On the Transition from Sheet to Cloud Cavitation

Hydraulic components failures due to cavitation erosion are mostly a common cause of false or unfavorable operating parameters. In a parameter study with a convergent divergent nozzle, we found a flow change from sheet cavitation to a more aggressive cloud cavitation. This transition occurs at a critical Reynolds number. The critical Reynolds number was found to be the same for water and a glycol water mixture (increased cinematic viscosity by a factor of 1.16) as one would expect on the grounds of the Bridgman postulate. The critical Reynolds number, hence the transition point, is predicted by a physical model developed on first principles: The transition point is reached, when the time for sheet growth is the same than the time needed for the reentrant jet to reach the sheet leading edge. If this is the case, the reentrant jets cut of the sheet and detach closed clouds. To predict the critical Reynolds number is of great value for the industry, since harm full operation points can be identified already in the design process.

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