Erosion vibratory fingerprint of leading edge cavitation of a NACA profile and of a Francis model and prototype hydroturbine

This paper summarizes the findings of CEA project No 307 G 657 entitled "Hydraulic Turbine Cavitation Pitting Detection by Monitoring Runner Vibration." The project was centered on the detection of leading edge cavitation, the main cause of erosion damage on Francis turbines. Based on a damage model proposed by EPFL and verified by EPFL and IREQ, the vibratory signature of erosive cavitation was first sought on a bi-dimensional NACA 009 profile in a high speed cavitation tunnel and then on the model and the prototype of a Francis turbine design. The main results of these investigations are presented. These show that the damage mechanism observed in the cavitation tunnel appears to also apply to the model and the prototype but its vibratory signature is modified and is determined by overall system flow characteristics that can vary from model to prototype if complete system homology is not maintained. Appropriate measurements on the fixed part of the machine were found to be equivalent to those made on the rotating part.