Numerical prediction of hydrodynamic cavitating flow structures and their corresponding erosion

Hydrodynamic cavitating flows usually consist of 3-D intense vortical flows that are detached from solid boundaries. Detached vortical flows normally generate heaps of cavitating flow structures, which, in turn, govern the location of cavitation erosion before collapse. Thus, this study introduces a new numerical approach based on the improved delayed detached eddy simulation (IDDES) turbulence modeling for predicting cavitating flows. Then, the solution of compressible Eulerian-Eulerian two-phase flow and the IDDES turbulence model was linked to the microjet hypothesis and unsteady behavior of pressure and vapor volume to predict the corresponding erosion of cavitating flows. The method for cavitation erosion prediction, a modified version taken from previous studies, was applied as a post-processing tool. The validation of cavitating flow predictions was performed for the first time on the Grenoble axisymmetric nozzle by comparing them with 21 photos of cavitation from the previous experimental study. The results showed that the present numerical approach estimated various features of hydrodynamic cavitation well, including shedding processes and the length, shape, and collapse of cavitating structures. Using the numerical analysis, three main stages were detected for the present cavitating flow, and the vorticity-cavitation interactions were investigated by the vorticity transport equation. The streak-like and tube-like cavitating (STLIC and TULIC) structures were introduced in the second stage, initiated by flow instability, and entirely governed by corresponding turbulent flow structures. The collapse of these cavitating structures is one of the primary sources of cavitation erosion on lower and upper walls. The results of the numerical erosion predictions were compared with those of the previous erosion tests on the Grenoble axisymmetric nozzle. Satisfactory numerical performance was achieved in predicting the location and intensity of cavitation erosion.