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Optimisation of a vertical axis tidal turbine and testing of a prototype in an unblocked environment

Priegue Molinos, Luis 2017. Optimisation of a vertical axis tidal turbine and testing of a prototype in an unblocked environment. PhD Thesis, Cardiff University.
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Vertical Axis Tidal Turbines (VATTs) have become the subject of increased interest in recent decades, but the development of this type of hydrokinetic turbine has faced several challenges that have not yet been overcome. The influence of rotor parameters on turbine performance is one of these challenges. No axiom can be found in the literature about the effect of these parameters on the turbine behaviour, and sometimes research projects even show contradictory results. As a consequence, parameters that define turbine rotors may differ substantially from each other but have performed similarly in terms of efficiency. In relation to this matter, experimental modelling has been carried out in the School of Engineering facility at Cardiff University. Using small-scale set-ups, experimental testing provided useful and reliable information that shed light into these design uncertainties. Blade roughness has been found to have a great impact on the turbine behaviour, and the influence of this parameter has been tested and analysed in depth in a subsequent chapter of the thesis. Apart from the parametric analysis, a mechanical and an electrical system were utilised for the turbine set up. Thanks to these different systems of energy conversion, it was possible to compare the extracted power and to evaluate their inherent losses. Electricity was generated from the electrical approach, which was very useful in order to accurately evaluate the turbine efficiency. Taking into account the results coming from physical testing, an optimised prototype of a VATT was designed and manufactured; estimated to be a 1:15 scale device. Not just the rotor but the whole super structure was built, in order to analyse both the efficiency and the performance of the rotor, as well as the 1 structural response of the entire device. Performing experimental testing without removing the effect that a blocked channel provides to the turbine rotation is no trivial issue, and intermediate scale tests will become a fundamental step for recognition of the technology. Aiming to achieve a reliable source of information, the manufactured tidal turbine prototype has been tested in a water sports centre (White Water Rafting Centre, Cardiff). There is a clear lack of information in the literature about testing tidal turbines on an intermediate scale, and the chance to test a tidal turbine is a very valuable opportunity. The experiments were accomplished in a very similar environment to a real tidal stream, but with the related advantages of complete control over the turbine deployment. Thus, these experiments are considered to provide very useful data for scientific knowledge and also the tidal stream energy sector. Finally, the study of the hydrodynamic turbine wake in small scale was carried out. Not only velocity measurements were collected at the turbine operating point, but also water elevations upstream and downstream were measured by using depth gauges based on water conductivity. At the time of writing and to the best of the authors’ knowledge, not many research articles have studied the wake characteristics of vertical axis tidal stream turbines, and none have used this equipment. The quality of the data is deemed to be excellent and the following process of the information described perfectly the near and far wake. This could be extremely useful for a future scale-up of the turbine, and the development of an array. 2

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Vertical axis tidal turbine; experimental testing; wake characteristics; tidal turbine performance; parametric analysis.
Date of First Compliant Deposit: 9 May 2017
Last Modified: 24 Aug 2022 09:02

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