Tidal Stream Turbines - Renewable Energy from the Tides

 

Tidal Stream Turbines - Renewable Energy from the Tides

For more information, visit https://www.airshaper.com or email info@airshaper.com ---------------------------------------------------------------------------------------- Also check out Fluid Mechanics 101: https://www.youtube.com/channel/UCcqQi9LT0ETkRoUu8eYaEkg On Aidan's channel, you can also find the uncut, full length video of this interview: https://youtu.be/Ntl15C2KXCQ ---------------------------------------------------------------------------------------- For this video, we interviewed Aidan Wimshurst, who did his PhD at Oxford University (United Kingdom) on Tital Power Generation. Concept Tidal currents originate because of the tides: as water levels change, water flows from one area to another. When the water needs to fit through a narrow channel or move around certain coastlines, flow speeds can be quite high. These streams are very predictable, which makes it much easier to integrate the energy they produce into the grid. The general idea is to take a typical 3-bladed wind turbine and put it under water. But there are a number of key differences to wind turbines that make tidal turbines unique. Wing tip vortex On an airplane, the air at the high pressure location below the wing wants to move to the low pressure location at the top of the wing via the side (the wing tip). This creates a curling motion called wing tip vortex. On a turbine, this vortex also exists but it leaves a spiral trace instead of a linear one. And this increased vorticity & turbulence can impact turbines further downstream. It also represents efficiency losses for the turbine itself, which is why some (wind turbine) blades are equipped with winglets. Cavitation If pressure is reduced below the vapor pressure, you will start getting bubbles. When these implode, they can cause serious damage to the blades, structure, and so on. The risk of cavitation is reduced when the hydrostatic pressure is high, close to the sea bed. But close to the surface, this hydrostatic pressure is much lower, increasing the risk of cavitation. So the risk of cavitation varies along a single revolution. Farm layouts For a given plot of land, the goal is to maximize energy and thus put as many turbines as possible in place. But if you put them too close to each other, the turbulent wake of one turbine will lower the efficiency and lifetime expectancy of other turbines, so there is an optimum to be found. With tidal energy, the orientation of the flow is always the same, only changing direction between tides. So these are typically placed in an array. The flow around a turbine is accelerated, meaning that a turbine placed in this accelerated flow will yield more power, ánd the original turbine will also perform better. This is called constructive interference. This will be analyzed in the MeyGen project. Size trends Compared to wind turbines, the constraints are different for tidal energy. The water depth is typically between 20 and 50 meter, so that limits the rotor size. Also, the velocity shear (difference between the velocity at the bottom and free water surface) poses strong bending loads on the rotor. Suitable sites Tidal energy will never be able to provide the full energy demand of a country, but it can provide a valuable contribution. And it's also very useful for remote sites, which are typically islands, as they have difficult access to other sources of energy.

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Code contributions by

  • KU Leuven
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  • Linkoping University