The Darrieus turbine was developed for wind mill at first. An example of its application to water turbine is found in the Darrieus turbine installed in duct for a low head power generation, but no example is known for application in natural water channel. The authors, therefore, have developed the Darrieus turbine and ocean experiments were conducted with the turbine incorporated in a power generator. Only a few reports are published on the characteristics analysis of Darrieus water turbine as compared with those on the wind mill. Many problems remain to be solved, including analysis of the solidity, number of blades, and starting torque, which are significant indicators for design of water turbine. When applied to the tidal power generation as water turbine, efforts should be also concentrated in clarification of the relationship between the solidity, torque and the output of water turbine, which has widely different Reynold's number from that of wind mill. The authors of present paper have conducted measurement of characteristics of outputs, solidity, number of blades and starting torque from the above viewpoints and analyzed the results.
The Darrieus turbine used in the experiment has three blades arranged at a constant interval around the central axis as shown in Fig.1. As the water turbine is a lift type, the peripheral velocity of blades is faster than the velocity of tidal flow. As it has a feature that it rotates in one direction independently on the direction of water flow, it is suitable for the power generation from tidal flow, the direction of which changes from time to time. The Darrieus turbine used in the experiment has the shape as shown in Fig.2. The mean line between upper and lower surfaces of blade is called as the camber line.
