Numerical Investigations of Scale Effect on Cavitation Around Hydrofoils

Although scale effects on cavitation have been studied, there seems to be no experimental or numerical work has been done on scale effects on cavitation regimes for hydrofoils. The present study was motivated by the prediction uncertainty of cavitation performance in scaling an axial flow pump, which is also an indispensable step in the design and application of hydraulic machineries. Hydrofoil NACA66 was adopted in this paper to represent the general characteristics of hydrofoils. Three hydrofoils with similar boundary conditions were simulated and analyzed, i.e. the initial hydrofoil, the hydrofoil models scaled down 0.5 and 0.25 times, respectively. High quality hexahedral mesh was established based on three-dimensional geometry of the hydrofoils. The monitoring points were arranged at the same locations relative to the boundary in each case. Computations were conducted on these three-dimensional hydrofoils, based on Detached Eddy Simulation (DES) turbulence model and Zwart cavitation model, which is a homogeneous model of cavitation, considering vapor/water mixture as one phase. In order to validate the practicability of numerical method and configuration employed in this paper, the numerical calculation of the initial hydrofoil was compared with experimental results provided by previous researchers, including the evolution of cavitation and pressure fluctuation on suction surface of the hydrofoil. According to the comparisons of the simulation results of the initial case and the other two scaled down models, we found the boundary layer suppresses the reentrant jet, which plays a critical role in cavitation detachment. Consequently, it influences the evolution of cavitation from the initial bubble, sheet cavitation, cloud cavitation and bubble breakup. Meantime, cavity evolution, cavity lengths, as well as cloud shedding periods were analyzed and discussed.Copyright © 2014 by ASME