Experimental investigation and further development of the cavitation erosion scale effects and the cavitation erosion model

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Hydrodynamic cavitation and the resulting cavitation erosion remain serious and hardly predictable problems. The empirically deduced design guidelines are used to avoid cavitation in hydro power facilities. However these guidelines depend on the design discharge. Thus the climate change and the resulting increase in flood discharges pose severe threats to the facility safety. Therefore the present research project seeks to clarify the basic mechanism of hydrodynamic cavitation erosion and to make damage predictable. Former research campaigns already have empirically elucidated the cavitation erosion scale effects, especially concerning civil engineering materials. However the applicability remains unclear due to a lack of knowledge of the actual damage mechanism. The microscopic damage process which was found in single bubble experiments could not yet be transferred to bubble ensembles in hydrodynamic cavitation. A new, promising cavitation erosion model postulates a relation between the cavitation cloud behaviour and the erosion. The coherent collapse of a cavitation cloud induces a micro jet in a boundary near bubble. The present project investigates the dynamics and scale effects of the cavitation cloud by time resolved optical observation to clarify correlations to the erosion. The actual damage process of hydrodynamic cavitation will be observed with a time resolved, microscopic method. Amplitude, frequency of micro jets and its temporal and special correlation cloud behaviour and damage patterns are analysed. The research will yield basic knowledge about the actual damage mechanism and the fundamentals and transferability of scale effects. It will verify the current cavitation erosion model.