BLOG – SELKIE TOOL SERIES: Computational Fluid Dynamics tool for tidal arrays

BLOG – SELKIE TOOL SERIES: Computational Fluid Dynamics tool for tidal arrays

As part of the Selkie Project, a computationally efficient tool for simulating the performance and wake characteristics of horizontal axis tidal turbine arrays is being developed. The aim of this research is to provide an open access, clearly documented tool for the marine renewable energy industry and the research community to facilitate their individual device design as well as array layout optimisation for energy output maximisation.

Through the application of this tool, users will be able to numerically test their device and array designs in both controlled and realistic environments, such as laboratory conditions and potential sites with complex bathymetry and realistic tidal conditions. This tool will also allow users to apply varying pitch or stall control conditions on individual devices in an array to reflect the different conditions each of the turbines may operate in. The immediate outputs of this tool include aspects of performance of the devices and detailed flow dynamics in the upstream and downstream areas of the turbines, providing users with necessary information to analyse and understand the responses of their devices to their surrounding environment.

The software implementation uses the Generalised Actuator Disk Computational Fluid Dynamics (GAD-CFD) model1. It includes modifications to the angle of attack to improve the capture of tip loss effects by conforming to the constraints outlined in Prandtl’s lifting line theory, and a lift distribution method which captures the geometric aspects of the foil, i.e. twist, chord and profile. The model also allows for the use of foil data at a range of Reynolds numbers. The GAD-CFD model presents a significant improvement over other similar techniques for predicting power and thrust, and requires significantly less computational effort than fully resolving the geometry of turbines. This then allows the model to be applied to turbine array simulations at a reasonable computational cost. 

An example of the application of GAD-CFD model to analyse two different array layouts: modified rotor array layout (top left photo) and regular array layout (top right photo). Power outputs for the two layouts are shown in the bottom graph.

Alongside development, the reliability of the model has been tested through a comparison of its predictions with high fidelity laboratory measurements from the IFREMER flume tank for single turbine tests, and the University of Edinburgh circular Flowave tank for array tests. During the course of the Selkie Project, the aim is to test the performance of the model for simulating full-scale turbines in a controlled environment. This will then be expanded to consider coastal waters with large exploitation potential. The targeted release date of the tool is Summer 2021.

A workshop, aimed at demonstrating progress, and enabling professionals and researchers in the marine renewable energy sector to influence the development of this tool will be held by the Selkie team in cooperation with Marine Energy Wales in the coming months. Please follow the Selkie project (@SelkieProject) on Twitter for future updates and sign up to the Selkie mailing list at the bottom of this web page. You are also very welcome to contact xiaorong.li@swansea.ac.uk for details.

1“An enhanced disk averaged CFD model for the simulation of horizontal axis tidal turbines” Renewable Energy 101 (2017) 67–81.