Design and performance analysis of a passive rotatable deflector diversion tail for tidal current power generation hydrokinetic turbines

In the present study, a deflector that can passively rotate is designed for use on a hydrokinetic turbine that generates power from tidal currents. This deflector is capable of self-adjusting its position with changes in the water flow, so that the hydrokinetic turbine can generate maximum power at both high and low tides. The purpose of this study is to maximize the output power of a hydrokinetic turbine by improving the geometry of the deflector and the diversion tail. The rotation of both the turbine and the deflector are simulated with finite element analysis software. In addition, the accuracy of the simulation results is verified through experimental tests. The improved design of the deflector and the diversion tail is considered in terms of the parameters, including the deflector reduction angle, the gap between the deflector and the turbine, and the height of the diversion tail. The geometrical design of the deflector and the diversion tail is compared to a turbine without the deflector and to another turbine with the original deflector over the entire operating range using CFD simulations. Without the deflector, the maximum power coefficient of the turbine was 0.0979 at a tip-speed ratio of 0.4, whereas the maximum power coefficient of the turbine was 0.306 at a tip speed ratio of 0.57 when using the improved deflector. The results indicate that, after adding the improved deflector, the power coefficient of the turbine was 3.13 times greater compared with the turbine without the deflector and 18% greater compared with the turbine equipped with the original deflector.