The objective of this paper is to report the effects of Reynolds number and hub-to-tip ratio on the performance of the impulse turbine for wave energy conversion. The turbine was investigated experimentally under steady and sinusoidally oscillating flow conditions by model testing. As a result, it was found that the critical value of Reynolds number and the optimum hub-to-tip ratio are approximately 4.0×104 and 0.7, respectively. Furthermore, their effect on starting characteristics have been clarified.

The aim of this study is to clarify the effect of rotor blade profile on the performance of the Wells turbine operated at high Reynolds number. In the study, four kinds of blade profile were selected with regard to the blade profile of the Wells turbine. The types of blade profile are as follows: NACA0020, NACA0015, CA9, and HSIM 15-262123-1576. In order to determine the optimum rotor blade profile of the turbine, experimental investigations have been performed for two solidities by model testing and numerical simulation. As a result, it has been concluded that a suitable choice, namely the preferable rotor geometry, is the blade profile of NACA0015. Furthermore, it has been found that the critical Reynolds number of the turbine is around 4×10⁵.

For the practical application of a fixed oscillating water column (OWC)-type wave energy converter, it is necessary to develop a design method which can consider the characteristics of incident wave motion, the motion of the internal free surface affected in the structure such as a partly submerged wall, the fluctuation of air pressure in an air chamber, and the rotation of the air turbine. On the other hand, the impulse turbine as the secondary conversion device in the OWC unit is expected to achieve high efficiency. In this paper, firstly, the steady air flow tests for a single-impulse turbine were conducted to grasp the characteristics of the turbine without the effect of water waves. Secondly, the 2-dimensional wave tank tests in regular waves for the performance evaluation of the fixed OWC-type wave energy converter with the same impulse turbine were conducted to obtain the data needed to make this design method. As the results, the effects of the air chamber length and the guide vane’s setting angle on the primary and secondary conversion efficiencies are clarified experimentally.

The present study reported of the numerical investigation of a high-speed wet steam flow through an asymmetric nozzle. The spontaneous non-equilibrium homogeneous condensation of wet steam was numerically modeled based on the classical nucleation theory and droplet growth rate equation combined with the field conservations within the computational fluid dynamics (CFD) code of ANSYS Fluent 13.0. The equations describing droplet formations and interphase change were solved sequentially after solving the main flow conservation equations. The calculations were carried out assuming the flow two-dimensional, compressible, turbulent, and viscous. The SST k-ω model was used for modeling the turbulence within an unstructured mesh solver. The validation of numerical model was accomplished, and the results showed a good agreement between the numerical simulation and experimental data. The effect of spontaneous non-equilibrium condensation on the jet and shock structures was revealed, and the condensation shown a great influence on the jet structure.

Bi-directional airflow is generated in the wave energy plant with oscillating water column (OWC). Turbines for bi-directional airflow have been used in such devices, and they rotates in the same direction. Some turbines for bi-directional airflow were proposed, and their performance were investigated by wind tunnel tests and CFD analyses. Typical turbines have some inherent disadvantages such as severe stall and low efficiency. Therefore, the authors proposed two unique turbines for bi-directional flow: Wells turbine with booster and counter-rotating impulse turbine. Extensive numerical works were conducted to perform a comparative study between the conventional and proposed turbines.