Performance analysis of sand-casted model Francis runner with detachable blade: efficiency measurement, and evaluation

Hydropower is an emission-free technology that harnesses energy from flowing water. Francis turbines have been widely utilized in hydropower plants. The complex process of manufacturing turbines requires highly trained labor and special equipment. Most hydraulic turbines are composed of steel; however, there are a few low-head turbines are made of cast iron and bronze. In this study, a 2 kW model Francis turbine was developed with a detachable blade using the sand-casting technique. The existing design of a 2 kW Francis runner available at TTL was utilized for this study. The existing design was modified such that one of the blades was made detachable. The modification was also made to ease the fabrication process using the sandcasting method. The runner was separated into four different components, namely the hub, shroud, normal blades, and detachable blade segment. All four different components were 3D printed with PLA material, and the 3D printed models were used as molds for sand casting. The sand casting was performed at a local sand-casting shop. The sand-cast components were machined and polished before assembly. After the assembly, the components were joined together with brazing. The detachable blade was made such that it can be attached using a bolted joint. The major advantage of this design was that one of the blades could be detached and observed separately. This type of design can be used for the study and research of the erosion characteristics of Francis runner blades. The efficiency of the thus fabricated runner was measured to be 45% and 43.4% at heads of 4.3m and 4.1m, respectively. This study has demonstrated that small-scale Francis runners can be fabricated with the techniques of 3D printing and sand casting.