The present study investigates the efficiency of a vertical axis tidal current turbine for various conditions of the number of blades and layers experimentally and numerically. The vertical axis tidal current turbine is of drag force type and has arch-shaped blades. From experiments in a circulating water channel and numerical simulations using a commercial computational fluid dynamics program, torque, angular velocity, power coefficient and tip speed ratio of the vertical axis tidal current turbine are obtained. Based on the results with the various conditions, the relationships between the properties are examined. The maximum power coefficients occur at the tip speed ratio of about 0.4~0.5. It is also found that the doubled layer turbine gives the 35% larger power coefficient than the single layer one.
There are various kinds of renewable energy in the ocean. Among many ocean renewable energy sources, tidal current power is regarded as a reliable and predictable energy source unlike other irregular energy ones such as offshore wind and wave. A tidal current power system also causes no significant environmental impact due to power plant constructions since it does not need to build structures such as a dam disturbing ecosystem severely. Thus, a tidal current can be one of the favorable energy sources in the aspects of steadiness and environments. Tidal current power is one of the main renewable energy resources in Korea whose west and south coasts have strong currents potentials. There have been many studies focusing on tidal current power systems. Garbuglia et al. (1993) and Paish et al. (1995) introduced a new concept of tidal stream power system through field experiments. Jo et al. (2008) conducted the experimental study of tidal current power systems tested in the water channel. To achieve the maximum production of power, many studies of tidal current power system have been carried out with the various geometrical and environmental conditions.
