ALL-TTidal: Arrays of Long Life Turbines for Tidal

The project addresses the suitability of plastic bearings for use in arrays of tidal stream turbines. Numerical models will be developed and evaluated of a single device, calibrated against data from laboratory tests and field trials, and of arrays of devices, evaluated against data from laboratory tests. The approach draws directly on expertise of turbine array modelling at University of Manchester and of analysis of tidal turbine prototypes at Northeast Normal University. Unique datasets are provided by each partner from lab-scale array experiments at Manchester and field tests of a prototype at NENU. RANS BEMT and / or RANS Actuator Line models of a single turbine will be developed and the performance evaluated against prototype data from field trials. The mechanical and electrical power developed by each turbine is dependent on the variation of bearing friction with load. This will be quantified by NENU via laboratory tests and using data from field trials. The validity of RANS BEMT array models will be evaluated by comparison to detailed datasets for a fixed pitch turbine that are available to University of Manchester from earlier projects and which will be supplemented during this project. This will provide insight into the suitability of such RANS based models for turbine array simulations and into the influence of turbine operation on array yield. As such, interaction between energy extraction and resource will be neglected and the array configurations studied will be for row separations that are within the range of validity for RANS methods. Arrays of turbines with plastic bearings will be simulated to assess energy yield and inform assessment of the market, particularly in China, for the use of plastic bearings in tidal turbine applications.

In both the UK and China, ocean energy development is limited by uncertainty concerning the potential for cost reduction commercially acceptable rates. Technologies that reduce system cost are a key enabler in the development of a tidal stream market and realizing the potential contribution of this resource to the energy system. The application of novel plastic bearings and new passive variable-pitch turbine has been demonstrated to greatly increase the reliability of an offshore turbine. Understanding the contribution of this component type to array yield and standardization may reduce the system cost for tidal stream farms and would improve understanding of the potential market for high reliability tidal stream devices. Plastic bearings have been widely used in ocean engineering and new applications for such systems represent a larger market than traditional bearings in China. This project will provide important insight into the scale of this market and this is of particular relevance to the Hangzhou Jianghe Hydro-Electric Science & Technology Co. Ltd who partner with NENU on this project. .

The methods developed and the unique evaluation of RANS models for array applications builds on recent UK consortium projects and is closely aligned with the on-going EPSRC Marine Energy Challenge projects and the needs of the emerging tidal energy industry. The array simulations and evaluations proposed will provide insight into device-farm interactions and will improve understanding of approaches suitable for farm modeling. This work will also complement unsteady simulations of smaller arrays being conducted within parallel projects to improve understanding of the influence of ambient turbulence on turbine loading, including extreme loads, on wake generation and recovery. As such the methods and outcomes will aid ongoing efforts to establish coupled multi-scale models of turbine arrays. Further projects to progress this wider objective are under discussion, including with other UK and Chinese groups.