Study of erosion-induced leakage flow in guide vane of Francis turbine using erosion-coupled mesh deformation simulations

Erosion of the hydro-turbine components in sediment-laden flows results in a reduction in the efficiency and life of turbine components. The particles in the water affect the operation of both stationary and dynamic components. In the present study, the guide vanes and facing plates of a Francis turbine are numerically investigated regarding their susceptibility towards erosion using an erosion-induced geometry deformation approach. The effects of non-uniform changes in the clearance gap between the guide vanes and facing plates on the erosion and leakage flow are explored. A segment of the actual distributor is analysed for the design and part load operation of the turbine. The simulations were performed for a period equivalent to 2400 h and the comparisons are drawn with the geometry at the end of 240 and 1200 h, respectively. The results show an increase in thickness loss with operation time, however, the position of maximum thickness loss shifted towards the tailing edge for guide vanes and towards center for the face plate. The increase in clearance gap leads to higher cross-flow across the clearance gap and thus, the crossflow and the erosion rate feed off each other. The erosion of the guide vane and face plate was symmetric for BEP but asymmetric for PL. Further, the simulations were performed with three different initial clearance gaps ranging from 0.5 mm to 1.5 mm highlighting the changes in erosion rate for different clearances. The present work provides important engineering insights for the design and operation of the Francis turbine guide vanes to control their erosion and leakage flow.