Abstract

The energy from a tidal stream is abundant and renewable resource whose power is predictable and sustainable. To generate power effectively from the stream a unique counter rotating type tidal stream power unit, whose tandem rotors drive inner and outer armatures in a generator, has been provided by the authors. At the tidal power station located in narrow straits, the unit needs to be reoriented so that useful output power can be obtained from both flood and ebbing tides.

In this paper, the counter rotating tandem rotor turbine was designed for operation in a bidirectional tidal stream and the performance was analyzed. The maximum output power is somewhat lower than that of the rotors designed exclusively for a unidirectional stream. The relative flow has a positive angle of attack at the leading edge and discharges from the trailing edge along the blade camber. The angular momentum change, namely the rotor work, is seen to always be accompanied with a shock loss at the leading edge.

Introduction

Currently, interest in renewable energy sources is growing worldwide. Among these sources, ocean energy is seen as one of the promising resources that can solve the energy supply depletion problem and cope with the warming global environment due to carbon dioxide emissions from the combustion of fossil fuels. To capture the energy available from the ocean, many methods of energy conversion have been proposed (Antonio, 201 0). One of these methods converts the kinetic energy in a tidal stream via a horizontal or vertical axis turbine. The unit does not adversely affect the surrounding marine environment significantly and is environmentally friendly. For most tidal turbines, the horizontal axis tidal turbine is the most advanced and commercially feasible (Laws and Epps, 2016). The operating principles of such a turbine are similar to wind turbines and it is possible to utilize the design methodology and benefit from advanced technologies in the wind industry (Ng, 2013; Ben Elghali, 2007).

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