In the past twenty years, the use of wave energy systems has significantly increased, generally depending on the oscillating water column (OWC) concept. Wells turbine is one of the most efficient OWC technologies. This article provides an updated and a comprehensive account of the state of the art research on Wells turbine. Hence, it draws a roadmap for the contemporary challenges which may hinder future reliance on such systems in the renewable energy sector. In particular, the article is concerned with the research directions and methodologies which aim at enhancing the performance and efficiency of Wells turbine. The article also provides a thorough discussion of the use of computational fluid dynamics (CFD) for performance modeling and design optimization of Wells turbine. It is found that a numerical model using the CFD code can be employed successfully to calculate the performance characteristics of W-T as well as other experimental and analytical methods. The increase of research papers about CFD, especially in the last five years, indicates that there is a trend that considerably depends on the CFD method.

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Wells turbine for wave energy conversion: a review

Design of oscillating-water-column wave energy converters with an application to self-powered sensor buoys

Testing and control of a power take-off system for an oscillating-water-column wave energy converter

Improved design of a Wells turbine for higher operating range

The paper presents a detailed analysis of the dynamics and control of air turbines and electrical generators in oscillating-water-columns (OWCs). The aim is to explain the performance of an OWC device based on the physical behaviour of each system component. The Mutriku wave power plant was chosen as the test case. The power plant is a breakwater located in the Bay of Biscay, in Basque Country, Spain. The contributions of the work are: i) development of a hydrodynamic model of the power plant in the frequency domain; ii) implementation of a non-linear time-domain wave-to-wire model; iii) real-valued implementation of the Prony method for the computation of the wave-radiation force; iv) a detailed generator model based on experimental data to assess the influence of the generator efficiency on the power take-off performance; v) a critical performance comparison of the Wells and biradial turbines; vi) a sensitivity analysis of the control parameters of the turbine/generator set; and vii) an explanation of the comparative performance of both turbines based on statistical data. The turbine performance curves were taken from developers’ published experimental data. The results were obtained with a simplified model of the wave climate off the Mutriku test site comprising 14 sea states.

Dynamics and control of air turbines in oscillating-water-column wave energy converters: Analyses and case study

Air turbines are used to equip oscillating water column wave energy converters. In almost every case, self-rectifying turbines have been adopted which do not require non-return valves to rectify the reciprocating air flow induced by the water column oscillations. The most frequently used or proposed self-rectifying air turbines are the Wells turbine and the impulse turbine, both of axial-flow type. The fundamentals of the aerodynamic theory of axial-flow turbines are presented and then applied to the Wells turbine and the impulse turbine, including their variants. Information is given on methods of, and results from, air turbine model testing, as well as on self-rectifying air turbines that equipped or equip prototypes tested in the sea. The final part of the chapter is devoted to the analysis of turbine integration into OWC wave energy converter.

L.M.C. Gato

Papers

8.05 – Air Turbines