The performance of an oscillating water column (OWC) device, obtained from computations, was validated with experimental results. The current numerical code showed good agreement with experimental data and also with mathematical models. The base model which recorded rotor power of 0.17 W and efficiency of 8.28 % was then modified–the OWC chamber geometry and the rotor geometry were modified. The best model recorded rotor power and efficiency of 0.34 W and 16.1 %, respectively. Comparing this with the base model, the improvement in rotor efficiency was approximately 94 %. The flow conditions in the current numerical work were fixed and rotor speed was also kept constant. The work highlights that the performance of the rotor at fixed condition can be improved by optimizing the OWC chamber geometry and the rotor design. Furthermore, the current work also highlights that the design of the rotor is strongly influenced by the OWC chamber it is employed in.