AbstractThis paper describes a numerical evaluation of optimal sizes of a Wells turbine and chamber cross section to be used in a cluster of an oscillating water column (OWC) wave energy converter device. The FLUENT numerical model, based on the Reynolds–averaged Navier–Stokes equations and the volume of fluid technique, is used for modeling hydrodynamic and aerodynamic flows. Two new methods are developed for diminishing the computational cost: the generalized–TDO (turbine diameter optimization) model and the HAS (hydro-aerodynamic similarity) model. The generalized–TDO model is developed to determine the optimal turbine diameter for an OWC chamber with a square cross section. The analytical HAS model employs a similitude method to extend results obtained for a square cross section of the OWC chamber to a rectangular one. The optimal length, B, and width, W, of the chambers and turbine diameter, D, chosen by taking into account the southern Brazilian wave climate, were B × W = 15 × 15 m2 and D = 2.75 to 3.00 m and 20 × 20 m2 and D = 3.25 to 3.50 m, with efficiencies of 51% and 49%, respectively. Same optimal annual efficiency can be obtained for rectangular cross-section chambers 15 × W and 20 × W by using an adequate turbine diameter defined by the HAS model.