull element emerging as the overall big winner.