Large-Eddy Simulation of a Floating Offshore Wind Turbine with imposed motion
R.P.J. Combette (TU Delft - Aerospace Engineering)
Axelle Vire – Mentor (TU Delft - Wind Energy)
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Abstract
As the urge to decarbonise the energy field becomes increasingly important, a growing interest is shown in wind turbine technologies. In particular, the past few years have seen the development of floating offshore wind turbines for applications in deep waters.
In addition to the harsher environment they are facing, these wind turbines are mounted on floaters and therefore experience motions in the six additional degrees of freedom. As a result, this greatly alters their aerodynamic behaviour. The flow surrounding the rotor gains in complexity, becoming highly unsteady and three-dimensional. Thus, its resolution by numerical means calls for high-fidelity methods such as Large-Eddy Simulations (LES).
The objective of this study is to numerically impose single and coupled motions in the pitch and surge directions on a scale rotor of the DTU 10MW. This scale model was used for an experimental campaign within TU Delft, and particular interest is given to the comparison of the loads obtained.
Additionally, numerical simulations permit access to further information, such as the radial distribution of the loads or the wake development.
For this purpose, the LES code YALES 2 is used, implemented with an actuator line approach capable of dealing with imposed motions. Both 1-DOF and 2-DOF harmonic motions are imposed in the pitch and surge directions. Different reduced velocities and frequencies are considered.
On single-imposed surging motion, the loads are found to be well in accordance with the quasisteady theory (QST), even at high frequency, where much larger fluctuations were encountered during the experiment. Particular phenomena are also captured in the wake, such as the formation of vortex rings when the frequency is sufficiently high. Similar comments are made for 1-DOF pitching. Finally, for combined pitch/surge motions, the loads are also in accordance with the QST predictions made from the 1-DOF results. The influence of each motion on the wake’s development is also discussed.
Keywords: Floating offshore wind turbine (FOWT), Large-eddy simulation (LES), Actuator line method (ALM), Coupled imposed motions, pitch, surge