Numerical assessment of cavitation erosion risk on the Delft twisted hydrofoil using a hybrid Eulerian-Lagrangian strategy

Artikel i vetenskaplig tidskrift, 2023

Cavitation damage is a major threat to the life span of fluid machinery and has been a hot research issue in engineering for a long time. The current work aims to show the ability to assess cavitation erosion risk on the twisted hydrofoil using a hybrid Eulerian-Lagrangian solver. The volume of fluid method is used for the liquid-vapor interface of resolved vapor structures, while the discrete bubble model is utilized to track micro-scale unresolvable bubbles. A two-way coupling approach is introduced to enable the transition between resolved cavities and bubbles based on their volume, relative location, and shape. A Lagrangian erosion model considering the effect of asymmetric bubble collapse is proposed to predict cavitation erosion risk. Compared with the experimental result, the current model can accurately identify the high erosion risk regions on the hydrofoil surface. The distribution and intensity of the high impact pressures emitted from bubbles is quantitatively evaluated. In addition, the erosion sensitive zones at different stages of the one cloud cavitation cycle are determined and the hydrodynamic mechanisms of aggressive collapse events are analyzed in detail. The results reveal that the potential erosion risk is highest in areas where primary shedding occurs, which causes the macroscopic cavity to roll up. Bubbles with high impact pressures are mainly focused around the edges of the shedding cavity. The secondary shedding contributes to erosive structure in a limited middle angle of attack area, such that when the primary shedding U-shaped structure evolves and begins to collapse, it becomes less erosive, and only isolated points of erosion is found. Further investigation demonstrates that this is due to a transformation from U-shaped vortex to O-shaped vortex, moving the bubbles gradually away from the hydrofoil surface, thereby reducing the cavitation erosion risk.