Optimization of the Rear Propeller Profile of a Counter-Rotating Type Tidal Stream Power Unit Based on CFD Simulation

In order to convert the kinetic energy of tidal stream, the authors have invented a novel counter-rotating type tidal-stream power unit, which is composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. The commercial code (GH-Tidal Bladed) and academic in-house code (SERG-Tidal) based on blade element momentum theory have been proven well applied to performance prediction for the traditional wind turbine and tidal turbine. However, for the counter-rotating type tidal turbine, it is very difficult to simulate the mutual effect between the tandem propellers using blade element momentum. This paper sets up a CFD model for the counter-rotating type tidal turbine and optimizes the chord and pitch distribution of the rear propeller. The predicted results are compared between the original turbine and optimized turbine, which show great improvement in power efficient after optimization.

Counter-Rotating Type Tidal-Stream Power Unit Playing Favorable Features in Various Ocean Circumstances

The authors have invented the unique counter-rotating type tidal-stream power unit, which is composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. In the unit of the downstream type, the front and the rear propellers counter-drive the outer and the inner armatures of the peculiar generator respectively, in keeping the rotational torque counter-balanced between both propellers/armatures. This paper discusses and verifies experimentally the almighty features of the power unit. The axial force acting on the pillar increases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Besides, the tandem propellers bring the symmetrical vertical force from side to side though the single propeller brings the force in one direction. The counter-balanced torque makes it possible to moor the power unit with only one cable/wire/rope, and the behavior of the submerged unit was confirmed experimentally.