Development of high-efficiency and low-cost shroudless turbine for small hydropower generation plant

Hydropower generation is now attracting attention because of the world's energy problems. With cooperation from the industrial, governmental, and academic sectors, a new type of Francis turbine runner was developed for the Kazunogawa small hydropower generation plant. To validate its performance, a model turbine test facility was built at Waseda University, and a performance test was performed. This experiment confirmed that the maximum hydraulic efficiency was about 88%, and the operational point of maximum efficiency agreed with the design point. Then, using a high-speed video camera, three-hole pitot tube, and computational fluid dynamics (CFD) with cavitation analysis, the loss generation mechanism of the turbine was clarified. In addition, a vibratory cavitation erosion test was carried out to select the material for a prototype runner. It was found that the volume loss of ALBC was lower than that of any other material. At the first stage of prototype turbine design, a design point that could generate the maximum output for a year was calculated using the flow duration curve at the installation location. Then, the loss in the casing and double circular cascade was improved using CFD. Performance and load rejection tests were performed before the prototype turbine operation. It was confirmed that the maximum efficiency was 91%, and the runaway speed was lower than the value predicted by the model turbine test.