Influence of turbine damping on OWC wave-to-wire performance

Abstract

Turbine-chamber coupling is a decisive factor in the performance of oscillating water column (OWC) wave energy converters. In this study, a wave-to-wire model is developed to evaluate the influence of turbine-induced damping on the different energy conversion stages—pneumatic, mechanical, and electrical—of an OWC equipped with a biradial turbine. The methodology combines: (i) high-resolution spectral modelling to characterize the nearshore wave energy resources at a study site in Galicia (NW Spain); (ii) physical (laboratory) and computational fluid dynamics (CFD) modelling of the OWC hydrodynamics accounting for air compressibility; and (iii) analytical modelling of the turbine–generator set, including a control law for rotational speed regulation. Results show that turbine-induced damping critically affects the performance of OWC devices across all energy conversion stages, with the optimal damping condition varying according to the stage considered. Mechanical efficiency emerges as a key factor, which can shift the optimal damping towards higher values than those indicated by the pneumatic efficiency alone. These findings underscore the importance of turbine efficiency in OWC design and highlight the need to integrate mechanical and electrical conversion stages into turbine-chamber coupling strategies to achieve optimal performance.