Establishing the performance implications of employing lower cost methods for the manufacture of large scale tidal turbine rotors (EPICTidal)

Lead Research Organisation: Cranfield University
Department Name: School of Water, Energy and Environment

Abstract

One of the costlier items in current tidal turbine designs is the rotor blades. This project aims to assess the performance implications of the adoption of innovative, labour-saving, mechanized manufacturing processes for large diameter horizontal axis tidal turbines (>15 m) which could effect a substantial reduction in their cost. Current design practice involves consideration of the performance of tidal turbines in essentially quasi-steady operating conditions. The experience in the field, however, points to the fact that in energetic tidal locations the levels of in-stream turbulence are such as to impact negatively on their performance. The feasibility of combining lower cost manufacturing techniques for blades operating in turbulent tidal environments, with simpler designs which are tolerant of the transient operational conditions will be examined. The project seeks to establish what attendant modifications to an ideal datum design are involved in the streamlined construction and what are the performance implications of such modifications. The work will involve theoretical and experimental phases and will be carried out by a practised team of blade manufacturers and testing, design and analysis specialists

The team in Cranfield composed of Dr Joao Amaral-Teixeira and Dr Florent Trarieux will undertake the assessment of the performance of a selection of proposed rotors. This project will be undertaken in close collaboration with Nick Barlow, Founder and Managing Director of Southampton based leading composite blade manufacturer, Designcraft Ltd. The project is articulated around four phases of review of current manufacturing techniques, novel blade profile selection, numerical assessment using Blade Element Momentum models and state-of-the-art tank tests in three different tanks of increasing size, flow actuation type and turbulence levels: Cranfield Towing Tank, Haslar Towing Tank and Boulogne-sur-mer Circulation Channel.

Planned Impact

This research will be very much relevant to UK Tidal Energy Industry and particularly for tidal developers considering large arrays with rotors > 15 m diameter.

Publications

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Description Tidal Turbine blades represent a sizeable purchasing item by cost when developing one of these devices. The constructional methodologies traditionally employed are labour and material intensive and are therefore directly associated with the cost of these devices. The project was performed in partnership with a blade manufacturer whose experience is directly relevant to the project. This research programme has enabled the company as well as the academic institution to acquire experience in the design for manufacture of tidal turbine blades. A number of two, three and five bladed turbines have been designed and built by the industrial partner and subsequently tested in three water tanks, two of which were towing tanks and the third a circulation tank. More than 1000 tests were performed and these enabled relating the blade constructional approach with the attending performance implications. Utility scale wind turbines are constructed with invariably three blades per rotor on account of turbine performance, dynamic stability and blade manufacturing cost. This latter item impacts greatly on the costs of tidal turbine development and is one of the reasons most turbines used in tidal applications employ two blades. There is however a considerable difference between the environment in which these two turbine types operate in. Although turbulence is also present in wind, as in tidal currents, on account of the density of the water, the unsteady forces generated by the turbulence in the sea are vastly in excess of what is experienced by an equivalent power wind turbine. For this reason, survivability in intense turbulent blade loading conditions, leading to the premature fatigue of a number of turbine components, including those which make up the drive train, is a primary consideration for tidal turbine designers. The project findings suggest that multi bladed turbines, constructionally simple to produce, with slender flexible blades may offer the solution which combines turbulence tolerance, manufacturing cost and power conversion efficiency.
Exploitation Route Both Cranfield University and Designcraft Ltd benefited directly from this program and indirectly their clients and wider society. Both organisations in different ways have been associated for some years with tidal power generation supporting the development of this renewable resource into a commercially viable enterprise. The premise of the project proposal was that it is possible to reduce the capital cost of rotor construction through additional mechanisation of the build process. The focus of the project was therefore to understand how these more basic geometries will perform by comparison with a more complex, and hence costlier to produce, turbine blade. The project enabled the comparison of a range of designs which can be related back to their full scale constructional cost enabling the rating of the performance against design features. For the two organisations the findings and experience acquired as part of this project will be directly incident in the design solutions to be proposed for future tidal turbine applications.
Sectors Energy
 
Description The project was run in close collaboration with Designcraft Ltd who have practical experience in the manufacturing of tidal turbine rotors. The company is aware of the large investment required for the manufacturing of the blades is proposing a reduction these costs through the adoption of a construction technique requiring less direct manpower involvement in the replacement of the laborious aspects of the construction with more mechanised procedures. However the switching between the two approaches requires the adoption of designs which have a number of simple geometric features which are more amenable to mechanisation. The extensive number of designs tested in the three water tanks enabled the evaluation of the relative performance which is a function of the design parameters of the tested turbine models. The analysis of these tests has enabled the industrial partner to relate their proposed cost-reduction manufacturing solutions to the attending turbine performance implications for a variety of designs and configurations. Regarding communication to a wider audience the departure from Cranfield University of Dr Florent Trarieux, who was the academic who oversaw the experimental campaign, at the very end of the project, has meant that the publication plans have not been acted on within the immediate termination of the project as initially intended. Dr Trarieux remains committed however to publishing this work in the near future.
First Year Of Impact 2018
Sector Energy
Impact Types Societal,Economic