4.3.1. Erosion Description: San Francisco Francis Turbines

This section compares actual site erosion damage on the turbine with the results from the CFD analysis. The images on the right of Figure 12 show the eroded components of a Francis turbine in SFH. Guide vanes presented a higher erosion rate near the clearance gap around the shaft and at both the leading and trailing edges of the vane since the inward flow accelerates near this region due to the decreasing net head pressure at the guide vane cascade. Regarding the runner, the most eroded areas were located at the leading edge and trailing edge of the blades due to the increase in particle velocity in these areas. Good agreement between numerical erosion results and site erosion was observed when comparing both components. The eroded areas of the runner blades coincided with the areas predicted by the numerical analysis. On the other hand, the eroded areas of the guide vanes did not match perfectly with the numerically predicted areas since the clearance gap near the hub and shroud that forces flow interaction with the shaft was not considered in this study.

**Figure 12.** Erosion profiles in turbine walls.
