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5 pages, 187 KiB

Open AccessEditorial

Tidal Turbines

by Sylvain S. Guillou and Eric Bibeau

Energies 2023, 16(7), 3204; https://doi.org/10.3390/en16073204 - 02 Apr 2023

Viewed by 980

Abstract

Tidal turbines generate energy from tidal currents [...] Full article

(This article belongs to the Special Issue Tidal Turbines)

Research

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13 pages, 707 KiB

Open AccessArticle

Assessment of Dependency of Unsteady Onset Flow and Resultant Tidal Turbine Fatigue Loads on Measurement Position at a Tidal Site

by Hannah Mullings and Tim Stallard

Energies 2021, 14(17), 5470; https://doi.org/10.3390/en14175470 - 02 Sep 2021

Cited by 11 | Viewed by 1473

Abstract

This work determines the variation in the fatigue loading on a tidal turbine at two depth positions and two different locations within a site. Site data were obtained at the European Marine Energy Centre, EMEC, test facility in Scotland, which has been compiled [...] Read more.

This work determines the variation in the fatigue loading on a tidal turbine at two depth positions and two different locations within a site. Site data were obtained at the European Marine Energy Centre, EMEC, test facility in Scotland, which has been compiled at the University of Edinburgh. The turbine modelled is the 18m Diameter DEEP-gen 1MW horizontal axis turbine. A blade element method is combined with a synthetic turbulence inflow to determine forces along the blade over a period of five tidal cycles. The focus is on establishing the difference between the loads at one tidal site, with an emphasis on the variety of turbulent conditions, with the onset flow fluctuations as great as 17% and the average integral lengthscales varying from 11 to 14 m at hub height. Fatigue loading is assessed using damage equivalent loads, with a 30% variation between turbine positions and 32% between turbine locations within a site, for one design case. When long term loading is assessed, a 41% difference is found for aggregated loads for a near surface turbine and a 28% difference for a near bed turbine. Full article

(This article belongs to the Special Issue Tidal Turbines)

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23 pages, 13690 KiB

Open AccessArticle

Study of a Bi-Vertical Axis Turbines Farm Using the Actuator Cylinder Method

by Laurie Jégo and Sylvain S. Guillou

Energies 2021, 14(16), 5199; https://doi.org/10.3390/en14165199 - 23 Aug 2021

Cited by 6 | Viewed by 1650

Abstract

Vertical axis turbines, which extract kinetic energy from currents, can produce electricity independently from a current’s direction. Hence, this type of turbines raises interest for harvesting energy from tidal currents, where flow changes direction during flood and ebb tides, and where currents present [...] Read more.

Vertical axis turbines, which extract kinetic energy from currents, can produce electricity independently from a current’s direction. Hence, this type of turbines raises interest for harvesting energy from tidal currents, where flow changes direction during flood and ebb tides, and where currents present large variation of direction during tide. Methods for representing vertical axis turbines in tidal farms should be implemented in order to predict correctly power production with an acceptable time cost. The Actuator Cylinder (AC) is one of them. Numerical results in terms of wakes, with the study of velocity profiles, and efforts are compared to experiences, as well as showed that the method is sufficiently accurate and for a reasonable computing time, which is of prime importance for tidal turbines farms studies. The Actuator Cylinder method is implemented in ANSYS Fluent in a 2D stationary resolution. The method is then applied to a double levels of two counter-rotating rotors marine turbine designed by Hydroquest. Wake and power production of a single turbine and several farm configurations are studied under different current conditions (magnitude and direction). Full article

(This article belongs to the Special Issue Tidal Turbines)

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19 pages, 10120 KiB

Open AccessArticle

Hydrodynamic Efficiency Analysis of a Flexible Hydrofoil Oscillating in a Moderate Reynolds Number Fluid Flow

by Paul Brousseau, Mustapha Benaouicha and Sylvain Guillou

Energies 2021, 14(14), 4370; https://doi.org/10.3390/en14144370 - 20 Jul 2021

Cited by 6 | Viewed by 2345

Abstract

The paper focuses on the study of a semi-activated system, based on a combination of two movements of forced pitching and free-heaving motion. Therefore, quantifying with accuracy the hydrodynamic forces applied on the hydrofoil seems to be crucial. This is investigated throughout a [...] Read more.

The paper focuses on the study of a semi-activated system, based on a combination of two movements of forced pitching and free-heaving motion. Therefore, quantifying with accuracy the hydrodynamic forces applied on the hydrofoil seems to be crucial. This is investigated throughout a numerical analysis of the hydrofoil dynamics. The deformable structure is oscillating in a low-Reynolds number flow. In this study, a hydrofoil animated by a combined forced pitching and heaving movements is considered. Various materials of the hydrofoil structure are studied, from the rigid material to a more flexible one. A partitioned implicit coupling approach is applied in order to consider the Fluid-Structure Interaction (FSI) effects, while the Navier–Stokes equations are solved using the Arbitrary Lagrangian–Eulerian (ALE) method. Both the viscous incompressible Navier–Stokes equations and the elasticity equation are solved using finite volume method. The study is based on the analysis of the hydrodynamic loads acting on the structure. Therefore, the induced dynamics and the power coefficient of the structure are investigated. It is shown that the flexibility of the hydrofoil has an effect on its hydrodynamic behavior. Indeed it increases the load fluctuations and the horizontal mean force component. Furthermore, the unsteady vortices around the hydrofoil are highly impacted by its deformations. Finally, the structure deformations mostly improve the device energy efficiency. Full article

(This article belongs to the Special Issue Tidal Turbines)

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16 pages, 4141 KiB

Open AccessArticle

Research on Blade Design of Lift–Drag-Composite Tidal-Energy Turbine at Low Flow Velocity

by Chuhua Jiang, Xuedao Shu, Junhua Chen, Lingjie Bao and Yawen Xu

Energies 2021, 14(14), 4258; https://doi.org/10.3390/en14144258 - 14 Jul 2021

Cited by 4 | Viewed by 1989

Abstract

The research on tidal-current energy-capture technology mainly focuses on the conditions of high flow velocity, focusing on the use of differential pressure lift, while the average flow velocity in most sea areas of China is less than 1.5 m/s, especially in the marine [...] Read more.

The research on tidal-current energy-capture technology mainly focuses on the conditions of high flow velocity, focusing on the use of differential pressure lift, while the average flow velocity in most sea areas of China is less than 1.5 m/s, especially in the marine aquaculture area, where tidal-current energy is needed to provide green energy locally. Due to the low flow velocity of this type of sea area, it seriously affects the effect of differential pressure lift, which is conducive to exerting the effect of impact resistance. In this regard, the coupling effect of the differential pressure lift and the impact resistance on the blade torque is comprehensively considered, this research puts forward the design method of the lift-–drag-composite thin-plate arc turbine blade. Based on the blade element momentum (BEM) theory and Bernoulli’s principle, the turbine dynamic model was established, and the nonlinear optimization method was used to solve the shape parameters of the turbine blades, and the thin-plate arc and NACA airfoil blade turbines were trial-produced under the same conditions. A model experiment was carried out in the experimental pool, and the Xiangshan sea area in Ningbo, East China Sea was taken as the experimental sea area. The results of the two experiments showed the same trend, indicating that the energy-harvesting performance of the lift–drag-composite blade was significantly better than that of the lift blade under the conditions of low flow velocity and small radius, which verified the correctness of the blade design method, and can promote the research and development of tidal energy under the conditions of low flow velocity and small radius. Full article

(This article belongs to the Special Issue Tidal Turbines)

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23 pages, 4437 KiB

Open AccessArticle

Lagrangian Vortex Computations of a Four Tidal Turbine Array: An Example Based on the NEPTHYD Layout in the Alderney Race

by Myriam Slama, Camille Choma Bex, Grégory Pinon, Michael Togneri and Iestyn Evans

Energies 2021, 14(13), 3826; https://doi.org/10.3390/en14133826 - 25 Jun 2021

Cited by 5 | Viewed by 1427

Abstract

This study investigates the wake interaction of four full-scale three-bladed tidal turbines with different ambient turbulence conditions, in straight and yawed flows. A three-dimensional unsteady Lagrangian Vortex Blob software is used for the numerical simulations of the turbines’ wakes. In order to model [...] Read more.

This study investigates the wake interaction of four full-scale three-bladed tidal turbines with different ambient turbulence conditions, in straight and yawed flows. A three-dimensional unsteady Lagrangian Vortex Blob software is used for the numerical simulations of the turbines’ wakes. In order to model the ambient turbulence in the Lagrangian Vortex Method formalism, a Synthetic Eddy Method is used. With this method, turbulent structures are added in the computational domain to generate a velocity field which statistically reproduces any ambient turbulence intensity and integral length scale. The influence of the size of the structures and their density (within the study volume) on the wake of a single turbine is studied. Good agreement is obtained between numerical and experimental results for a high turbulence intensity but too many structures can increase the numerical dissipation and reduce the wake extension. Numerical simulations of the four turbine array with the layout initially proposed for the NEPTHYD pilot farm are then presented. Two ambient turbulence intensities encountered in the Alderney Race and two integral length scales are tested with a straight flow. Finally, the wakes obtained for yawed flows with different angles are presented, highlighting turbine interactions. Full article

(This article belongs to the Special Issue Tidal Turbines)

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17 pages, 12502 KiB

Open AccessArticle

Quantifying the Effects of Wave—Current Interactions on Tidal Energy Resource at Sites in the English Channel Using Coupled Numerical Simulations

by Jon Hardwick, Ed B. L. Mackay, Ian G. C. Ashton, Helen C. M. Smith and Philipp R. Thies

Energies 2021, 14(12), 3625; https://doi.org/10.3390/en14123625 - 18 Jun 2021

Cited by 4 | Viewed by 1865

Abstract

Numerical modeling of currents and waves is used throughout the marine energy industry for resource assessment. This study compared the output of numerical flow simulations run both as a standalone model and as a two-way coupled wave–current simulation. A regional coupled flow-wave model [...] Read more.

Numerical modeling of currents and waves is used throughout the marine energy industry for resource assessment. This study compared the output of numerical flow simulations run both as a standalone model and as a two-way coupled wave–current simulation. A regional coupled flow-wave model was established covering the English Channel using the Delft D-Flow 2D model coupled with a SWAN spectral wave model. Outputs were analyzed at three tidal energy sites: Alderney Race, Big Roussel (Guernsey), and PTEC (Isle of Wight). The difference in the power in the tidal flow between coupled and standalone model runs was strongly correlated to the relative direction of the waves and currents. The net difference between the coupled and standalone runs was less than 2.5%. However, when wave and current directions were aligned, the mean flow power was increased by up to 7%, whereas, when the directions were opposed, the mean flow power was reduced by as much as 9.6%. The D-Flow Flexible Mesh model incorporates the effects of waves into the flow calculations in three areas: Stokes drift, forcing by radiation stress gradients, and enhancement of the bed shear stress. Each of these mechanisms is discussed. Forcing from radiation stress gradients is shown to be the dominant mechanism affecting the flow conditions at the sites considered, primarily caused by dissipation of wave energy due to white-capping. Wave action is an important consideration at tidal energy sites. Although the net impact on the flow power was found to be small for the present sites, the effect is site specific and may be significant at sites with large wave exposure or strong asymmetry in the flow conditions and should thus be considered for detailed resource and engineering assessments. Full article

(This article belongs to the Special Issue Tidal Turbines)

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17 pages, 1072 KiB

Open AccessArticle

Tidal Stream vs. Wind Energy: The Value of Cyclic Power When Combined with Short-Term Storage in Hybrid Systems

by Daniel Coles, Athanasios Angeloudis, Zoe Goss and Jon Miles

Energies 2021, 14(4), 1106; https://doi.org/10.3390/en14041106 - 19 Feb 2021

Cited by 20 | Viewed by 4337

Abstract

This study quantifies the technical, economic and environmental performance of hybrid systems that use either a tidal stream or wind turbine, alongside short-term battery storage and back-up oil generators. The systems are designed to partially displace oil generators on the island of Alderney, [...] Read more.

This study quantifies the technical, economic and environmental performance of hybrid systems that use either a tidal stream or wind turbine, alongside short-term battery storage and back-up oil generators. The systems are designed to partially displace oil generators on the island of Alderney, located in the British Channel Islands. The tidal stream turbine provides four power generation periods per day, every day. This relatively high frequency power cycling limits the use of the oil generators to 1.6 GWh/year. In contrast, low wind resource periods can last for days, forcing the wind hybrid system to rely on the back-up oil generators over long periods, totalling 2.4 GWh/year (50% higher). For this reason the tidal hybrid system spends £0.25 million/year less on fuel by displacing a greater volume of oil, or £6.4 million over a 25 year operating life, assuming a flat cost of oil over this period. The tidal and wind hybrid systems achieve an oil displacement of 78% and 67% respectively (the same as the reduction in carbon emissions). For the wind hybrid system to displace the same amount of oil as the tidal hybrid system, two additional wind turbines are needed. The ability of the battery to store excess turbine energy during high tidal/wind resource periods relies on opportunities to regularly discharge stored energy. The tidal hybrid system achieves this during slack tides. Periods of high wind resource outlast those of high tidal resource, causing the battery to often remain fully charged and excess wind power to be curtailed. Consequently the wind hybrid system curtails 1.9 GWh/year, whilst the tidal turbine curtails 0.2 GWh/year. The ability of the tidal stream turbines to reduce curtailment, fuel costs and carbon emissions may provide a case for implementing them in hybrid systems, if these benefits outweigh their relatively high capital and operating expenditure. Full article

(This article belongs to the Special Issue Tidal Turbines)

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13 pages, 5682 KiB

Open AccessArticle

The Efficiency of a Fence of Tidal Turbines in the Alderney Race: Comparison between Analytical and Numerical Models

by Jérôme Thiébot, Nasteho Djama Dirieh, Sylvain Guillou and Nicolas Guillou

Energies 2021, 14(4), 892; https://doi.org/10.3390/en14040892 - 09 Feb 2021

Cited by 5 | Viewed by 1754

Abstract

Assessing the efficiency of a tidal turbine array is necessary for adequate device positioning and the reliable evaluation of annual energy production. Array efficiency depends on hydrodynamic characteristics, operating conditions, and blockage effects, and is commonly evaluated by relying on analytical models or [...] Read more.

Assessing the efficiency of a tidal turbine array is necessary for adequate device positioning and the reliable evaluation of annual energy production. Array efficiency depends on hydrodynamic characteristics, operating conditions, and blockage effects, and is commonly evaluated by relying on analytical models or more complex numerical simulations. By applying the conservations of mass, momentum, and energy in an idealized flow field, analytical models derive formulations of turbines’ thrust and power as a function of the induction factor (change in the current velocity induced by turbines). This simplified approach also gives a preliminary characterization of the influence of blockage on array efficiency. Numerical models with turbines represented as actuator disks also enable the assessment of the efficiency of a tidal array. We compare here these two approaches, considering the numerical model as a reference as it includes more physics than the analytical models. The actuator disk approach is applied to the three-dimensional model Telemac3D in realistic flow conditions and for different operating scenarios. Reference results are compared to those obtained from three analytical models that permit the investigation of the flow within tidal farm integrating or excluding processes such as the deformation of the free surface or the effects of global blockage. The comparison is applied to the deployment of a fence of turbines in the Alderney Race (macro-tidal conditions of the English Channel, northwest European shelf). Efficiency estimates are found to vary significantly from one model to another. The main result is that analytical models predict lower efficiency as they fail to approach realistically the flow structure in the vicinity of turbines, especially because they neglect the three-dimensional effects and turbulent mixing. This finding implies that the tidal energy yield potential could be larger than previously estimated (with analytical models). Full article

(This article belongs to the Special Issue Tidal Turbines)

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17 pages, 14766 KiB

Open AccessArticle

Cross-Flow Tidal Turbines with Highly Flexible Blades—Experimental Flow Field Investigations at Strong Fluid–Structure Interactions

by Stefan Hoerner, Iring Kösters, Laure Vignal, Olivier Cleynen, Shokoofeh Abbaszadeh, Thierry Maître and Dominique Thévenin

Energies 2021, 14(4), 797; https://doi.org/10.3390/en14040797 - 03 Feb 2021

Cited by 9 | Viewed by 2774

Abstract

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single [...] Read more.

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single tip-speed ratio (equal to 2), the key non-dimensional parameter describing the operating point, and solidity (equal to 1.5), quantifying the robustness of the turbine shape. Both parameters are standard values for cross-flow tidal turbines. Those lead to highly dynamic characteristics in the flow field dominated by dynamic stall. The flow field is investigated at the blade level using high-speed particle image velocimetry measurements. Strong fluid–structure interactions lead to significant structural deformations and highly modified flow fields. The flexibility of the blades is shown to significantly reduce the duration of the periodic stall regime; this observation is achieved through systematic comparison of the flow field, with a quantitative evaluation of the degree of chaotic changes in the wake. In this manner, the study provides insights into the mechanisms of the passive flow control achieved through blade flexibility in cross-flow turbines. Full article

(This article belongs to the Special Issue Tidal Turbines)

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18 pages, 1522 KiB

Open AccessArticle

Performance Improvement of a Darrieus Tidal Turbine with Active Variable Pitch

by Pierre-Luc Delafin, François Deniset, Jacques André Astolfi and Frédéric Hauville

Energies 2021, 14(3), 667; https://doi.org/10.3390/en14030667 - 28 Jan 2021

Cited by 15 | Viewed by 2257

Abstract

Vertical axis turbines, also called Darrieus turbines, present interesting characteristics for offshore wind and tidal applications but suffer from vibrations and a lower efficiency than the more conventional horizontal axis turbines. The use of variable pitch, in order to control the angle of [...] Read more.

Vertical axis turbines, also called Darrieus turbines, present interesting characteristics for offshore wind and tidal applications but suffer from vibrations and a lower efficiency than the more conventional horizontal axis turbines. The use of variable pitch, in order to control the angle of attack of the blades continuously during their rotation, is considered in this study to overcome these problems. 2D blade-resolved unsteady Reynolds-Averaged Navier–Stokes (RANS) simulations are employed to evaluate the performance improvement that pitching blades can bring to the optimal performance of a three-straight-blade vertical axis tidal turbine. Three pitching laws are defined and tested. They aim to reduce the angle of attack of the blades in the upstream half of the turbine. No pitching motion is used in the downstream half. The streamwise velocity, monitored at the center of the turbine, together with the measurement of the blades’ angle of attack help show the effectiveness of the proposed pitching laws. The decrease in the angle of attack in the upstream half of a revolution leads to a significant increase in the power coefficient (

+ 40 %

) and to a better balance of the torque generated in the upstream and downstream halves. Both torque and thrust ripples are therefore significantly reduced. Full article

(This article belongs to the Special Issue Tidal Turbines)

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16 pages, 5981 KiB

Open AccessArticle

A Fuzzy Adaptative Backstepping Control Strategy for Marine Current Turbine under Disturbances and Uncertainties

by Xusheng Shen, Tao Xie and Tianzhen Wang

Energies 2020, 13(24), 6550; https://doi.org/10.3390/en13246550 - 11 Dec 2020

Cited by 8 | Viewed by 2154

Abstract

Marine current energy is attracting more and more attention in the world as a reliable and highly predictable energy resource. However, conventional proportional integral (PI) control will be sensitive to the numerous challenges that exist in a marine current turbine system (MCTs) such [...] Read more.

Marine current energy is attracting more and more attention in the world as a reliable and highly predictable energy resource. However, conventional proportional integral (PI) control will be sensitive to the numerous challenges that exist in a marine current turbine system (MCTs) such as marine current disturbance, torque disturbance and other uncertain parameters. This paper proposes a fuzzy adaptive backstepping control (F-A-BC) approach for a marine current turbine system. The proposed F-A-BC strategy consisted of two parts. First, an adaptive backstepping control approach with the compensation of disturbance and uncertainty was designed to improve anti-interference of the MCT so that the maximum power point tracking (MPPT) was realized. Then, a fuzzy logic control approach was combined to adjust parameters of an adaptive backstepping control approach in real time. The effectiveness of the proposed controller was verified by the simulation of a direct-drive marine current turbine system. The simulation results showed that the F-A-BC has better anti-interference ability and faster convergence compared to the adaptive backstepping control, sliding mode control and fuzzy PI control strategies under disturbances. The error percentage of rotor speed could be reduced by 3.5% under swell effect compared to the conventional controller. Moreover, the robustness of the F-A-BC method under uncertainties was tested and analyzed. The simulation results also indicated that the proposed approach could slightly improve the power extraction capability of the MCTs under variable marine current speed. Full article

(This article belongs to the Special Issue Tidal Turbines)

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14 pages, 3991 KiB

Open AccessArticle

Research on Performance Evaluation of Tidal Energy Turbine under Variable Velocity

by Chuhua Jiang, Xuedao Shu, Junhua Chen, Lingjie Bao and Hao Li

Energies 2020, 13(23), 6313; https://doi.org/10.3390/en13236313 - 30 Nov 2020

Cited by 3 | Viewed by 1733

Abstract

Aiming at the performance evaluation problem of tidal energy turbines in the application of periodic time-varying flow velocity, with the goal of maximizing the efficiency of energy harvesting in practical applications, an evaluation system combining the characteristics of flow velocity changes in practical [...] Read more.

Aiming at the performance evaluation problem of tidal energy turbines in the application of periodic time-varying flow velocity, with the goal of maximizing the efficiency of energy harvesting in practical applications, an evaluation system combining the characteristics of flow velocity changes in practical applications is proposed. After long-term monitoring of tidal current flow velocity in the applied sea area, the actual measured tidal current periodic flow velocity is divided into several flow velocity segments by using statistical segmentation, and the evaluation flow velocity of each flow velocity segment and its time proportion in the tidal current cycle are obtained. A test device with constant torque regulation is built, and capture power tests of different torque loads are carried out under each evaluation flow rate. After comparison, the maximum captured power at each evaluation flow rate is determined. We calculate the weight based on the time proportion of each evaluation flow velocity and obtain the turbine average power of the tidal cycle, thereby evaluating the overall energy capture performance of the turbine under the periodic time-varying flow velocity. Finally, the application test of the turbine in the actual sea area shows that the thin-walled airfoil turbine is more suitable for the sea area, which is the same as the pool evaluation result. The result shows that the evaluation system is reliable and effective and has significance for guiding practical engineering. Full article

(This article belongs to the Special Issue Tidal Turbines)

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