Development and validation of a cavitation erosion model

Cavitation erosion is a major issue in the working life of hydraulic turbomachines. Vapour formation and bubbles’ implosions can lead to the damage of the solid boundaries, provoking performance losses and fatigue failure over time. This paper aims at validating a new approach of
cavitation erosion prediction, reproducing a circular sector of the stainless-steel nozzle used in the experiment of J. P. Franc1. The Singhal et al. Full Cavitation Model2, based on the bubble dynamics
treatment, is implemented in conjunction with the k-omega SST turbulence model within Ansys Fluent.
Bubbles detached from the cavitation cloud collapse close to the solid surfaces, whenever the static pressure of the target plate is higher than the vapour pressure. In the ultimate life stage of an imploding bubble, a microjet is formed; subsequently the jet may impact on the solid boundaries of a working machine. If the microjet velocity overcomes the material critical velocity, a function of the material yield strength, a permanent deformation finally occurs. The developed cavitation erosion model accounts for the number of implosions in the unit volume, giving different importance to the erosive mechanisms, according to the amount of vapour collapsed in the target plate cells. Time averaged results of the numerical simulations are compared against the nozzle experimental results, displaying the cavitation erosion mid-line annular locations.