Calibration of two-phase numerical models for the hydrodynamic characterization of Outboard Dynamic-inlet Waterjets

This study proposes numerical solutions for two-phase models applied to an Outboard Dynamic-inlet waterjet (ODW). The ODW consists of an axisymmetric nacelle housing an axial-flow pump for naval propulsion. It shows many advantages over a propeller; the very high efficiency of the waterjet pumps offers higher speeds for the same power or substantially lower fuel consumption at a constant speed with less power. However, phenomena such as cavitation are also present in this type of engine; its presence can lead to a reduction in efficiency and performance. The study, utilizing computational fluid dynamics (CFD), enables the prediction of this phenomenon's occurrence through the modeling of different approaches that ensure reliable predictions. The results are obtained using the Ansys Fluent computational fluid dynamics software. The simulations progress through three stages: first, a 2D model of the dynamic intake for direct comparison with experimental data, followed by a similar but three-dimensional intake geometry, and finally, a 3D model of the entire nacelle that isolates the processed fluid. Analysis of simplified geometries allows for the calibration of a computational model that is ultimately applied to the entire 3D geometry of the propulsor. Each component is tested under different operating conditions, in order to obtain a complete overview of all components that may be subject to cavitation; the results show how the behavior and efficiency of each of them is affected by the phenomenon. Ultimately, the performance of the complete waterjet—considering various nacelle geometries at different speeds—are presented and compared, without accounting for any potential phase change of the fluid. The work aims to provide a complete picture of how cavitation affects the entire propulsion system, although this is currently limited by the sofftware development stage.