A modified Wells turbine for wave energy conversion

Oscillating-water-column wave energy converters and air turbines: A review

Abstract: The ocean waves are an important renewable energy resource that, if extensively exploited, may contribute significantly to the electrical energy supply of countries with coasts facing the sea. A wide variety of technologies has been proposed, studied, and in some cases tested at full size in real ocean conditions. Oscillating-water-column (OWC) devices, of fixed structure or floating, are an important class of wave energy devices. A large part of wave energy converter prototypes deployed so far into the sea are of OWC type. In an OWC, there is a fixed or floating hollow structure, open to the sea below the water surface, that traps air above the inner free-surface. Wave action alternately compresses and decompresses the trapped air which is forced to flow through a turbine coupled to a generator. The paper presents a comprehensive review of OWC technologies and air turbines. This is followed by a survey of theoretical, numerical and experimental modelling techniques of OWC converters. Reactive phase control and phase control by latching are important issues that are addressed, together with turbine rotational speed control.

Comprehensive Renewable Energy

Abstract: "Comprehensive Renewable Energy" is the only multi-volume reference work of its type at a time when renewable energy sources are seen increasingly as realistic alternatives to fossil fuels. As the majority of information published for the target audience is currently available via a wide range of journals, seeking relevant information (be that experimental, theoretical, and computational aspects of either a fundamental or applied nature) can be a time-consuming and complicated process. "Comprehensive Renewable Energy" is arranged according to the most important themes in the field (photovoltaic technology; wind energy technology; fuel cells and hydrogen technology; biomass and biofuels production; hydropower applications; solar thermal systems: components and applications; geothermal energy; ocean energy), and as such users can feel confident that they will find all the relevant information in one place, with helpful cross-referencing between and within all the subject areas, to broaden their understanding and deepen their knowledge. It is an invaluable resource for teaching as well as in research. Available online via SciVerse ScienceDirect and in print. Editor-in Chief, Professor Ali Sayigh (Director General of WREN (World Renewable Energy Network) and Congress Chairman of WREC (World Renewable Energy Congress, UK) has assembled an impressive, world-class team of Volume Editors and Contributing Authors. Each chapter has been painstakingly reviewed and checked for consistent high quality. The result is an authoritative overview which ties the literature together and provides the user with a reliable background information and citation resource. The field of renewable energy counts several journals that are directly and indirectly concerned with the field. There is no reference work that encompasses the entire field and unites the different areas of research through deep foundational reviews. "Comprehensive Renewable Energy" fills this vacuum, and can be considered the definitive work for this subject area. It will help users apply context to the diverse journal literature offering and aid them in identifying areas for further research. Research into renewable energy is spread across a number of different disciplines and subject areas. These areas do not always share a unique identifying factor or subject themselves to clear and concise definitions. This work unites the different areas of research and allows users, regardless of their background, to navigate through the most essential concepts with ease, saving them time and vastly improving their understanding. There are more than 1000 references from books, journals and the internet within the eight volumes. It is full of color charts, illustrations and photographs of real projects and research results from around the world. The only reference work available that encompasses the entire field of renewable energy and unites the different areas of research through deep foundational reviews. Allows readers, regardless of their background, to navigate through the most essential concepts with ease, saving them time and vastly improving their understanding.

Multi-objective optimization of the airfoil shape of Wells turbine used for wave energy conversion

Abstract: Wells turbine is one of the technical systems allowing an efficient use of the power contained in oceans’ and seas’ waves with a relatively low investment level. It converts the pneumatic power of the air stream induced by an Oscillating Water Column into mechanical energy. The standard Wells turbines show several well-known disadvantages: low tangential force, leading to low power output from the turbine; high undesired axial force; usually a low aerodynamic efficiency and a limited range of operation due to stall. In the present work an optimization process is employed in order to increase the tangential force induced by a monoplane Wells turbine using symmetric airfoil blades. The automatic optimization procedure is carried out by coupling an in-house optimization library (OPAL (OPtimization ALgorithms)) with an industrial CFD (Computational Fluid Dynamics) code (ANSYS-Fluent). This multi-objective optimization relying on Evolutionary Algorithms takes into account both tangential force coefficient and turbine efficiency. Detailed comparisons are finally presented between the optimal design and the classical Wells turbine using symmetric airfoils, demonstrating the superiority of the proposed solution. The optimization of the airfoil shape leads to a considerably increased power output (average relative gain of +11.3%) and simultaneously to an increase of efficiency (+1%) throughout the full operating range.

Wells turbine for wave energy conversion: a review

Abstract: 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.

High performance ocean energy harvesting turbine design–A new casing treatment scheme

Abstract: Delaying a stall improves the performance of any turbomachinery system. TC (tip clearance), which is used in a bi-directional flow Wells turbine of an ocean wave energy device, changes the flow pattern on the turbine blade suction surface, while changing or modifying the TC zone can help obtaining a delayed stall. In the present work, a new tip grooving scheme is introduced and the performance is compared for different tip groove depths and TCs of a Wells turbine. The performance is defined in terms of wider operating range or stall delay, power production and efficiency. The problem was solved by a numerical analysis technique. A multi-block meshing scheme was employed to generate structured and hexahedral elements in the computational domain and the flow was solved in ANSYS CFX® v14.5 by solving Reynolds-averaged Navier Stokes equations. It was found that the grooves improve the turbine operating range and power production as compared to those of the turbine without a groove. The groove depth of 3% of the chord length produced highest power and widest operating range. Using the circumferential groove, 26% increase in turbine power output for a particular operating point is achieved.

The wells air turbine for wave energy conversion

Abstract: The wave energy devices currently in operation in the United Kingdom and India and those that are to be built in Europe are based on the principle of the oscillating water-air column. In these devices the pneumatic energy of the oscillating air column is converted to mechanical energy of rotation by a Wells turbine. A monoplane (single plane) Wells turbine can absorb only a certain maximum pneumatic pressure amplitude due to tip speed limitations. For wave energy devices which produce large amplitudes of pneumatic pressure a biplane Wells turbine with or without guide vanes can be used. The prediction methods currently available and parameters controlling the aerodynamic performance of the Wells turbines are reviewed. Some novel techniques to improve the performance of Wells turbine are suggested.

Analysis of Wells turbine design parameters by numerical simulation of the OWC performance

Abstract: This paper investigates by numerical simulation the influence of the Wells turbine aerodynamic design on the overall plant performance, as affected by the turbine peak efficiency and the range of flow rates within which the turbine can operate efficiently. The problem of matching the turbine to an oscillating water column (OWC) is illustrated by taking the wave climate and the OWC of the Azores power converter. The study was performed using a time-domain mathematical model based on linear water wave theory and on model experiments in a wave tank. Results are presented of numerical simulations considering several aerodynamic designs of the Wells turbine, with and without guide vanes, and with the use of a bypass pressure-relief valve.

The Offshore Floating Type Wave Power Device ”Mighty Whale” Open Sea TestsPerformance of The Prototype –

Abstract: Mighty Whale is a floating wave power device based on the Oscillating Water Column (OWC) principle. It converts wave energy into electric energy, and produces a relatively calm sea area behind. The open sea tests were begun in September 1998 in Gokasho Bay, Nansei Town, Mie Prefecture. Measurements collected since then include performance data in typhoon seasons. This paper presents the measurements of wave energy absorption, floating body motion, and wave height dissipation. It is expected that these results will be useful in the design of offshore wave power devices in the future.

The Offshore Floating Type Wave Power Device "Mighty Whale": Open Sea Tests

Abstract: JAMSTEC completed the construction of the prototype device Mighty Whale by May 1998 for open sea tests to investigate practical use of wave energy. Following construction, the prototype was towed to the test location near the mouth of Gokasho Bay in Mie Prefecture. The open sea tests were begun in September 1998, after final positioning and mooring operations were completed. The tests are expected to continue for approximately 2 years. This paper presents an overview of the open sea tests, and summarizes the characteristics of power generation based on the results so far.

Study On an Impulse Turbine For Wave Energy Conversion

Abstract: The objective of this paper is to clarify the performance of impulse turbine with fixed guide vanes and to compare it with that of Wells turbine with guide vanes. As a result, a suitable choice of the design factors for the impulse turbine was shown for the inlet angle of rotor blade and the shape of guide vane. Furthermore, it was found that the running and starting characteristics of the impulse turbine were superior to those of the Wells turbine under irregular wave condition.