This paper reviews the present state of art of the self-rectifying air turbines those could be used for wave energy conversion. These include the following:
Wells turbine (with or without guide vanes),
turbine with self-pitch-controlled blades,
Wells turbine with leading edge slat,
biplane Wells turbine (with or without guide vanes),
biplane turbine using cambered blades,
biplane turbine using preset blade incidence,
triplane Wells turbine,
impulse turbine with self-pitch-controlled guide vanes,
McCormick turbine,
radial turbine,
cross flow turbine and
Savonius turbine.
The performances of them have been compared from the viewpoints of the starting and running characteristics. It is concluded that the biplane Wells turbine with outer guide vanes has the best performance, and for which a suitable choice of design factors has been suggested.
Several of the wave energy devices being studied under any wave energy program make use of the principle of an oscillating water column. In such wave energy devices an oscillating water column due to wave motion is used to drive an oscillating air column which is converted into mechanical energy. The energy conversion from an oscillating air column can be achieved by using a system of non-return valves for rectifying the air-flow, together with a conventional turbine (Katsuhara, 1987). But such a system is complicated and difficult to maintain, and the average cycle efficiency in an oscillating air-flow is likely to be considerably smaller. The non-return valves can be eliminated by the use of a self-rectifying air turbine which inherently provides a unidirectional rotation for an alternating air-flow.
