Abstract

Floating Offshore Wind Turbines may experience large surge motions which, when faster than the local wind speed, cause rotor-wake interaction. Previous research hypothesised that this phenomena can result in a turbulent wake state or even a vortex ring state, invalidating the Actuator Disc Momentum Theory and the use of the Blade Element Momentum Theory. We challenge this hypothesis and demonstrate that the Actuator Disc Momentum Theory is valid and accurate in predicting the induction at the actuator in surge, even for large and fast motions. To achieve this, we derive a dynamic inflow model which mimics the vorticity-velocity system and the effect of the motion. The predictions of the model are compared against results from other authors and from a semi-free wake vortex-ring model. The results show that the surge motion and rotor-wake interaction do not cause a turbulent wake state or vortex ring state, and that the application of Actuator Disc Momentum Theory and Blade Element Momentum Theory is valid and accurate, when correctly applied in an inertial reference frame. The results show excellent agreement in all cases. The proposed dynamic inflow model includes an adaptation for highly loaded flow and it is accurate and simple enough to be easily implemented in most Blade Element Momentum models.

Highlights

  • 1.1 Motivation for the research 15 Floating offshore wind turbines (FOWTs) are placed on floating foundations, which leads to larger motions than wind turbines on bottom mounted foundations

  • The results show that the surge motion and rotor-wake interaction do not cause a turbulent wake state or vortex ring state, and that the application of Actuator Disc Momentum Theory and Blade Element Momentum Theory is valid and accurate, when correctly applied in an inertial reference frame

  • 140 The results presented and discussed in the Section Results and Discussion have three sources: the Navier-Stokes simulations of an actuator disc in surge by de Vaal et al (2014); simulations by a semi-free wake vortex-ring model of an actuator disc in surge motion developed in this work; and a 1D Actuator Disc Momentum model corrected for the unsteady surge motion and loading by using a dynamic inflow model derived in this work

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Summary

Introduction

1.1 Motivation for the research 15 Floating offshore wind turbines (FOWTs) are placed on floating foundations, which leads to larger motions than wind turbines on bottom mounted foundations (de Vaal et al, 2014) This increased freedom of motion can result in several phenomena of unsteady aerodynamics at airfoil, blade, rotor and wake scale, studied by Sebastian and Lackner (2012), Sebastian and Lackner (2013), Sivalingam et al (2018), Kyle et al (2020), Wen et al (2017), Lee and Lee (2019), de Vaal et al (2014), Mancini et al (2020), Micallef and Sant (2015), Tran and Kim (2016), Chen et al (2021), Shen et al (2018), Lee and Lee (2019), Farrugia 20 et al (2016), Cormier et al (2018), Dong et al (2019), Dong and Viré (2021) and others.

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