A simple model of assessment of collapse aggressiveness of cavitation bubbles suitable for application at pump design stage is proposed. The model is focused on quantifying the energetic effects of single bubble collapses and the emphasis is placed on computational efficiency. The objective of the model is to provide a rapid estimation of the erosion risk for steady-state or near-steady-state flow with traveling bubble cavitation. The proprietary 3-dimensional Navier-Stokes code for turbulent flow in hydrodynamic machinery is coupled with the unreduced Rayleigh-Plesset equation for incompressible liquid by virtue of the iterations of continuity and momentum equations to account for density changes in the bubbly regions (two-way coupling). The model of collapse aggressiveness of the cavitation bubbles is based on the estimation of the energy dissipated between two successive bubble rebounds. The model is tested for a 2-dimensional hydrofoil in the cavitation tunnel of SIGMA Research and Development Institute in Lutin. The closed-loop tunnel is equipped with the acoustic bubble spectrometer to measure the nuclei population in the test section inlet. The erosion pattern of the hydrofoil surface is monitored using optical profilometry. The results indicate the dominant effect of the first (most energetic) collapses, however, the model overestimates the importance of smaller nuclei mainly due to their large number in the spectra. Introduction of a threshold for the minimum collapse energy required to form any erosive potential seems necessary to rectify this deficiency. The model, although aimed to achieve efficiency and simplicity by relying on the single-bubble dynamics, shows good agreement with the experimental evidence. An attempt to apply the model to the 3-dimensional geometry of a mixed-flow pump impeller is also presented. This paper is a report on part one of work in progress. In the second part the results of the ongoing pitting tests will be used to develop a model of erosive potential.
Modeling collapse aggressiveness of cavitation bubbles in hydromachinery
Modellierung der Zerfallsaggressivität von Kavitationsblasen in Wasserkraftmaschinen
2009
7 Seiten, 10 Bilder, 1 Tabelle, 17 Quellen
Conference paper
English
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