A Study on the Effects of Blade Profile and Non-Uniform Tip Clearance of the Wells Turbine

Several of wave energy devices being studied under many wave energy programs in the United Kingdom, Japan, Portugal, India and other countries make use of the principle of an oscillating water column (OWC). In such wave energy devices, a water column which oscillates due to wave motion is used to drive an oscillating air column which is converted into mechanical energy. The energy conversion from the oscillating air column can be achieved by using a self-rectifying air turbine. Wells turbine is a self-rectifying air turbine which is expected to be widely used in wave energy devices with OWC. There are many reports which describe the performance of Wells turbine both at starting and running characteristics. According to these results, Wells turbine has inherent disadvantages: lower efficiency, poorer starting and higher noise level in comparison with conventional turbines. In order to enhance the performance of Wells turbine, some rotor blade profiles have been recommended by various researchers. The aim of this study is to investigate the effect of rotor blade profile on the performance of Wells turbine. In the study, four kinds of blade profile were selected and tested by model testing under steady flow condition. The types of blade profile are as follows: NACA0020; NACA0015; modified NACA0015; and modified Eppler472. The experimental investigations have been performed by use of test section with a casing diameter of 300 mm. Further, the effect of non-uniform tip clearance on the turbine performance was tested and the result was compared with that of the case of Wells turbine with uniform tip clearance. As an additional experiment, the effects of blade profile and non-uniform tip clearance on the performance under unsteady flow condition have been investigated numerically by using a quasi-steady analysis.