Spectrum normalization method in vibro-acoustical diagnostic measurements of hydroturbine cavitation

摘要

Full-scale vibro-acoustical diagnostic measurements of cavitation in four Francis 6 MW double runner turbines were performed. Two types of sensors were used a hydrophone sensing waterborne noise at the pressure side of a runner and anaccelerometer mounted at various points at the outer turbine casing, facing the runner's pressure side. The correlation of noise and acceleration intensity with suction-side pressure fluctuations and runner position was checked. A simple but efficientmethod of spectrum normalization, which rejects the influence of the measurement set characteristics and vibro-acoustical characteristics of a turbine, was developed. The resulting spectra reveal the dependence of cavitation source strength on the turbine power as a function of noise or acceleration frequency.