Wake hydrodynamics downstream from a horizontal axis turbine under current flow and waves

Jordan, Laura-Beth

March 2018

Thesis or dissertation

© 2018 Laura-Beth Jordan. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Due to concerns over the potential impacts of climate change on the environment, there is a growing interest in developing renewable forms of energy. Tidal streams are a potential source of renewable energy that can be harnessed for electricity generation using tidal stream turbines. However, due to the technology being a relatively new development, with limited testing and commercial applications, the flow dynamics and environmental impact of such devices is still poorly understood.

This research investigates the flow dynamics downstream from a horizontal axis tidal stream turbine device using a physical modelling experiment in the Total Environment Simulator laboratory flume, using a channel which measured 11m long, 1.6m wide and 0.6m deep. Detailed flow measurements were collected using a two-camera submersible Particle Image Velocimetry (PIV) system to quantify the three-dimensional flow velocities and turbulence downstream from the model tidal turbine device. A wide range of rotor positions and flow conditions were tested, including current flow and combined wave-current flows. The data collected will be used to validate numerical models developed by project partners, which will assist with developing full-scale operational tidal stream turbines.

The presence of the tidal stream turbine within the channel had a significant impact on the flow downstream. A significant velocity deficit was observed in the wake of the turbine. This was particularly skewed, owing to the turbine rotation, to the right hand side of the centreline, where the deficit was greater than the left hand side. Subjecting the turbine to wave-current flow reduced this deficit considerably, with the shortest wake length occurring under the troughs of waves. Positioning the turbine closer to the bed resulted in a substantial increase in shear stress, with vertical and horizontal asymmetry observed in the wake of the turbine and horizontal asymmetry observed in the resulting scour below the turbine.

The work outlines the impact of these variables on seafloor scour and integrity, and highlights and discusses the optimisation of turbine efficiency with minimal wake and seafloor scour impacts.

School of Environmental Sciences, The University of Hull
McLelland, S. J.(Stuart J.); Parsons, Daniel R.
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