STUDY OF TURBULENT VORTEX AND HYDRAULIC DYNAMICS IN TRANSIENT SHEET/CLOUD CAVITATING FLOWS

Studies are presented for a Clark-Y hydrofoil fixed at an attack angle of α=8° at a moderate Reynolds number, Re=7×10⁵, for both noncavitating and sheet/cloud cavitating conditions. The numerical simulations are performed via the commercial code CFX using a transport equation-based cavitation model, and the turbulence model utilizes the large eddy simulation (LES) approach with a classical eddy viscosity subgrid-scale turbulence model. The results show that numerical predictions are capable of capturing the initiation of the cavity, growth toward the trailing edge, and subsequent shedding, in accordance with the quantitative features observed in the experiment. The primary frequency, St =0.85, of the hydrodynamic fluctuations can be observed for noncavitation. It is induced by the shedding of the vortex structures at the trailing edge of the hydrofoil. The primary frequency, St =0.34, of the hydrodynamic fluctuations is induced by the growing up and shedding of the cavity, which can be observed for sheet/cloud cavitation. At the same time, some medium amplitude peaks are observed ranking from St =0.5 to St =1.5. These are due to the divergence influences from cavitation in different phases. These influences may lead to changes of vortex shedding frequencies at the trailing edge of the hydrofoil.