Sediment erosion in the labyrinths of Francis turbine: A numerical study

Abstract

Development of new hydropower projects in Himalayan regions aims for the efficient performance of the turbine with lesser operation and maintenance cost. Over the past two decades, significant efforts have been made to improve the sediment handling capabilities by the turbine components. In the case of Francis turbines, the design of guide vanes and runner blades were focused on the past to improve the sediment resistivity. However, other components of these machines were not studied from the perspective of sediment erosion. The present work aims to study the sediment erosion in the labyrinth sealings of a prototype Francis turbine, having serious erosion problems. Upper labyrinth sealing and bottom labyrinth sealing were modelled by developing a reference case and the erosion wear in these regions were examined numerically. The flow leaving the gap between stationary guide vanes and the runner enters the top and bottom labyrinth seals. While sediment flows along with the clean water these seals get heavily eroded. The results from the numerical investigation show a distinct pattern of erosion locations in the labyrinth sealings that is similar to the field observation.