Flow Characteristics in the Spiral Casing of a Water Turbine : 2nd Report, Optimum Configuration

Abstract

In order to establish a design method of the optimum configuration for the spiral casings of water turbines, three different shapes of spiral casings, that is, the decelerated flow type, the free vortex type and the accelerated flow type, are tested and the flow characteristics and losses are compared and discussed. The results show that the optimum configuration is attainable by lowering tangential velocity in a spiral casing to suppress a secondary flow and making the vane angle fit for the flow angle in the range π/2<θ<3π/2. It is also shown that the flow in the spiral casing of a free vortex type is axisymmetric but the total pressure loss of the whole fixed channel is not always the minimum. At the middle of the guide vane channel the velocity and the static pressure become almost axisymmetric for three spiral configurations but the total pressure decreases largely in the rangeπ/2<θ<3π/2 and is different for each spiral configuration. The above tendency is confirmed to be still effective when the upstream boundary layer becomes thick.