This paper describes the present status of the art on air turbines, which could be used for wave energy conversion. The air turbines included in the paper are as follows: Wells type turbines, impulse turbines, radial turbines, cross-flow turbine, and Savonius turbine. The overall performances of the turbines under irregular wave conditions, which typically occur in the sea, have been compared by numerical simulation and sea trial. As a result, under irregular wave conditions it is found that the running and starting characteristics of the impulse type turbines could be superior to those of the Wells turbine. Moreover, as the current challenge on turbine technology, the authors explain a twin-impulse turbine topology for wave energy conversion.

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Air Turbines for Wave Energy Conversion

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

The present invention is used as power for wave energy of the ocean, and relates to the use of the energy of the high-pressure sea water, the apparatus 10, which was generally converted to a water pressure of greater than greater than 800psi and preferably 100psi. Sea water of the high pressure generated by the device 10 may be transported through the pipe to shore for any suitable purpose. The device 10 includes a pump 13 operatively connected to the support to hang in the water body (1), the float 12, and the float (12). And the pump 13 comprises a piston 61 extending between the take entrance 47, the take-out chamber (49) and the take entrance 47 and the take-out chamber (49). The piston 61 includes a tube 63 having a flow passage 102 extending between the take entrance 47 and the take-out chamber (49). The piston 61 and the take-out chamber (49) are cooperating to form the expansion and the pumping chamber (100) to receive a contraction in accordance with the reciprocating motion of the piston. The piston 61 is operatively connected to the float (12) to be driven by upward movement of the float. The pump may be to process the water to pass by using the electrolytic process, to accept from a linear electric generator employed in the pump. Seawater, wave energy, buoyancy, pumps, water treatment

Wave Energy Conversion

Passive flow control for aerodynamic performance enhancement of airfoil with its application in Wells turbine – Under oscillating flow condition

Numerical analysis of a unidirectional axial turbine for twin turbine configuration

A twin unidirectional impulse turbine has been proposed in order to enhance the performance of wave energy plant. This turbine system uses two unidirectional impulse turbines and their flow direction is different from each other. However, the turbine characteristics have not been clarified to date. The performances of a unidirectional impulse turbine under steady flow conditions were investigated experimentally by using a wind tunnel with large piston/cylinder in this study. Then, efficiency of the twin impulse turbine have been estimated by a quasi-steady analysis using experimental results.

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A twin unidirectional impulse turbine for wave energy conversion

Wells turbine has inherent disadvantages in comparison with conventional turbines: relative low efficiency at high flow coefficient and poor starting characteristics. To solve these problems, the authors propose Wells turbine with booster turbine for wave energy conversion, in order to improve the performance in this study. This turbine consists of three parts: a large Wells turbine, a small impulse turbine with fixed guide vanes for oscillating airflow, and a generator. It was conjectured that, by coupling the two axial flow turbines together, pneumatic energy from oscillating airflow is captured by Wells turbine at low flow coefficient and that the impulse turbine gets the energy at high flow coefficient. As the first step of this study on the proposed turbine topology, the performance of turbines under steady flow conditions has been investigated experimentally by model testings. Furthermore, we estimate mean efficiency of the turbine by quasi-steady analysis.

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Wells Turbine for Wave Energy Conversion —Improvement of the Performance by Means of Impulse Turbine for Bi-Directional Flow

As a system using a conventional unidirectional air turbine in oscillating water column (OWC) based on a wave energy plant, a twin unidirectional impulse turbine topology has been suggested in previous studies. However, the average efficiency of the suggested twin turbine is considerably lower than that of a conventional unidirectional turbine in this topology because reciprocating air flow can’t be rectified adequately by a unidirectional turbine. In order to improve the efficiency, using fluidic diode is discussed. In this study, two different fluidic diodes were discussed by computational fluid dynamics (CFD) and a wind tunnel test. Further, its usefulness is discussed from a view point of the turbine efficiency. The fluidic diode was shown to improve rectification of the topology. However, it needs more improvement in regards to its energy loss in order to enhance the turbine efficiency.

/pdf/a-twin-unidirectional-impulse-turbine-for-wave-energy-bye6zkaz10.pdf

A Twin Unidirectional Impulse Turbine for Wave Energy Conversion—Effect of Fluidic Diode on the Performance

A twin unidirectional impulse turbine has been proposed in order to enhance the performance of wave energy plant. This turbine system uses two unidirectional impulse turbines and their flow direction is different each other. However, the effect of guide vane solidity on the turbine characteristics has not been clarified to date. The performances of a unidirectional impulse turbine under steady flow conditions were investigated experimentally by using a wind tunnel with large piston/cylinder in this study. Then, mean efficiency of the twin impulse turbine in bidirectional airflow has been estimated by a quasi-steady analysis using experimental results in order to investigate the effect of guide vane solidity on the performance.

A Twin Unidirectional Impulse Turbine for Wave Energy Conversion —Effect of Guide Vane Solidity on the Performance

Wells turbine has long been used as an energy converter for wave energy conversion because of its simple structure. In order to alleviate the stall problem of this turbine, the authors have proposed a Wells turbine with booster for wave energy conversion. This unique power take-off consists of the Wells turbine for main turbine and a impulse turbine for booster. In the present, the wind-tunnel tests are conducted to investigate the turbine characteristics under steady flow conditions and the effect of rotational speed ratio on the turbine performance is estimated by the quasi-steady numerical analysis. As a result, the efficiency of Wells turbine with booster which has small diameter ratio DW/Di depends strongly on the rotational speed ratio Ni/NW.

Akiyasu Takami

Papers

A twin unidirectional impulse turbine for wave energy conversion

Wells Turbine for Wave Energy Conversion —Improvement of the Performance by Means of Impulse Turbine for Bi-Directional Flow

A Twin Unidirectional Impulse Turbine for Wave Energy Conversion—Effect of Fluidic Diode on the Performance

A Twin Unidirectional Impulse Turbine for Wave Energy Conversion —Effect of Guide Vane Solidity on the Performance

917 Wells Turbine with Booster : Effect of Rotational Speed Ratio on the Performance