Sediment erosion in hydro turbines and its effect on the flow around guide vanes of Francis turbine.

Erosion of material surface due to collision of solid particles has been a challenge to several fields of engineering. Despite of centuries of investigations and research, the exact phenomenon of erosion of surface by the solid particles has not been fully understood. Increasing number of hydropower plants are being built in the regions where rivers are heavily loaded with sediments. This induces material erosion in hydro turbines, leading to change in flow pattern, losses in efficiency, vibrations and even final breakdown of turbine components. To overcome sediment erosion related failures, development of erosion resistant alloys, coatings of the components, and optimization of hydraulic design of the components, are the important practices. In Francis turbines, erosion causes increase of clearance gap between guide vanes and facing plates and cross flow occurs from this increased gap. This cross flow together with other secondary flows disturbs the velocity profile at the runner inlet. Change in velocity profile at the inlet causes additional erosion damage and other undesired effects in the turbine runner. Most of the past studies in Francis turbine were focused to understand the flow phenomenon inside the turbine components and to analyze their effects on design improvements. There is still a need of further fundamental research to understand the effects of sediment erosion of turbine components on the flow phenomenon, and developing better designs of hydro turbines to minimize those effects. [ABSTRACT FROM AUTHOR]