Cavitation Damage Detection Through Acoustic Emissions

Cavitation in hydraulic machinery is a common phenomenon with high potential for causing damage. Often it is not known whether the machinery is damaged by cavitation or cavitation occurs at all. With regard to predictive maintenance it would be advantageous not only to detect cavitation, but also to determine the current condition or damage of the hydraulic machinery. Knowing the current condition of the machinery, maintenance could be planned properly ahead and unnecessary downtime could be avoided. Since visual inspection of the current status i.e. state of cavitation and possible damage of the machinery is usually not possible due to missing optical access, acoustic inspection offers an alternative. In order to determine whether and how damage results in changes in acoustics, experiments in a controlled environment were conducted using a hydrofoil. The hydrofoil was placed in a cavitation-channel and exposed to strong cavitation for a defined period of time. Afterwards measurements of acoustic signals at different flow conditions with different cavitation conditions including no cavitation were conducted. The measurement procedure was repeated for several hundreds of times. So various measured acoustic signals of different cavitation damage states on the hydrofoil were captured. Since it was not known in which frequency region changes may occur due to cavitation damage, a broad frequency region reaching from several Hz up to 1MHz was investigated. The experiment shows promising results, such that cavitation damage at the hydrofoil results in significant changes in acoustics. Further different behavior in different frequency ranges and flow conditions can be observed.