Session: 41-04 Offshore wind

Submission Number: 176852

Wind Tunnel Characterization of Wake Development Behind a Floating Troposkein Vertical Axis Wind Turbine Model 

Floating offshore wind energy based on horizontal-axis wind turbines (HAWTs) currently exhibits a higher Levelized Cost of Energy (LCOE) compared to onshore systems, mainly due to elevated installation and maintenance costs. Vertical-axis wind turbines (VAWTs) represent a promising alternative for offshore applications thanks to several advantages: they are insensitive to wind direction and can be scaled to multi-megawatt power ratings, they do not require yaw or pitch actuators, which reduces mechanical complexity and failure risk; placing the generator at the base lowers the turbine’s center of gravity, allowing for a smaller floating platform, typically accounting for around 60% of the Capital Expenditure (CAPEX) offering a pathway to lower the overall cost of floating offshore wind energy.

Furthermore, it is expected that the wake shed by VAWT exhibits a more rapid recovery with respect to conventional HAWT, potentially leading to wind farm characterized by higher power density. Since comparative studies of wake recovery between HAWTs and VAWTs have not produced definitive conclusions further research is needed to deepen the understanding of VAWT wake dynamics, particularly involving wave-induced oscillations. While load prediction models for fixed-bottom VAWTs are well established, they lack validation against experimental data for floating configurations. Although these models can provide reliable estimates of average loads, the load amplitudes transferred to turbine supports must be assessed, as they directly affect the fatigue life of mechanical components. Additionally, wake models developed for HAWTs cannot be directly applied to VAWTs because the underlying wake mechanisms differ, and floating motions can amplify these effects. Physical modeling of VAWT wakes is therefore essential to provide benchmarks for numerical simulations and to support Levelized Cost of Energy assessments for floating wind farms.

To address this gap, a new Troposkein rotor, featuring a 1.5 m diameter in the equatorial section, has been designed and tested in the Galleria del Vento of Politecnico di Milano (GVPM) under both fixed and surge conditions, to characterize wake development from 1.5D to 7.5D downstream, thus providing considerable new information on the impact and potential of these machines.  The turbine model was mounted on a six-degree-of-freedom robotic platform (HexaFloat), enabling prescribed surge motions with controlled frequency and amplitude. The results show that the wake is deflected toward the windward side of the rotor, indicating a natural wake steering effect which should be accounted for when designing and optimizing wind farm layout. Notably, surge motion promotes wake recovery by more than 10% compared to the fixed-bottom case at 3.5D downstream, with the difference slightly increasing further downstream. Preliminary results highlight the capability of Troposkein VAWTs to mitigate wake deficits, supporting reduced inter-array spacing and higher installed power density in future floating wind farms.

Presenting Author: Alberto Fusetti Politecnico di Milano

Presenting Author Biography: *

Authors:

Alberto Fusetti Politecnico di Milano
Claudio Tomassoni Politecnico di Milano
Andrea Giuseppe Sanvito Politecnico di Milano
Alessandro Fontanella Politecnico di Milano
Giacomo Persico Politecnico di Milano
Vincenzo Dossena Politecnico di Milano