Hydrodynamic Response and Pneumatic Energy Capture of an Isolated Mutriku Breakwater OWC Chamber: Effects of PTO Aerodynamic Damping and CFD Validation

Breakwater-integrated Oscillating Water Column (BOWC) performance depends strongly on incident-wave frequency and Power Take-Off (PTO) aerodynamic damping, making experimental validation important for assessing CFD predictions. This study investigates the hydrodynamic and energetic performance of the Mutriku BOWC chamber and validates a Computational Fluid Dynamics (CFD) model against experimental measurements. An isolated 1:36 scale chamber was tested in a controlled wave flume under regular wave conditions. The experimental campaign varied wave period and PTO aerodynamic damping using orifice plates as passive loads. Experimental results showed higher Response Amplitude Operator (RAO) values at longer periods. For Capture Width Ratio (CWR), low-damping configurations with larger orifices (16 mm) improved performance at a specific wave condition (kh = 0.61) but reduced efficiency under other conditions. In contrast, intermediate damping (12 mm) maintained comparatively high CWR values over a broader range of wave conditions. The CFD simulations showed good agreement with experimental measurements, with Normalized Root Mean Square Error (NRMSE) values ranging from 4.19% to 11.31%. These results support the use of the CFD model as a complementary tool to experimental and operational studies at the Mutriku plant, providing a validated framework for assessing chamber hydrodynamics, pneumatic energy capture, and the effects of PTO aerodynamic damping.