Study on the performance of helical savonius rotor for wave energy conversion

Abstract

This paper presents a numerical study of the savonius type direct drive turbine in typical chamber geometry of an oscillating water column chamber (OWC) for wave energy conversion. The paper deals with a numerical modeling devoted to predict the turbine efficiency in the components of an oscillating water column (OWC) system used for the wave energy capture. In the present paper, the flow behavior is modeled by using the commercial code ANSYS CFX. Three numerical flow models have been elaborated and tested independently in the geometries of a water chamber with a conventional three bladed savonius type wave turbine and a three bladed helical savonius type turbine. Conventional three bladed savonius rotors have high coefficient of static torque at certain rotor angles. In order to increase the efficiency of the system a helical savonius rotor with a twist of certain proposed degree is introduced. Constant periodic wave flow calculations were performed to investigate the flow distribution at the turbines inlet section, as well as the properties of the savonius type turbine. The flow is assumed to be two‐dimensional (2D), viscous, turbulent and unsteady. The commercial CFD code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the hexahedral mesh and the moving mesh techniques in areas of moving surfaces. Turbulence is modeled with the k‐e model. The obtained results indicate that the developed models are well suitable to analyze the water flows both in the chamber and in the turbine. For the turbine, the numerical results of pressure and torque were compared with each other.