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ABSTRACT In order to develop a high performance impulse turbine for wave power conversion with air flow rectification system, the impulse turbine has been designed and investigated experimentally by model testing. Then, the running and starting characteristics in irregular ocean waves have been clarified by a computer simulation, taking account of energy conversion efficiency of oscillating water column (OWC). As a result, a suitable choice of design factors has been suggested for the setting angle of guide vane and the rotor profile. INTRODUCTION Several of the wave energy devices being studied under any wave energy program make use of the principle of an oscillating water column (OWC). In such wave energy devices an oscillating water column 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 such as the Wells turbine (Gato and Falcao, 1990; Inoue et al., 1986, 1988; Setoguchi et al., 1998; White, 1995) and other newly proposed turbines (Inoue et al., 1989; Kaneko et al., 1991; Sarmento et al., 1987; Setoguchi et al., 1996, 2000a, 2000b; Takao et al., 1997). However, in general, the self-rectifying turbine has inherent disadvantages: relatively low efficiency and poor starting characteristics because the self-rectifying turbine has symmetrical configuration with respect to the plane perpendicular to the rotor axis in order to operate in bi-directional reciprocating flow. On the other hand, researches and proposals on the wave energy devices using a system of non-return valves for rectifying the airflow, together with a conventional turbine such as the Francis turbine, have been reported so far (Katsuhara et al., 1987; Neal, 1993; Tan et al., 1995; Ueki et al., 2000).
ABSTRACT A number of self-rectifying air turbines for wave power conversion have been proposed over the last decade. However, the noise characteristics of the turbines have not been presented so far. In order to clarify the noise characteristics of the turbines, the experimental investigations have been performed under steady flow conditions in this study. As a result, it is found that the noise characteristics of the impulse type turbines are superior to the Wells type turbines. INTRODUCTION The Wells turbine is a self-rectifying air turbine which is expected to be widely used in wave energy devices with oscillating water columns (OWC) (Gato and Falcao, 1990; Inoue et al., 1985, 1986a, 1986b, 1988; Kaneko et al., 1986; Raghunathan and Tan, 1982; Setoguchi et al., 1986). However, the noise will be a serious problem when a large-scaled Wells turbine is installed in a coastal bank or gully because it is operated essentially at a high rotational speed in the running conditions. For wind turbine generators, a number of studies have been conducted to evaluate the noise from wind turbine in the field (Hubbard et al., 1983). The objective of this paper is to compare the noise characteristics of the turbines for wave power conversion. The types of turbines included in this paper are as follows:Wells turbine with high solidity (Inoue et al., 1986a, 1986b, 1988; Kaneko et al., 1986; Setoguchi et al., 1986); Wells turbine with optimum solidity (Inoue et al., 1986a, 1986b, 1988; Kaneko et al., 1986; Setoguchi et al., 1986); Wells turbine with guide vanes (Gato and Falcao, 1990; Inoue et al., 1985; Setoguchi et al., 1998); impulse turbine with self-pitch-controlled guide vanes (Setoguchi et al, 1996); impulse turbine with fixed guide vanes (Setoguchi et al., 2000).
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