The present study deals with the numerical study of the micro-jet velocity and the cavitation - erosion on an axisymmetric nozzle, which presents high ow unsteadiness and aggressiveness. The proposed model is based on energy conservation for the micro-jet velocity prediction, and assumes the potential and kinetic energies, at the start and at the end of the cavity collapse, respectively. The mass transport between liquid and vapor is closely related to Rayleigh Plesset's equation. Results have been obtained with a numerical scheme assuming homogeneous mixture ow, implicit LES and Zwart-Gerber-Belamri cavitation model. The 3D unsteady ow simulation has been solved using OpenFOAM, whilst for the micro-jet estimation, Python language coupled with OpenFOAM's calculator have been used. Results clearly show that the implemented model captures adequately the phenomenon and enables to identify attacked areas. Outcomes agree reasonably with the experimental results obtained by Franc in the Laboratoire de Ecoulements G eophysiques et Industriels. Furthermore, results of the implemented Zwart- Gerber-Belamri cavitation model with adaptive time step, showed more details related to the cavitation shedding and detachment, which are important factors to predict erosion.