Development of Shroudless Francis Turbine

In this study, new design concepts were structured by DOE based on internal flow evaluation by CFD to realize the efficiency improvement, reliability improvement and cost reduction of a medium or small capacity hydro turbine. As a part of new concepts, shroudless type and shroud liner type runner shape were adopted. In shroud liner type, shroud line of meridional plane shape inclines at 45 degrees to rotational axis. By adopting shroud less type, runner can be made not by casting but by cutting work. For medium or small hydroelectric power plant, cost reduction is strongly required in comparison with larger scale hydro one. By adopting shroud liner type, efficiency was improved because of mitigating secondary flow. In addition, to improve reliability, shroud partial band was bonded at inlet of runner. This plays a role to prevent runner blade from breaking by tip rubbing. By using high-speed video camera and CFD analysis, it was clarified that runner outlet cavitation is caused by jet which is leakage in the tip clearance region and that leakage flow of outlet is larger than leakage flow of inlet. Moreover, by using the three-hole Pitot tube, the runner outlet flow distribution was measured and the validity of the design point was verified. Finally, by measurement of pressure on the wall of the stationary parts such as the guide vane, it was clarified that the total pressure loss of guide vane increases in stream-wise direction in low mass flow rate. In this report, the development of the shroudless Francis turbine based on the loss mechanism and flow investigation was described.