A systematic numerical investigation on the hydrodynamic performance of an oscillating water column (OWC) system for different damping values from the power take-off (PTO) device and at different model scales has been studied. Further, an experimental programme was devised with a Froude model scale of 1:12 in a shallow wave flume by representing PTO damping by varying the air orifice ratio, a/A [ratio of air orifice area (a) to plan area (A)]. In the case of numerical investigation, simulation was carried out in the computational fluid dynamics (CFD) model, REEF3D. Herein, the equivalent PTO damping on the OWC chamber is represented by the porous media flow relation. First, the numerical results are validated by comparing with the laboratory measurements for five different PTO damping. Second, following the validation stage, the open-source numerical model is used to evaluate model scale effects on the hydrodynamic performance of the OWC by comparing hydrodynamic parameters of four different model scales from 1:12 to full scale. In this paper, the influence of PTO damping and model scales on the variation of pressure behind the lip wall, air pressure, and hydrodynamic efficiency is studied. The results are reported for different relative water depths. Since the air is modelled as incompressible, the effect of scaling on the hydrodynamic performance of OWC is found with negligible variation.