This paper provides an accurate description of the steady three-dimensional flow-field in a high solidity Wells turbine to be used in an oscillatory water column (OWC) device for wave energy conversion. The analysis has been performed by solving numerically the incompressible Navier-Stokes equations in a non-inertial reference frame rotating with the turbine. Turbulence effects are taken into account via a Reynolds-average approach, the turbulent stresses being evaluated by means of the Spalart-Allmaras model. Using a very fine mesh, a quite good agreement with experimental data has been obtained in terms of efficiency, torque, and total pressure drop, at different flow rates. Moreover, the tip clearance has been properly modeled and the effect of the tip-gap on the turbine performance has been analyzed in details. (C) 2007 Elsevier Ltd. All rights reserved.