The aerodynamic interference effects of a floating offshore wind turbine experiencing platform pitching and yawing motions

Over the last decade, several coupled simulation tools have been developed in order to design and optimize floating wind turbines (FWTs). In most of these tools, the aerodynamic modeling is based on quasi‐steady aerodynamic models such as the blade element momentum (BEM). It may not be accurate enough for FWTs as the motion of the platform induces highly unsteady phenomena around the rotor. To address this issue, a new design tool has been developed coupling a seakeeping solver with an unsteady aerodynamic solver based on the free vortex wake (FVW) theory. This tool is here compared with the reference code FAST, which is based on the BEM theory in order to characterize the impact of the aerodynamic model on the seakeeping of a floating horizontal axis wind turbine (HAWT). Aerodynamic solvers are compared for the case of the free floating NREL 5MW HAWT supported by the OC3Hywind SPAR. Differences obtained between the models have been analyzed through a study of the aerodynamic loads acting on the same turbine in imposed harmonic surge and pitch motions. This provides a better understanding of the intrinsic differences between the quasi‐steady and unsteady aerodynamic solvers. The study shows that differences can be observed between the three aerodynamic solvers, especially at high tip speed ratio (TSR) for which unsteady aerodynamic phenomena and complex wake dynamics occur. Observed discrepancies in the predictions of the FWT dynamic response can raise issues when designing such a system with a state‐of‐the‐art design tool.

“…The rotor then operates at even higher TSR and hence strongly interacts with its wake. () This can lead to highly unsteady phenomena that are not accounted for in the BEM method.…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Impact of aerodynamic modeling on seakeeping performance of a floating horizontal axis wind turbine

Leroy

Gilloteaux

Lynch³

et al. 2019

“…The FOWT simulations considering the prescribed pitching, yawing, and surge motions were well demonstrated in our previous studies. 36,37,47,48 The good agreement of predicted aerodynamic power and thrust between CFD and conventional analysis tools was illustrated for cases when the apparent wind due to these floating motions is small. The difference between them increases as the apparent wind increases.…”

Section: Computational Fluid Dynamicsmentioning

confidence: 93%

A CFD study of coupled aerodynamic‐hydrodynamic loads on a semisubmersible floating offshore wind turbine

Tran

Kim

2017

Self Cite

The prediction of dynamic characteristics for a floating offshore wind turbine (FOWT) is challenging because of the complex load coupling of aerodynamics, hydrodynamics, and structural dynamics. These loads should be accurately calculated to yield reliable analysis results in the design phase of a FOWT. In this study, a high-fidelity fluid-structure interaction simulation that simultaneously considers the influence of aero-hydrodynamic coupling due to the dynamic motion of a FOWT has been conducted using computational fluid dynamics based on an overset The dynamic influence of aero-hydro-structure interaction due to the coupled wind-wave loads on a floating offshore wind turbine (FOWT) is still not well understood. Various experimental floating substructures in both wave basin facilities and ocean coasts have been constructed or are in the planning stages throughout the world. 1-7 The current status of both of them is well described in the previous studies. [2][3][4] From the viewpoint of engineering, compared to a full-scale test on an ocean field, a wave basin test for a scaled-down model can reduce risk, cost, and uncertainties in the design. Dynamic characteristics of floating structure from a wave basin test can be approximately evaluated. However, its results are highly influenced by purpose of tests and quality of experiment equipment (eg, installed sensors and wind and wave generation quality). Moreover, previous experimental works did not adequately consider the same material, construction methods, or deployment method as the full-scale system. 7 In particular, a scaled-down model experiment in a wave basin inherently has limitations on the simultaneous satisfaction of both Froude and Reynolds scaling laws. [8][9][10][11] The scaled-down model is typically scaled by the dimensionless Froude number to ensure the similarity of platform hydrodynamic whereas the tip-speed ratio and wind speed to wave celerity ratio between scales is maintained to entirely consistent with Froude scaling. 8 However, an experiment on a FOWT is usually more expensive than a sophisticated design tool, which is preferred for cost-effective solutions during the design process. Therefore, sophisticated modeling tools must be developed to accurately simulate the complex multiphysical phenomena induced by aero-hydro-multibody dynamic coupling for a FOWT. 1 The dynamic characteristics of FOWTs have been properly analyzed by fully coupled aero-hydro-servo-elastic dynamic approaches. [12][13][14] However, the unsteady aerodynamic calculation in these approaches was performed using the well-known blade element momentum (BEM)

“…Recently, many investigations have been performed with the aim of exploring the effects of platform motion on the aerodynamic performance of OFWTs, especially for the case of platform pitching motion. Tran and Kim have studied the pitching motion of OFWTs using a computational fluid dynamic (CFD) approach. It is revealed that the aerodynamic loads of the OFWT are sensitive to platform motions.…”

Section: Introductionmentioning

confidence: 99%

Effect of platform disturbance on the performance of offshore wind turbine under pitch control

Aliabadi

Rasekh

2020

The aerodynamic performance of offshore floating wind turbines (OFWTs) is more complicated than onshore wind turbines due to 6-degree of freedom (DOF) motion of the floating platform. In the current study, the aerodynamic analysis of a horizontal-axis floating offshore wind turbine is performed with the aim of studying the effects of floating platform movement on the aerodynamic characteristics of the turbine in the presence of a pitch angle control system. The National Renewable Energy Laboratory (NREL) 5-MW offshore wind turbine is selected as the baseline wind turbine. For this sake, the unsteady blade element momentum method with dynamic stall and dynamic inflow models have been employed to obtain the unsteady aerodynamic loads. The baseline pitch angle control system is assumed to be coupled with the aerodynamic model to maintain the rated condition of the wind turbine and also to approach a closer model of wind turbine. In case of pitching motion input, the reduction of mean power coefficient for tip speed ratios (TSRs) less that 7 is expected by an amount of 16% to 20% at pitch amplitude of 2 and frequency of 0.1 Hz. For high TSRs, the trend is reverse with respect to fixed-platform case. The mean thrust coefficient is reduced for almost all range of TSRs with maximum loss of 37%.Moreover, the mean control pitch angle that is an index of control system effort is increased. The results also represent the importance of considering the pitch control system for aerodynamic analysis of disturbed OFWT. K E Y W O R D Sfloating offshore wind turbine, pitch, pitch control system, platform disturbance, unsteady blade element momentum method 1 | INTRODUCTION Nowadays, the numerous advantages of offshore wind turbines (OWTs) lead us to use them in order to harvest energy from offshore wind.Although the construction and installation of OWTs are more expensive than the onshore wind farms, the availability of space and fewer complaints about noise problems make them more attractive compared with the onshore wind turbines. 1 Moreover, the wind energy potential is considerable at offshore. Statistics 2,3 show that the rated capacity of OWTs has grown 62% over the past decade, particularly the mean rated capacity of OWTs has increased about 15.4% from 2015 to 2016.The foundation type of the OWT depends on the sea depth, which could be either fixed or floated. In deep-sea area, the floating platform is utilized instead of fixed-foundation technology. Due to the waves and currents in sea regions, offshore floating wind turbines (OFWTs)