Analysis of waterjet-hull interaction and its impact on the propulsion performance of a four-waterjet-propelled ship

摘要

Waterjet-hull interaction has different effects on the propulsion performance of the outer and inner waterjets in ships propelled by four waterjets. The dead rise angle of the hull lines near the stern leads to different inflow characteristics in the capture areas of individual waterjets. To better understand these effects, self-propulsion tests were performed to investigate the thrust deduction fraction and energy/momentum velocity coefficients, and numerical simulations of unsteady multiphase flows were conducted using a discretised impeller/stator with dynamic overset grids. Results obtained indicate that the flow rates and gross thrust of inner waterjets were greater than those of the outer waterjets under the same rotational speeds, and that these differences gradually decreased with increases in the advanced speed. The hull had a stronger negative effect on the inflow of the outer waterjet because its energy/momentum velocity coefficients were smaller than those of the inner waterjets. Additionally, flow field analysis of the capture area verified the quality of the computations, and internal flow field analysis provided additional validation of observed results. It was found that the inlet-duct design and the presence of stabilizer fins caused different interaction behaviours, resulting in the propulsion performance discrepancies observed in four-waterjet systems.