Morphing-Blades: New-Concept Turbine Blades for Unsteady Load Mitigation

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Engineering

Abstract

This project aims to demonstrate at model-scale a novel technology to reduce unsteady-loading for tidal turbines, improving resilience and reliability, and decreasing the levelised cost of energy.

Tidal energy is a promising renewable energy source that can contribute to providing energy security to the UK. The first and second array of tidal turbines has now been deployed in Scotland, confirming the UK as a world leader in this emerging energy sector. One of the main technical challenges of harvesting energy from tidal currents is the large load fluctuations experienced by the blades. These can result in fatigue failures of the blades and in power fluctuations at the generator that must be smoothed before power can be provided to the grid. The aim of this project is to develop a technology that cancels the unsteady loading at its source, while adding minimal complexity to the turbine to ensure high resilience and reliability of the overall system.

The technology currently adopted to mitigate load fluctuations in air, such as that one employed by wind turbines and aerial vehicles, is not directly transferable to tidal turbines because of the harsh marine environment and the high hydrodynamic loads. For example, complex systems requiring hinges with bearings would be subjected to fouling and would reduce the blade reliability. To address this issue, we would consider introducing local flexibility that does not affect the key structural elements of the blade, and whose displacement can mitigate load fluctuations. The lowest loaded part of the blade is the trailing edge, and this is also where the smallest shape morphing can lead to the largest changes in the overall load. We could manufacture a blade made of the same material as a conventional rigid blade (fibreglass) but with a structural design that allows the trailing edge to bend to react to flow changes. To ensure high reliability of the system, we could exploit passive deformation without sensors and actuators. The small inertia of the part of the blade that bends would enable a prompt reaction to flow fluctuations.

Our preliminary studies showed that a blade with a flexible trailing edge can theoretically mitigate more than 90% of the load fluctuations without affecting the mean power output. This project aims to verify these initial results by testing model-scale prototypes. We aim to design and manufacture two sets of 0.6 m and 1.2 m span blades to undertake fluid dynamics tests on a model-scale turbine and fatigue tests, respectively. These tests will demonstrate the efficacy, robustness, resiliency and reliability of morphing blades.

The project includes key tidal and wind energy technology companies: SIMEC Atlantis Energy, Orbital Marine Power, Nautricity, Nova Innovation, Schottel Hydro, ACT Blades and Wood Group. Together with these industrial partners we aim to investigate the applicability of morphing blades to different tidal technologies, from 70 kW to 2 MW, from 4 m to 20 m diameter, and both seabed mounted and floating turbines with single and multi rotors. If proven effective for tidal turbines, we would also explore with our wind energy partners (ACT Blades and Wood Group) whether this technology is suitable to complement or replace some of the existing unsteady load mitigation technology currently adopted by wind turbines. Morphing blades could contribute to reduce fatigue loads, to increase reliability and lifetime yield, and hence to reduce the levelised cost of energy. It is envisaged that this technology could be more suitable for offshore wind turbines than onshore wind turbines because of the higher relative importance of component reliability.

Overall this project aims to investigate the suitability of morphing blades to mitigate unsteady loads on tidal turbines, aiming at decreasing costs of blades and increase the energy yields, and thus decrease the overall cost of tidal energy.

Publications

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Arredondo-Galeana A (2022) A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers in Journal of Marine Science and Engineering

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Arredondo-Galeana A (2021) Unsteady load mitigation through a passive trailing-edge flap in Journal of Fluids and Structures

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Dai W (2022) Mitigation of rotor thrust fluctuations through passive pitch in Journal of Fluids and Structures

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Pisetta G (2022) Morphing blades for tidal turbines: A theoretical study in Renewable Energy

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Viola I (2022) Underwater LED-based Lagrangian particle tracking velocimetry in Journal of Visualization

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Viola I (2022) Morphing Blades Theory and Proof of Principles in International Marine Energy Journal

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Viola I.M. (2021) Morphing blades: Theory and proof of principles in Proceedings of the European Wave and Tidal Energy Conference

 
Description Tidal currents are renewable and predictable energy sources that could prove fundamental to the transition to sustainable use of renewable energy resources. Over a tidal period, changes in the flow speed in a tidal channel require that the blade pitch be adjusted to maximise power extraction. This is currently achieved with active pitch actuation, which, however, increases the capital and maintenance cost of the turbine. Furthermore, because of turbulence in the tidal stream, turbine yaw, wave-induced currents, etc., tidal turbine blades experience high-frequency velocity fluctuations that result in power and thrust unsteadiness, both of which are transmitted to the generator, the tower, and the active pitching mechanism, shortening the operating life due to fatigue loading.
In this project, we demonstrated a passive morphing blade concept capable of reducing load fluctuations without affecting the mean loads. The system allows both passive pitch adjustment to changes in the mean flow speed over the tidal period and mitigation of high-frequency fluctuations. This technology has been demonstrated through theoretical analysis, numerical simulation and experiments. The latter includes tests on a 1.2-m diameter turbine. Two different design concepts have been tested in the FloWave facility at the University of Edinburgh and in the recirculating channel at the Institute for Marine Engineering of the Italian National Research Council, respectively.
Experimental results show that the amplitude of power variations over a wide range of flow speeds is substantially decreased, while thrust variations with changes in freestream speed are essentially suppressed. The detrimental effect of yawed inflow is, in addition, almost entirely cancelled. The fluctuations in the root-bending moment, thrust and torque are consistently reduced over a broad range of tip-speed ratios.
Furthermore, we developed a theoretical and numerical framework that allows the design of passive pitch blades that can cancel either thrust or power fluctuations in specific flow conditions, as well as mitigate both types of fluctuations over a wide range of conditions. Specifically, we show that for any quasi-steady change in the relative flow speed and direction, there is a pitching axis that allows a chosen force component to be kept constant. High-frequency force fluctuations can also be substantially mitigated, and the extent of the mitigation depends on the inertia and friction in the system.
Overall, this project demonstrates the effectiveness of morphing blades for tidal turbines and presents a theoretical and numerical framework for the future development of this technology.
Exploitation Route Future development of this technology might include full-scale tests at sea.
Sectors Aerospace

Defence and Marine

Energy

URL https://voilab.eng.ed.ac.uk/publications#Energy
 
Description The world-leading tidal energy developer SIMEC Atlantis has developed a turbine blade design inspired by ours and filed a patent in 2023. We are aware that other tidal energy developers are considering adopting similar blade designs.
First Year Of Impact 2023
Sector Aerospace, Defence and Marine,Energy
Impact Types Economic

 
Description Michelin
Amount £96,000 (GBP)
Organisation Michelin 
Sector Private
Country France
Start 01/2023 
End 12/2023
 
Description CNR 
Organisation National Research Council
Country Italy 
Sector Public 
PI Contribution Dr Antonio Posa, Dr Riccardo Broglia and Dr Mario Felli, from CNR, have undertaken numerical and experimental research based on the conceptual ideas and methods derived from this project. We contributed to their work with complementary numerical and experimental work. This joint effort is likely to result in two or more high-impact joint papers in addition to those listed below.
Collaborator Contribution Broglia and Posa contributed to the project with high performance numerical simulations of a tidal turbine equipped with both fixed and passive pitch blades. Felli, who manages one of the large-scale water channels of CNR in Rome, contributed to the setting and run of proof of experiments of a 1.2-m-diameter turbine equipped with passive pitch blades in his facility. Tests were performed over 10 days in December 2022.
Impact Dai, W, Broglia, R & Viola, IM, 2022, 'Mitigation of Rotor Thrust Fluctuations through Passive Pitch,' Journal of Fluids and Structures, vol. 112, no. 103599, pp 23. https://doi.org/10.1016/j.jfluidstructs.2022.103599 Broglia, R, Posa, A & Viola, IM, 2022, 'Detached Eddy Simulations of isolated hydro-kinetic turbine: effect of tip speed ratio on the wake dynamics,' In the proceedings of the proceedings of the Global Conference on Naval Architecture and Ocean Engineering (G-NAOE 2022), Changwon, Republic of Korea, 06/11/2022 - 10/11/2022. Liu, Y, Gambuzza, S, Otomo, S, McCarthy, E, Young, A, Broglia, R & Viola, IM, 2022, 'Gust response and mitigation through passive pitching,' The 75th Annual American Physical Society Division of Fluid Dynamics Meting (APS-DFD), Indianapolis, IN, USA, 20/11/2022 - 22/11/2022. Liu, Y, Otomo, S, Gambuzza, S, Broglia, R, McCarthy, E, Young, A & Viola, IM, 2022, 'Gust mitigation through passive pitching,' The 14th European Fluid Mechanics Conference (EFMC14), Athens, Greece, 13/09/2022 - 16/09/2022.
Start Year 2021
 
Description Simec Atlantis Energy 
Organisation Simec Atlantis Energy
Country United Kingdom 
Sector Private 
PI Contribution SAE engineering team provided dedicated time to advice and test the proposed technology with their design tools. They provided confidential data on their turbines and contribute to the project's advisory board.
Collaborator Contribution The project delivered design ideas and data that is used by SAE for their own design.
Impact The collaboration has not resulted in direct outcomes (joint papers, joint patents, etc.) but has contributed to provide direction to the overall project and has ensured that the project remained industry relevant.
Start Year 2019
 
Title Apparatus and method for pitching a turbine blade 
Description Apparatus and method for pitching a turbine blade 
IP Reference PCT/GB2024/050216 
Protection Patent / Patent application
Year Protection Granted 2023
Licensed No
Impact Not yet
 
Title Turbine Blade 
Description This relates to a turbine blade, e.g. a turbine blade for use with a tidal turbine or a wind turbine, to a turbine comprising one or more of the turbine blades, to a trailing edge assembly for a turbine blade, and a kit of parts for a turbine blade. In particular, this relates to an adaptable camber turbine blade. 
IP Reference  
Protection Patent / Patent application
Year Protection Granted 2023
Licensed No
Impact We developed a new blade design structure that allows mitigation of unsteady loadings.
 
Title Piching blade steady 
Description This software allows to estimate the performance of a tidal turbine equipped with passively pitching blades. 
Type Of Technology Webtool/Application 
Year Produced 2023 
Open Source License? Yes  
Impact We aim to include results obtained with this code in a paper presenting the performance of a passive pitch turbine in varying inflow. 
URL https://git.ecdf.ed.ac.uk/sgambuzz/transTide
 
Title transTide 
Description transTide is a software that allows to estimate the loads generated by a tidal turbine under a turbulent, sheared inflow in the presence of yaw and surface waves. 
Type Of Technology Webtool/Application 
Year Produced 2021 
Open Source License? Yes  
Impact This has served as a basis for all papers that present low-order results on the turbine performance. 
URL https://git.ecdf.ed.ac.uk/sgambuzz/transTide
 
Description Morphing Blades Industrial Advisory Board Meeting and Public Meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A side event to the European Wind and Tidal Energy Conference was held on 4th September 2023 in Bilbao. The meeting aimed at showcasing progress on the Morphing Blades project and receiving feedback from practitioners and industry on the most suitable next steps of the project. The meeting was attended by about half of the conference attendees and had a duration of 90 minutes. The debate style of the meeting allowed gather significant feedback that informed the research plan for 2023 and 2024. The main outcome of the meeting was to provide confidence in the audience on the potential effectiveness of morphing blade technology.
Year(s) Of Engagement Activity 2023
URL https://ewtec.org/ewtec-2023/programme/
 
Description Open kick off meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact We held a kick-off meeting of the project in the form of a public side event to the European Wave and Tidal Energy Conference, in September 2021 at Plymouth.
Year(s) Of Engagement Activity 2021
URL https://ewtec.org/wp-content/uploads/2021/08/EWTEC-Summary-Schedule_1-combined.pdf