Characteristics of Twin-Runner Darreus Water-Turbines for Tidal Current Power Generation

Abstract

In order to make the electrical-power generation feasible under the lower tidal-current condition the twin-runner Darreus water-turbine was developed. The counter rotations of twin runners are expected to increase the power output. In order to find out the best distance between the runners the wind-tunnel tests using the subscale model were carried out. At the dimensionless distance of 0.18 the rotational numbers were increased up to 156 percent of those at the single-runner configuration. With this distance the water-channel test was also conducted. It was confirmed that the revolution numbers of the twin runners were increased by 20 percents of those in the single-runner configuration. The increasing effect of speed by a diffuser was investigated. At the stand-alone test of a diffuser in the wind tunnel the velocity of the current passing through the diffuser was accelerated by 1.1 of the free-stream velocity, however, in the water-channel test the subscale Darreus model with the shorter diffuser showed no increasing effect. This was primarily because of the short length of the diffuser to the mouth distance, which was determined from the standpoint of the structural efficiency. The demonstrative power generation test is planned at the Kanmon strait in March, 2012.