Numerical investigation on the formation of the re-entrant flow and the transformation of varying shedding modes in cloud cavitation

The objective of this paper is to investigate two types of cloud shedding processes around the NACA66 (mod) hydrofoil with emphasis on the formation of the re-entrant flows and the transformation of varying shedding modes. The LES method combines the Schnerr-Sauer cavitation model in OpenFOAM to capture the detailed flow structures. Combining the experimental observation, the cloud shedding process can be divided into main re-entrant flow mode, transition mode, and side re-entrant flow mode. The re-entrant flow is primed from the middle of the attached cavity closure for the main re-entrant flow pattern. The velocity is more stable as it develops in a fan shape towards the leading edge of the hydrofoil. For the side re-entrant flow mode, the rotation and local collapse of cloud cavity in the previous cycle resulted in the incipient of the side re-entrant flow. Compared with the main re-entrant flow, the velocity of the side re-entrant flow fluctuates more significantly. The transition between the side re-entrant flow mode and the main re-entrant flow mode can be characterized by the normalized cavity length (l_max/c) and the cavity shedding frequency (St number).