Abstract

Tidal energy is one of the most promising emerging renewable energy sources which remains largely untapped, due primarily to the challenges of submerged operation within sensitive marine environments. Extracting kinetic energy from dense and energetic flow streams which vary in height, reverse flow direction roughly twice a day and carry sediment as well as marine life requires a unique application of engineering knowledge. A variety of tidal turbine technologies have been developed in response, although as yet the industry is far from mature and there remains great potential for improvement. The research presented in this study introduces a new type of turbine design which has been developed specifically to address the issue of balancing marine friendly technology with efficient energy harvest. This is accomplished through the use of an open-centre concept which houses the blades between the hub and shroud, thus minimizing the risk of blade tip impact and providing free passage through the central aperture.
In this study several iterations of the design are tested using the methods of computational fluid dynamics (CFD), each one featuring a different helical blade geometry of varying length and twist angle. A numerical model of the new design is presented in which the energy generation potential is assessed by measuring the amount of torque produced by a stationary blade placed in a steady flow. The torque is calculated by determining the pressure force acting on each blade surface and the resulting moment generated about the rotation axis of the turbine. This method allows for a great number of geometries to be tested under simulated turbine operating conditions, without requiring a prohibitive amount of computational resources. The initial assessment of this new type of turbine is promising, indicating that certain blade geometries produce a greater amount of torque than a model of the conventional open-centre turbine developed by OpenHydro.