Review of air turbines for wave energy conversion

The development of air turbines for wave energy conversion has been in continuous evolution starting from conventional turbine to self-rectifying turbine and still in progress. The turbines applied to harness wave energy via a pneumatic type system is called oscillating water column which either has a reaction or impulse principle of operation. The reaction turbines are simple in construction but possess weaknesses such as high rotational speed, less efficiency and narrow operating range. Favorably, the impulse turbines feature low rotational speed, high efficiency and wider operating range which made it inefficient. Recently developed self-rectifying impulse turbines too substantiate these features. In this paper, a review of various types of impulse turbine along with a comparative study has been presented. As a result, self-rectifying axial impulse turbine with linked pitch-controlled guide vanes and self-rectifying radial impulse turbine with active-pitch-controlled guide vanes are found to be predominant in terms of wide operating range of flow coefficients at useful efficiencies. A review of bidirectional flow turbine and a comparison with impulse turbines & reaction turbines have also been reported.