Evaluation of effect of micro-vortex generator on dynamic characteristics of unsteady partial cavitating flow over hydrofoil

Abstract

The unsteady characteristics of cavitation induce a series of destructive effects, such as cavitation erosion, vibration, and noise. Passive control of hydrofoil cavitation involves changing the structure or material of the hydrofoil surface, thereby inhibiting cavitation damage, and vortex generators (VGs) are the most popular means of passive control because of their effectiveness, simplicity, and lower production and installation costs. In this study, a new VG structure that can improve the cavitating flow state of a hydrofoil is proposed. A multiphase volume-of-fluid model is used to capture the interface between different phases, the Schnerr–Sauer model is used to describe the cavitation process, and turbulence is modeled by large-eddy simulation. The evolution characteristics of the cavitating flow field around a National Advisory Committee for Aeronautics (NACA) 0015 hydrofoil are investigated numerically both with and without the VG to illustrate its control effect. It is found that the VG can change the hydrodynamic characteristics of the cavitating flow field around the hydrofoil, such as the cavity morphology, the vortex structures, and the peak and power spectral density of the pressure. Upon using Lagrangian coherent structures, the motion state of the fluid particles and the distance between adjacent fluid particles are found to change dramatically with time under the effect of the VG. Upon using dynamic mode decomposition, the VG is found to decrease the energy in the first three modes, whereas that in mode 4 is larger without the VG, thereby suggesting that the VG might help to reduce flow noise. Finally, it is found that the VG converts laminar flow to turbulence, thereby increasing the turbulence intensity of the wake flow field and decreasing the maximum value of the turbulence integral scale.