Empirical modelling of sediment erosion in Francis turbines

Sediment particles passing through the turbine components erode the surface in contact. Gradual removal of base material changes the runner profile and also weakens its structure. One of the major consequences of this is gradual loss of turbine efficiency. Attempts have been made from past researches to develop empirical relations to estimate the effects of sediment erosion in hydraulic turbines.Present study is conducted to identify an appropriate erosion model for Francis turbine. Two standard erosion models have been selected to estimate erosion rates and consecutive reduction in efficiency of the runner. Improved empirical relation to estimate the sediment erosion in Francis runner has been proposed. Comparison of results from the improved empirical relation has been done with the results of experimental measurements at the site.It has been found that sediment data from the site can be analysed to predict the damage in Francis runner due to erosion. The results from the improved erosion model are found to be consistent with the earlier studies and experimental measurements. A simple erosion model as the proposed one can help to formulate appropriate design, operation and maintenance strategy for Francis runner at a specific site conditions.

► Empirical relations can be established to estimate losses due to sediment erosion in Francis turbines.
► Flow factor (Kf) in erosion model defined by IEC-62364 document needs further clarifications.
► Appropriate maintenance schedule can be projected by estimating amount of material removed due to sediment erosion.
► Computation of losses caused by leakage due to erosion of labyrinth seal in Francis turbine is still a challenge.