Unsteady computational fluid dynamics analysis of the hydrodynamic instabilities in a reversible Francis turbine used in a storage plant

The state-of-art of design and research for Pelton turbine casing, weight estimation, counterpressure operation and scientific challenges

The Pelton turbine is the most widespread and efficient impulse hydropower turbine. The Pelton casing is a static, but key component: the internal hydrodynamic phenomena affect the performance of the hydropower plant, the vibration of the equipment and water quality (dissolved oxygen downstream). However, the literature information is very fragmented and not well organized, so that the design is generally based on empirical rules and on proper know-how of hydropower companies. In this paper, the state-of-the-art of the Pelton casing is reviewed and organized under three macro areas: hydraulics, mechanics (vibrations and weight) and aeration. The preliminary design procedure is described and discussed in light of recent scientific results, and the open questions and research challenges are highlighted. Innovative case studies are described (including counterpressure operation) and a dataset of installed casings (not available in literature) is elaborated to derive an empirical equation to estimate the casing weight. The efficiency can be improved by 3% by an optimal fluid dynamic design and a better understanding of the internal hydrodynamics. Proper inserts can improve the hydraulic efficiency by 2%, reduce the weight (by about 12%) and better bear the vibrations. Several scientific questions are still open, and a better understanding of the fluid structure interaction is needed to improve efficiency, operation and water quality.