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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