A 3D numerical investigation of the influence of the geometrical parameters of an I-beam attenuator OWC on its performance at the resonance period

Abstract

The oscillating water column (OWC) is the oldest and most reliable concept for wave energy conversion. This paper investigates the hydrodynamic performance of one chamber of an I-Beam attenuator OWC at its natural frequency using fully nonlinear CFD. The effects of chamber geometry on the hydrodynamic performance are investigated by solving the unsteady Reynolds averaged Navier-Stokes equations using ANSYS-Fluent. Comparisons are made with experimental results in both a terminator and an attenuator orientation. The effects of PTO damping, chamber length, and chamber height on the hydrodynamic efficiency are investigated. Increasing the length of the chamber with constant PTO ratio improves the quality of the wave entering the chamber, while decreased length leads to stronger vortices. The optimum PTO coefficient is found to be close to that chosen for the experiments. Reducing the inner skirt height of the chamber significantly reduces all hydrodynamic parameters while a 20 % increase in the chamber's inner skirt height improves the efficiency of the OWC by about 15 %. Observations of the flow field make it clear that reducing the chamber's length can create vortices at the inlet of the OWC. The calculations highlight important nonlinear and viscous effects on the performance of an OWC chamber.