Importance of renewable energy has become paramount due to its perennial source and no adverse environmental impact. Ocean is one of the major source of renewable energy where the sun's energy is converted into various natural phenomenon. Southwestern sea in particular, in Korea, has large range of tidal currents with potential for tidal current power generation. Tidal power has great potential for future power and electricity generation because of the massive size of the oceans. The major benefit of tidal power and difference from most renewable energy sources is that it is independent of seasons and weather, that is, it is always constant which makes power generation predictable and makes tidal power a reliable energy source. Horizontal-axis-type turbine appears to be the most technologically and economically viable option for the generation of tidal power. Several studies have shown that single-rotor turbines can obtain a theoretical maximum power coefficient of 59.3 %, whereas dual rotor can obtain a maximum of 64? %. Hence, with the optimization of counter-rotating turbines, more power can be obtained than the single-rotor turbines. Previous studies focus on the performance analysis of the turbine with the variation of distance between the blades. This chapter primarily concentrates on the investigation of the performance analysis and power output of a counter-rotating current turbine by the variation of blade angles by both computational fluid dynamics (CFD) simulation and experiments. Numerical simulations were performed using a commercial finite volume method solver, ANSYS CFX ver.13.0. Experiments were conducted in the water tank with a vertically circulating water channel in the laboratory of Korea Maritime and Ocean University (KMOU) to validate the numerical results. Several experiments were conducted with the fixed front blade angle and varying the rear blade angle and vice versa at various water flow rate. Surface streamlines, torque, total power output, power coefficient ( Cp) etc., were characterized and compared for CFD and experimental cases. The results obtained find good agreement with each other.
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