1 Department of Mechanical Engineering, Technical University of Denmark2 Coastal, Maritime and Structural Engineering, Department of Mechanical Engineering, Technical University of Denmark
Cavitation on marine propellers causes thrust breakdown, noise, vibration and erosion. The increasing demand for high-efficiency propellers makes it difficult to avoid the occurrence of cavitation. Currently, practical analysis of propeller cavitation depends on cavitation tunnel test, empirical criteria and inviscid flow method, but a series of model test is costly and the other two methods have low accuracy. Nowadays, computational fluid dynamics by using a viscous flow solver is common for practical industrial applications in many disciplines. Cavitation models in viscous flow solvers have been developed in the last decade. They show the potential for the simulation of propeller cavitation with robustness, but they are still to be more proved for practical applications. In the present work, hydrodynamic and numerical characteristics of several cavitation models developed for a viscous flow solver are investigated, and one of the cavitation models is verified for the cavitation simulation on marine propellers. Three cavitation models with a vapor transport equation and a cavitation model with a barotropic state law are implemented in the in-house RANS solver, EllipSys. The numerical results for cavitating flows on a 2D hydrofoil are compared with the experimental results. In the current implementation, three models with a vapor transport equation show numerical stability and equivalently good accuracy in simulating steady and unsteady sheet cavitation. More validations for cavitating flows on 3D hydrofoils and conventional/highly-skewed propellers are performed with one of three cavitation models proven in 2D analysis. 3D cases also show accuracy and robustness of numerical method in simulating steady and unsteady sheet cavitation on complicated geometries. Hydrodynamic characteristics of cavitation like lift/drag variation with respect to cavity extent, re-entrant jet at the cavity closure and periodic oscillation of the cavity closure are demonstrated in the numerical results. The cavitation simulations on propellers are performed in the open-water and behind-hull conditions. In the behind-hull condition, the wake field from a hull is applied to a plane upstream from the propeller by using the actuator disk model instead of modeling a whole hull. The computed cavity profile shows a reasonable agreement with the experimental result and the transient nature of propeller cavitation behind a hull is reproduced in the simulation. The overall results suggest the possibility of the cavitation model in the RANS solver to be used for practical applications in propeller design process as a complementary tool to the cavitation tunnel test and the other numerical methods. The outstanding issue for cloudy and vortex cavitation requires further improvement and validation.