Numerical characterisation of outboard dynamic-inlet waterjets: propulsive aspects of intake/pump integration

This study introduces the numerical model of the outboard dynamic-inlet waterjet (ODW), a novel concept in waterjet propulsion. The ODW consists of an axisymmetric nacelle housing an axial-flow pump and offering the unique advantage of being analysed independently of the target vessel. Addressing the gap in current literature, this paper presents a potential design study for the ODW under installed conditions integrating existing models of a hydrodynamic diffuser inlet together with a propulsive pump. Exploiting the symmetry of the propulsor, a single-channel configuration of the pump/intake installation is modelled. Steady Reynolds-averaged Navier–Stokes (RANS) system of equations is solved, closed by the \(k-\omega \) $k-\omega$ SST for turbulence and Zwart model for cavitation, respectively. Hydraulic and propulsive maps are generated with progressively increasing far-field velocities at three rotor speeds: 800, 1400, and 2000 rpm. Results reveal that under near nominal conditions, the pump performs similarly to its isolated operations. Integrated with the inlet, it achieves a propulsive efficiency of 0.77 at the highest rotor speed. Conversely, at low advancing speeds, local dynamics near the diffuser throat are found to be a source of possible cavitation issues, obstructing the stream tube and potentially leading to critical conditions.