Numerical analysis of an onshore oscillating water column wave energy converter for different wall slopes

Abstract

An alternative to the energy matrix expansion, due to the increase of global electricity demand, is the renewable sea wave energy source, which has high energy potential. The Oscillating Water Column (OWC) converter is one of the most studied, although it is not yet used at commercial scale. Therefore, searching the optimal geometric configuration is fundamental to turn this device viable. This study proposes a numerical analysis of an onshore OWC for different slopes of chamber walls (from 40o to 90o) and equipped with a Wells turbine. Simulations of incompressible 2D flows are performed by means of the FLUENT® software, which is based on Reynolds-averaged Navier-Stokes (RANS) equations. The k-ɛ turbulence model and the Volume of Fluid (VOF) method are employed. Analyses of the behavior of run up/down in the front wall, sloshing inside the chamber and the energy balance of the OWC are carried out for incident waves with periods from 6 to 12 s and height of 1.5 m. Chamber with wall slope of 40o reaches the highest extracted energy (EE) at wave periods of 9 s and 10.5 s (70% of the incident wave energy) and higher run-up/down on the front wall and sloshing inside the chamber. However, chamber with wall slope of 90o has more regularity of EE at the range of wave periods, which allows concluding that the choice of the optimal wall slope depends mainly on the sea state characteristics.