Understanding tidal turbines

Our MSc students are about to start their third, and final, term. This is a big one. Over the next few months they have to do an independent research project on an energy topic of their choosing. Napat Tongmark, one of our students from Thailand, is focussing on marine turbines, one of the core technologies needed to harness the power of the tides.

Currently the world is looking to try to mitigate climate change and reduce carbon emissions. Renewable energy has taken centre stage in this debate particularly since the Paris Agreement. One area that has garnered a lot of interest is tidal energy. This is a little used technology that could potentially be the kind of low-impact, sustainable energy development that is needed.

Artist’s impression of the proposed visitor centre at the Tidal Lagoon Swansea Bay.
Artist’s impression of the proposed visitor centre at the Tidal Lagoon Swansea Bay.

In the hope of providing more understanding in this field, I have decided to research these tidal technologies. The aim with my project, Loading of Tidal Turbine Blades, is to provide an insight and help improve design of turbine arrays. The project is being supervised by Dr.Johannes Spinneken and Georgios Deskos, both in the Department of Civil and Environmental Engineering.

I will be investigating a single turbine device in a harsh marine environment through complex computer simulations. The main purpose is to gain more understanding of the ocean environment and its interactions with the turbine. This should help future machines to extract more power and reduce the “wake effect” behind a turbine.

The work will actually build on my experience as an undergraduate when I used mechanical analysis software to design and manufacture a prosthetic foot. The prosthetic proved to be a significant improvement on commercial products and showed me the power of computational analysis in engineering projects. I will use the project to help me broaden my knowledge and experience in computational programming and analysis and gain more understanding of its use with fluids.

moon-67903Tidal energy is subtly different from other energy sources as it is a result of planetary motion, interactions between the Earth, moon and sun, while the others are basically driven by energy from the sun. The planetary movements are calculable making the tidal energy highly predictable among other renewables. Through good management in a tidal energy system, you can even reduce the need for secondary energy storage.

Currently only a few hundred megawatts of tidal power have been harnessed with more than a thousand times that untapped. Difficulties arise when an attempt is made to invest in and implement tidal turbine technology. The technology is still mainly at a research and development level and a lot of this is still looking at how to predict flow behaviours and indicate how much energy we can get from tides. Despite the lack of research and the high upfront costs there are many projects planned but they need to know what works and what doesn’t to be successful.

Getting energy from the tides is easy in theory. You put a turbine in the water and as the tide goes in and out it turns and you get energy. In practice it’s subtly different. To get the most out of tidal energy in a water channel you need loads of them. However the first row of the turbines extract tidal current energy and then disturb the water flow. This disturbance in the water behind a turbine is called ‘wake’ and may cause adverse effects in downstream. Understanding of wake characteristics behind a single tidal turbine is vital, yet, there is a limited number of studies in this area.

Sample picture of an expected result from similar research, downstream velocity profile (Edmunds et al., 2014)
Sample picture of an expected result from similar research, downstream velocity profile (Edmunds et al., 2014)

My project will use computer simulations to examine wake responses from under different conditions. This is a lot easier than using costly, real world, experiments that can only look at a limited range of conditions.

I will be using a new simulation technique, vortex filament method, which has not yet been fully applied in this field of study. I expect to be able to obtain dimensions of wake structure that were unclear in previous studies, velocity profiles behind a tidal turbine and mixing behaviours in the wake region. All my results will then be compared with previous studies and hopefully provide more insight in the turbine array design. This research could become a crucial part of global sustainability development in the area of tidal energy.

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