Enhancing wave energy conversion in oscillating water column devices using breather valve-based pneumatic regulation: a CFD study

Abstract

This study investigates the hydrodynamic and energy conversion performance of a cylindrical oscillating water column (OWC) device integrated with a breather valve for bidirectional pneumatic regulation. The primary objective is to suppress peak power output under high wave conditions and reduce the required generator rated capacity, thereby improving the load factor and operational efficiency during normal wave conditions. A three-dimensional computational fluid dynamics (CFD) is developed to simulate steady-state and transient flow characteristics, incorporating the nonlinear behavior of the breather valve. Parametric analyses are conducted to evaluate the effects of valve threshold pressure (3–12 kPa) and opening ratio (1 %–6 %) under regular wave conditions. Results reveal that the valve's pressure and flow regulation capabilities increase with the opening ratio, though this effect gradually saturates. Moreover, for a given threshold, a minimum opening ratio is required to achieve stable pressure relief, which decreases with increasing threshold pressure. The optimal configuration (3 kPa threshold with 5 % opening ratio) achieves substantial performance improvements compared to a conventional OWC without a breather valve. Specifically, the rated generator capacity is reduced by 87 % (from 740 kW to 100 kW), average generator efficiency increases by 50 % (from 60.8 % to 90.9 %), and average wave-to-electricity conversion efficiency improves by 46 % (from 10.3 % to 15 %). Additionally, annual energy production increases by 43 %, from 83,000 kWh to 119,000 kWh. These findings highlight the breather valve's effectiveness in stabilizing pneumatic power output and enhancing the overall efficiency of OWC systems.