In order to improve the performance of a Wells turbine, the porous fences have been equipped on the hub wall in the upstream and downstream of rotor. The effects of the gap between porous fence and rotor, porosity and height of porous fence have been investigated by model testing. The results have been compared with those of the case without porous fences. It is found that the starting characteristics are improved by the porous fences. Furthermore most of the configurations tested have shown improvements in the operation range primarily by postponement of stall. A suitable choice of design parameters for the turbine has been suggested.
Several of the wave energy devices currently studied in the United Kingdom, Japan, Portugal, India and other countries make use of the principle of oscillating wave-air column for converting wave energy to low pressure pneumatic energy which in turn can be converted into mechanical energy. In this case, the development of bi-directional air turbine has come up as an important problem. So far, a number of self-rectifying air turbines with different configurations were proposed, including Wells turbine (Gato et al.,1988; Inoue et al.,1986a; Raghunathan et aI., 1987; Raghunathan, 1995; Suzuki et aI., 1985; White, 1995), turbine using pitch-controlled blades (Raghunathan et aI.,1997; Sarmento et aI.,1987; Takao et al.,1997), impulse turbine with self-pitch- controlled guide vanes (Setoguchi et al.,1993) and so on (Kaneko et al.,1992). Among them the most promising turbine is the Wells turbine at present. There are several reports on the performance of the Wells turbine and factors which have an influence on the performance (Raghunathan, 1995). For the performance of the Wells turbine, in general, the running characteristics is improved with decreasing solidity of the rotor. On the other hand, the starting characteristics is deteriorated for low-solidity Wells turbine. These facts mean that the starting characteristics should be improved for low-solidity Wells turbine to convert much fluid energy into mechanical energy of rotation.
