A 3D Unsteady Analysis of a Wells Turbine in a Sea-Wave Energy Conversion Device

Abstract

A Wells turbine designed for power generation in an innovative OWC (Oscillating Water Column) device for sea-wave energy conversion is investigated. This work aims to predict the turbine performance under a continuously variable reciprocating flow due to the action of the sea waves. When the amplitude of the oscillating flow reaches high values, stall occurs around the blades with a drop in the turbine performance. CFD simulation has been carried out aiming to provide an insight of flow behavior over the blades approaching these large amplitude flow conditions. Three test cases, preliminarily examined in order to assess the capability of the numerical methods, are presented and discussed: the first test-case concerns the 2D unsteady turbulent flow past a symmetrical airfoil undergoing oscillating pitching motion; the second test case concerns the 3D analysis of a high solidity Wells turbine in presence of different constant axial fluxes; the third test case concerns the 3D analysis of a high solidity Wells turbine in presence of an oscillating axial flux. Finally the flow past the low solidity Wells turbine rotor is simulated. The analysis has been performed by considering the flow to be unsteady, incompressible and viscous, while turbulence was modeled using the one-equation Spalart Allmaras model or the two-equations k-ω model.