APPLICATION OF NUMERICAL METHODS TO STUDY THE EFFECTS OF CAVITATION ON THE HYDRODYNAMIC CHARACTERISTICS OF THE HYDROFOIL NACA 4412

Abstract

Cavitation is the phenomenon in which a liquid undergoes local vaporization in regions having pressure below the saturated vapor pressure. When the vapor bubbles are transported to regions of higher pressure, they collapse violently, generating intense pressure pulses that damage the surface of impeller blades, cause noise and vibration, and reduce the hydraulic efficiency of the machine during operation. For a hydrofoil, cavitation typically occurs on the suction side, at the leading edge, and at the trailing edge; it leads to a reduction in the lift coefficient, an increase in the drag coefficient, and induces fluctuations in the loads acting on it. Therefore, investigating the influence of cavitation on the hydrodynamic characteristics of a hydrofoil is of great importance for the design and performance prediction of hydraulic machinery blades operating efficiently under cavitating conditions. In this study, a computational fluid dynamics (CFD) approach is employed to investigate the effects of cavitation on the hydrodynamic performance of the hydrofoil NACA 4412. The full cavitation model coupled with the RNG k-ε turbulence model is used to simulate the formation, development, and collapse of cavitation bubbles occurring on the suction side, leading edge, and trailing edge of the hydrofoil NACA 4412. The simulation results indicate that the occurrence of cavitation significantly reduces the lift coefficient and increases the drag coefficient, while also causing large pressure fluctuations in the trailing-edge region of the hydrofoil. At the attack angle α = 15°, the lift coefficient C_l of the hydrofoil NACA 4412 decreases about 14%, whereas the drag coefficient C_d increases about 34%.