Dynamic behaviors of the turbulent cavitating flows based on the Eulerian and Lagrangian viewpoints

In order to investigate the structures of the cavitating flow, a volume fraction transport equation with a hybrid turbulence model has been used to simulate the dynamics of the cavitation phenomenon over a two-dimensional ClarkY hydrofoil (AoA = 8°, σ = 0.8, and Re = 7·10⁵). From the Eulerian viewpoint, the interactions of pressure, vortex structure, and volume fraction have been evaluated, and the results have been validated carefully with the experimental observations. Four different flow stages can be categorized accordingly based on the development of the attached cavity, trailing edge cavities, and re-entrant jet. Furthermore, the Finite-Time Lyapunov Exponent (FTLE) and the corresponding Lagrangian Coherent Structures (LCSs) have been used to separate dynamically distinct regions. Above the upper surface, the liquid flow captured by LCS A could travel along the cavity interface to the trailing edge. Similarly, the LCS C captures the liquid flow below the lower surface that can be attracted into the upper surface. From the corresponding particle tracking, these two flows meet near the trailing edge and mix together to form the re-entrant jet, which can be represented by the LCS B. The current study shows that the LCS approach together with the Eulerian method can help us to have better understandings of the cavitating flow. The Lagrangian analysis especially indicates the underlying flow physics about the mixing process and bubble growth and decline behaviors. Most of the previous related studies only focus on the flow above the upper surface. The LCSs shown in this study also emphasize the importance of the flow structure of the lower surface, which provides more insightful information for the flow control and is worth further investigation.