Abstract
This research project introduces a novel hydrokinetic turbine system called a direct-drive parallel-stream counter-rotating darrieus turbine (DD-PS-CRDT). Two darrieus rotors are arranged horizontally across the water stream, one directly driving an armature coil rotor and the other a permanent magnet rotor of a generator. The proposed system improves on other counter-rotating turbine systems because each rotor utilizes a separate stream, direct-drive eliminates friction losses in the gearbox and the generator's rotational speed is doubled. This study emulated the DD-PS-CRDT by writing a simulation program using Visual Basic and Matlab codes. Turbine system configurations had different numbers of blades and lag angles between the rotors. Torque coefficient (CT) profiles and ripples were investigated in the interest of torque output smoothing. The system with the lowest ripple was found and a table of prescribed lag angles presented. It is noted that both the magnitude of the minimum ripple and the corresponding lag angle change with rotational speed (ni). Moreover, the CT output profile varies greatly with ni and a few curves contain irregular spikes. However, the evidence suggests that it is possible to maintain smooth curves, especially at the rated speed (ns).