可変ピッチ案内羽根を有する波力発電用ラジアルタービン(S21-1 自然の流体エネルギー利用技術(1),S21 自然の流体エネルギー利用技術)

Abstract

In order to develop a high performance radial turbine for wave energy conversion, a radial turbine with pitch-controlled guide vanes has been proposed and investigated experimentally by model testing. As a result, the performances of the presented radial turbine have been clarified under steady flow conditions. Furthermore, it seems that the presented radial turbine is superior to a conventional radial turbine, i.e., a radial turbine with fixed guide vanes. Introduction The performance of radial flow turbines, which can be used for wave energy conversion using the oscillating water column principle, has been studied by a number of authors [1-4, 8]. It was found that the efficiency of radial turbines using reaction-type rotor blading was extremely low [1, 2]. On the other hand, the efficiency of impulse blading is higher according to the studies [3, 4]. However, detailed performance characteristics of impulse-type radial turbines were not found in the literature. In an attempt to fill this gap, performance characteristics were measured on turbines (508.8 mm rotor diameter) with different guide vane geometries by the authors [7]. Performance was also measured for flow radially inward and outward through the turbine, which is made possible by an oscillatory flow rig. As a result, it was clarified by the authors [7] that the turbine efficiency of impulse blading was not so high because there are large differences between the absolute outlet flow angle and setting angle of the downstream guide vane, and the downstream guide vane doesn’t work as a diffuser. In order to overcome the above drawback and enhance the performance of the radial turbine, the authors have proposed a radial turbine with pitch-controlled guide vanes for wave energy conversion. As the first step to an analysis of the presented radial turbine, the turbine characteristics under steady flow conditions have been clarified in the paper. Experimental Apparatus and Procedure The test rig consists of a large piston-cylinder, one end of which is followed by a settling chamber as shown in figure 1. The radial turbine’s axial entry/exit is attached to the settling chamber as shown in figure 2. The piston can be driven back and forth inside the cylinder by means of three ball screws through three nuts fixed to the piston. All three screws are driven by a d.c. servo-motor through chain and sprockets. A computer controls this motor and hence the piston velocity to produce any airflows (intermittently for short periods). The test turbine rotor shaft is coupled to the shaft of a servo-motor-generator through a torque transducer. The motorgenerator is electronically controlled such that the turbine shaft angular velocity is held constant at any set value. The flow rate through the turbine Q, whether it is inhalation (flow from the atmosphere into the rig) or exhalation (flow from the rig to the atmosphere), is measured by Pitot tube survey. The radial flow velocity vR at mean radius rR in the turbine is calculated from Q =ARvR where AR is the flow passage area at mean radius (= 2πrRh). In a typical test, for a particular turbine geometry, the volumetric flow rate Q, pressure difference between settling chamber and atmosphere ∆p, turbine torque To and turbine angular velocity ω are all recorded. Thereby, data for one flow coefficient φ defined in