Flow Characteristics in the Spiral Casings of a Water Turbine : 1st　Report, Flow Characteristics, and Losses

In order to establish a design method of the optimum configurations for the spiral casings of water turbines, a series of studies are performed. In the first report, the flow characteristics in a fixed channel from a spiral casing to guide vane channels are determined theoretically and experimentally using the configurations of a decelerated flow type of spiral casing. The results show that the flow pattern in a spiral casing is a free vortex rV_θ = C, in which only the value of C changes according to each sectional aerea, and that the flow characteristics in a fixed channel are well predicted by a two-dimensional theory if a suitable flow model is introduced. They also show that the flow characteristics at the middle of a guide vane channel become almost axisymmetric in spite of strong non-axisymmetrisity of the inlet flow into the stay vane channel, while the total pressure decreases largely in the range π/2 ≤ θ ≤ 3/2 due to a mixing loss of the distorted flow and a shock loss at the stay vane inlet