Flow rectification and wake stabilization in a marine submerged waterjet: Energy-flux analysis under variable loading conditions

Unlike open propellers whose efficiency is tightly coupled to blade loading, the marine submerged waterjet (SWJ) achieves robust performance through a distinctive decoupling of hydraulic conversion and thrust generation across a wide range of operating conditions. This study investigates the underlying flow physics governing this mechanism over advance coefficients spanning J = 0.50–1.50, using the improved delayed detached eddy simulation method with validation against model tests. To clarify the evolution of energy gains and losses, a control-volume energy-flux method is developed to quantify the energy conversion process in the SWJ system. Quantitative results demonstrate that the complete rotor–stator–duct (RSD) configuration maintains a high overall energy efficiency within the range ηO = 0.657–0.693 across J = 1.00–1.50, substantially higher than the corresponding values of ηO = 0.500–0.603 for the isolated rotor R and ηO = 0.546–0.575 for the rotor–duct (RD) configuration over the same range of advance coefficients. This performance enhancement originates not solely from swirl recovery but also from an underlying wake stabilization mechanism. Specifically, at the design condition J = 1.25, the post-stator reduces the transverse kinetic energy flux ratio at the control-volume outlet from 15.3% in the RD configuration to 0.5% in the RSD system. This pre-conditioning deprives the downstream shear layer of the energy required to sustain large-scale coherent structures, thereby suppressing irreversible dissipation in the near-wake. Furthermore, under heavy-loading conditions, the duct functions as a physical confinement barrier that reduces the outer-pump energy loss ratio from 19.9% to 9.7% at J = 0.50, delaying the onset of jet-wake mixing losses. This synergistic control of the flow structure, achieved by stabilizing the shear layer internally and confining the jet externally, constitutes the distinctive hydrodynamic advantage of the SWJ and provides guidance for its design and optimization over broad operating envelopes.