The Hydrodynamic Aggressiveness of Cavitating Flows in Hydro Turbines

An original validation of the vibratory approach of the cavitation erosion monitoring is presented. Cavitation induced vibrations on a given blade of a large hydro turbine are compared to vibrations induced at the lower guide bearing as well as to the pressure fluctuations in the draft tube. Furthermore, pitting tests are carried out to characterize the cavitation aggressiveness. Coherent power spectra of vibration envelopes are used to derive a scaling factor for cavitation aggressiveness. A significant influence of the downstream level variations on the cavitation aggressiveness is carried out. Statistical processing of broadband signals allows a deeper analysis of the interaction between the cavitation flow dynamics and the wicket gates passing.