Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

The Optimization Schemes of Waterjet Inlet Duct in Consideration of Pump Action
Hai Luo, Jiangming Ding*, Jiabing Jiang, Lingxun Li
School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology.
Wuhan, Hubei, China

the geometry of the inlet duct also affects the flow field around aft-hull,
as well as the pump ingestion condition. Wei et al. (2009) explored theeffect of duct inclination on the outflow uniformity, cavitation, flow
separation and applicability of variable working conditions. They
proposed that for ducts with different geometric structures in the same
application scenario, the flow characteristics inside the ducts may belarge different. Wu et al. (2015) designed the inlet duct with betterhydrodynamic performance by adjusting the inclination angle, lip radiusand shape, and slope radius of the inlet duct. Qian et al. (2017) compared
the difference of the flow field around stern of hull, which has inlet ductswith different inclination angles, and then proposed that optimizing theinclination angle of the inlet duct can improve the resistance performanceof waterjet ships. Therefore, the design of the inlet duct geometry is avery important task for the waterjet even the entire ship.

ABSTRACT
Based on the single inlet duct optimization scheme, and the weighting
function constructed by the hydrodynamic performance relationshipbetween the inlet duct and the waterjet, a more efficient optimization
scheme of the inlet duct in consideration of pump action is proposed. Theaccuracy and rationality of the proposed optimization scheme areverified by comparing the optimization results of different schemes,
numerical simulation and flow field analysis of the waterjet. In addition,according to the weighting function, the influence weights of theefficiency of inlet duct and the flow non-uniformity & perpendicularity
at duct outlet on the propulsion efficiency of the waterjet in this paper
are proposed respectively.

KEY WORDS: waterjet propulsion; inlet duct; numerical simulation;
optimization; propulsion efficiency.

In recent years, optimization methods have been often used in theresearch of the inlet duct geometry. The current inlet duct optimization
schemes can be divided into two types. The first optimization scheme(OptWJ) is to directly optimize the entire waterjet, where the entire
waterjet will be simulated using the CFD method and the overallhydrodynamic performance of the waterjet will be targeted foroptimization. In the study by Guo et al. (2020), a set of geometricallydifferent inlet ducts and nozzles were generated by changing the size of
7 design variables, and combined inlet ducts and nozzles with the samepump to form a set of complete waterjets. Then, taking the entire waterjet
as the numerical simulation object, and the propulsion efficiency of thewaterjet as the optimization target, the inlet duct and the nozzle with thebest propulsion efficiency was obtained. The optimization scheme issimple and direct in theory, and the optimization results are reliable.
However, due to the large number of components and the complex
structure of the waterjet, the computational cost is high and thus theoptimization efficiency is low.

INTRODUCTION
The inlet duct of the waterjet is an important hydraulic component
connecting the hull and the pump. The water sucked by the propulsion is
directed from the hull bottom through the inlet duct to the rotating pump
body. Approximately 7~9% of the total installed power was lost in theinlet duct (Verbeek and Bulten, 1999) and the flow in the inlet duct iscritical to this energy loss. Griffith-Jones (1994) found through windtunnel tests and numerical simulations that a separated flow region
consisting of low velocity, low energy recirculating fluid occurred on theroof the inlet duct around IVR=0.7. Roberts (1998) explored the effectof the hull boundary layer on the hydrodynamic performance of the inlet
duct through wind tunnel tests. Thicker boundary layers leading to more
extensive flow separation were found in his study. Park et al. (2005) usednumerical simulation to obtain the flow details inside the inlet duct of theflat waterjet, and compared it with the wind tunnel test results, and foundthat the two were in good agreement. In their research, the vortex inducedby the separation along the corner of the side wall of inlet was also clearlyshown.

The second optimization scheme (OptDuct) is to optimize the single inlet
duct, where only the inlet duct is simulated, and the pump is not includedin the computational domain. Therefore, this optimization scheme has
lower computational cost and faster optimization speed. In this scheme,
the hydrodynamic performance of the inlet duct is used as theoptimization target. In order to optimize the geometry of the inlet duct,

The flow inside the inlet duct is dominated by its own geometry. Further,3903