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In the maritime industry, cavitation erosion prediction becomes more and more critical, as the requirements for more efficient propellers increase. Model testing is yet the most typical way a propeller designer can, nowadays, get an estimation of the erosion risk on the propeller blades. However, cavitation erosion prediction using computational fluid dynamics (CFD) can possibly provide more information than a model test. In the present work, we review erosion risk models that can be used in conjunction with a multiphase unsteady Reynolds‐averaged Navier–Stokes (URANS) solver. Three different approaches have been evaluated, and we conclude that the energy balance approach, where it is assumed that the potential energy contained in a vapor structure is proportional to the volume of the structure, and the pressure difference between the surrounding pressure and the pressure within the structure, provides the best framework for erosion risk assessment. Based on this framework, the model used in this study is tested on the Delft Twist 11 hydrofoil, using a URANS method, and is validated against experimental observations. The predicted impact distribution agrees well with the damage pattern obtained from paint test. The model shows great potential for future use. Nevertheless, it should further be validated against full scale data, followed by an extended investigation on the effect of the driving pressure that leads to the collapse.

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Equations for thrust calculation of ducted propellers and waterjet propulsion systems are derived from the theory of open propellers. The streamtube of an open propeller shows contraction upstream and downstream of the propeller, with a strength depending on the propeller loading. The contraction of the streamtube in a waterjet propulsion unit is governed by the geometry of the installation. This paper presents the analyses of the development of the streamtube of a waterjet and a ducted propeller. Determination and visualization of the streamtubes is accomplished with a commercial CFD method. Development of the streamtube is analyzed in streamwise direction and as a function of the loading of the waterjet or the ducted propeller. It is proven that the ducted propeller has a fixed ratio between the velocity through the nozzle and the velocity downstream. This is comparable to the behavior of a waterjet, and consequently different from an open propeller. Thrust of the propulsion unit can be determined from a direct summation of all wall forces or from summation of the different terms of a momentum balance. The pressure, which acts on the streamtube surface, is neglected in this calculation, according to generally accepted theory. Comparison of both methods shows deviations for some operating conditions, which is attributed to the neglect of the pressure forces. It is concluded that the pressure forces on the streamtube of both ducted propellers and waterjet propulsion systems should not be neglected a priori.