On the characteristics of the wake of a wind turbine undergoing large motions caused by a floating structure: an insight based on experiments and multi-fidelity simulations from the OC6 Phase III Project

Abstract

Abstract. This study reports the results of the second round of analyses of the OC6 project Phase III. While the first round investigated rotor aerodynamic loading, here focus is given to the wake behavior of a floating wind turbine under large motion. Wind tunnel experimental data from the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project are compared with the results of simulations provided by participants with methods and codes of different levels of fidelity. The effect of platform motion both on the near and the far wake is investigated. More specifically, the behavior of tip vortices in the near wake is evaluated through multiple metrics, such as streamwise position, core radius, convection velocity, and circulation. Additionally, the onset of velocity oscillations in the far wake is analyzed because this can have a negative effect on stability and loading of downstream rotors. Results in the near wake for unsteady cases confirm that simulations and experiments tend to diverge from the expected linearized quasi-steady behavior when the rotor reduced frequency increases over 0.5. Additionally, differences across the simulations become significant, suggesting that further efforts are required to tune the currently available methodologies in order to correctly evaluate the aerodynamic response of a floating wind turbine in unsteady conditions. Regarding the far wake, it is seen that, in some conditions, numerical methods over-predict the impact of platform motion on the velocity fluctuations. Moreover, results suggest that, different from original expectations about a faster wake recovery in a floating wind turbine, the effect of platform motion on the far wake seems to be limited or even oriented to the generation of a wake less prone to dissipation.

Going Beyond BEM with BEM: an Insight into Dynamic Inflow Effects on Floating Wind Turbines

“…This approach has shown to work well and was calibrated with respect to experiments, as shown in the results presented by Bergua et al (Bergua and et. al., 2023) and is able to resolve the tip vortex trajectory with accuracy similar to that of comparable numerical techniques (Cioni et al, 2023).…”

“…This process is commonly referred to as velocity sampling. In this work, the ALM code developed by coupling OpenFAST to the CFD solver CONVERGE (Richards et al, 2023), CALMA (Converge Actuator Line Model for Aeroelasticity) (Pagamonci et al, 2023) is used. In this code, velocity sampling is handled through the line-average velocity sampling algorithm proposed by Jost et al (Jost et al, 2018).…”

Experimental and CFD analysis of a floating offshore wind turbine under imposed motions

“…Further details on the ALM implementation in YALES2, as well as its validation on a fixedbottom wind turbine, are given in [7]. This implementation was later modified to account for motions in the six degrees of freedom and validated in [11].…”

OC6 Project Phase IV: Validation of Numerical Models for Novel Floating Offshore Wind Support Structures

“…The third phase (Bergua et al, 2022b) focused on validating the rotor aerodynamic loading for a FOWT undergoing large motions in the surge and pitch directions caused by the floating support structure. The implications of those large motions were also investigated for the near and far wake behavior (Cioni et al, 2023). The fourth phase is focused on validating the coupled dynamics of a novel floating wind design with a streamlined floating support structure, different from traditional FOWT designs.…”