Self-rectifying air turbines for wave energy conversion: A comparative analysis

The oscillating water column (OWC) with an air turbine is a major class of wave energy converter that has been object of extensive research and development effort over many years, including the deployment of prototypes into the sea. In an OWC, the air alternately flows from the chamber to the atmosphere and back. Unless check valves are used, the turbines are self-rectifying, i.e. their rotational direction remains unchanged regardless of the direction of the air flow. The paper presents a comparative study of the performance of various types of self-rectifying air turbines and their suitability to different OWC applications and energy levels of the local wave climate. The study is based on available information on results from laboratory testing at Reynolds numbers high enough to make those results representative of full-sized machine performance under real operating conditions. Average values of flow rate, pressure head and efficiency are used in the comparisons, based on a stochastic approach in which the pressure oscillations in the OWC air chamber are assumed to be a random Gaussian process.