Energy conversion and performance analysis of the submerged waterjet relative to the conventional waterjet in self-propulsion

Artikel i vetenskaplig tidskrift, 2025

The submerged waterjet and conventional waterjet in self-propulsion exhibit significant discrepancies in energy and propulsion performances, but systematic exploration of the underlying mechanisms remains limited. This paper proposes a comprehensive analysis method to investigate energy conversion and utilization processes of hull-waterjet system. Supported by model tests, the energy conversion processes of two series model ships propelled by submerged waterjet (SubWS) and conventional waterjet (ConWS) are numerically investigated below semi-displacement speeds. SubWS achieves an overall propulsion efficiency around 67% across most operational conditions, while that of ConWS climbs from 50% to 62% at whole speed range. The shaft power of SubWS achieves 17.7%, 14.3% and 5.0% reduction compared to ConWS at low to high three typical speed conditions, proving its energy-saving potential in a wide speed range. Detailed explorations on energy performances are evaluated by system hydraulic efficiency, thrust generation efficiency and resistance overcome efficiency in turn. Firstly, the cases of submerged waterjet and conventional waterjet exhibits both excellent and highly similar hydraulic performances in self-propulsion. This work demonstrates that the distinguished differences between corresponding proportions of axial kinetic energy flux change to effective hydraulic power of ConWS and SubWS are one of the major reasons, accounting for the observed discrepancies of overall energy performance. Hull wake excitation efficiency remains above 1.0 for both systems, indicating flow distortion around hull enhances the energy performance of waterjet-hull system. Additionally, the waterjet suction significantly impacts resistance overcome efficiency due to hull pressure differences between bare hull and self-propulsion.