Shedding frequency in cavitation erosion evolution tracking
Résumé
Cavitation erosion is a concern for most hydro machine operation. An especially damaging type of cavitation is the cloud cavitation. This type has a growth-collapse cycle in which a group of vapor bubbles grows together in a low-pressure region, to collapse almost simultaneously when the pressure recovers. Measuring the frequency of these collapse events is possible by acoustic emission (AE), as demonstrated in this study, in which a cavitation tunnel is utilized to create cloud cavitation on a sample surface. These samples were fitted with AE sensors, and the initially high frequency AE signal was demodulated to detect the relatively low frequency cloud cavitation shedding. When the cavitation number is increased, AE detects the changes in this frequency correctly, confirmed by comparing the results to video analysis and to simulations by other authors. Additionally, the frequency increases when cavitation erosion progresses, thus it provides means to track the erosion stage. The presented method can be used in detecting the transition from cloud to sheet cavitation when the cavitation number is increased, and in tracking erosion evolution in the cavitation tunnel. The method could probably be extended to hydro machine monitoring, as this type of cloud cavitation is common in hydrofoils.
Origine : Fichiers produits par l'(les) auteur(s)
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