Unsteady hydrodynamics of a full-scale tidal turbine operating in large wave conditions

Waves interact with currents in tidal channels with the resulting wave-current environment largely determining the loads experienced by tidal stream turbines. Over a tidal cycle, the magnitude and direction of the current velocity changes and hence so does the combined wave-current conditions the turbines must operate within. Here we demonstrate this effect experimentally, generating a realistic irregular wave case in both following (in the same direction as the waves) and opposing currents prior to assessing the resulting loads on a fully instrumented 1:15 scale tidal turbine model aligned with the current direction. Large changes in the environmental conditions, along with the turbine performance and loads, are demonstrated through the presentation of temporal, spectral and statistical outputs. The experimental results demonstrate that the full-scale equivalent significant wave height changes from 2.25 m in zero current to 6.11 m in 3.2 m/s opposing current and 1.56 m in 3.2m/s following current. The corresponding standard deviations of measured turbine parameters for the opposing condition range between 215 and 260% of the following case, and between 340 and 565% of the current-only measurements. Hence, when waves are present, significantly greater fatigue damage will be accumulated during one-half of the tidal cycle. The mean values, however, appear to be unaffected by the presence of waves suggesting that the overall turbine performance is unaltered. These results demonstrate the requirement to understand the combined wave-current environment and to test and de-risk tidal stream turbines for operation in both following and opposing wave-current conditions. Significant additional insight is gained into the nature of loads experienced by tidal turbines in irregular wave conditions, a scarcely documented phenomenon.

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“…Models incorporating dynamic stall (e.g. Scarlett et al 2018) will be used to increase insight into the phenomena.…”

Section: Comparison To Previous Results With Turbine Modelmentioning

confidence: 99%

Experimental assessment of tidal turbine loading from irregular waves over a tidal cycle

Draycott

Steynor

Nambiar

et al. 2019

J. Ocean Eng. Mar. Energy

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“…Dynamic stall load hysteresis loops are predicted using the model of Sheng et al [19], with a modification to account for rotational augmentation using the model of Lindenburg [20]. Full details of the model, including a validation case are described in Scarlett et al [7].…”

Section: Attached Flowmentioning

confidence: 99%

“…For a rotor blade the combination of blade rotation, which induces a centrifugal and Coriolis force on the flow, with dynamic stall can produce very large lift amplitudes compared to the non-rotational case [6,7].…”

Section: Introductionmentioning

confidence: 99%

“…The authors concluded that the effect of dynamic stall is limited and, therefore, can be neglected in some cases, despite not making comparison with quasi-steady values. In our recent study we quantified the loads for a fullscale, 1 MW horizontal axes tidal turbine operating in large wave conditions [7]. The loads, moments and power were modelled using measured flow velocity data from the European Marine Energy Center.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper we explore the different unsteady phenomena occurring along the blade span due to the shear layer, turbulence, waves and a yaw misalignment. Using our recently developed unsteady load model for arbitrary forcing [7], we identify the conditions which elicit the most significant load fluctuations and, for these conditions, how unsteadiness manifests along the span of the blade. We determine which blade section incurs the largest load fluctuations and whether added mass effects are amplifying or attenuating them.…”

Section: Introductionmentioning

confidence: 99%

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Unsteady hydrodynamics of tidal turbine blades

Scarlett

Viola

2020

Renewable Energy

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Tidal turbines encounter a range of unsteady flow conditions, some of which may induce severe load fluctuations. Rotor blades can experience stall delay, load hysteresis and dynamic stall. Yet, the range of flow conditions which cause these effects for a full-scale axial-flow turbine are unclear. In this work we carry out a parameter study across a range of flow conditions by modelling root bending moment responses. We show how unsteadiness manifests along the span of the blade, the unsteady phenomena occurring and the conditions which induce the most significant load fluctuations. We find that waves and turbulence are the main sources of unsteadiness, and that extreme waves dominate over extreme turbulence. A yaw misalignment increases the load fluctuations but reduces the maximum peak. Large yaw angles, low tip-speed ratios, and very large waves lead to dynamic stall increasing the mean loads. Conversely, added mass effects mostly attenuate the loadings.

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Large eddy simulations of a utility‐scale horizontal axis wind turbine including unsteady aerodynamics and fluid‐structure interaction modelling

2022

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Growing horizontal axis wind turbines are increasingly exposed to significant sources of unsteadiness, such as tower shadowing, yawed or waked conditions and environmental effects. Due to increased dimensions, the use of steady tabulated airfoil coefficients to determine the airloads along long blades can be questioned in those numerical fluid models that do not have the sufficient resolution to solve explicitly and dynamically the flow close to the blade. Various models exist to describe unsteady aerodynamics (UA). However, they have been mainly implemented in engineering models, which lack the complete capability of describing the unsteady and multiscale nature of wind energy. To improve the description of the blades' aerodynamic response, a 2D unsteady aerodynamics model is used in this work to estimate the airloads of the actuator line model in our fluid-structure interaction (FSI) solver, based on 3D large eddy simulation. At each section along the actuator lines, a semiempirical Beddoes-Leishman model includes the effects of noncirculatory terms, unsteady trailing edge separation, and dynamic stall in the dynamic evaluation of the airfoils' aerodynamic coefficients. The aeroelastic response of a utility-scale wind turbine under uniform, laminar and turbulent, sheared inflows is examined with oneand two-way FSI coupling between the blades' structural dynamics and local airloads, with and without the enhanced aerodynamics' description. The results show that the

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Unsteady hydrodynamics of a full-scale tidal turbine operating in large wave conditions

Cited by 40 publications

References 30 publications

Experimental assessment of tidal turbine loading from irregular waves over a tidal cycle

Experimental assessment of tidal turbine loading from irregular waves over a tidal cycle

Unsteady hydrodynamics of tidal turbine blades

Large eddy simulations of a utility‐scale horizontal axis wind turbine including unsteady aerodynamics and fluid‐structure interaction modelling

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