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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

Scale Effect Study and Real-Scale Calculation of the Wake Field of KCS
Hao Liu

Geng Chen

Hangzhou Applied Acoustics Research InstituteHangzhou, Zhejiang, China

Hangzhou Applied Acoustics Research InstituteHangzhou, Zhejiang, China

Sajun Guo

Song Nie

Hangzhou Applied Acoustics Research InstituteHangzhou, Zhejiang, China

Hangzhou Applied Acoustics Research InstituteHangzhou, Zhejiang, China

generated when the ship moves in the ideal fluid is the potential wake,
which is characterized by the fact that the farther away from the hull, thesmaller the value of the potential wake; because of the existence ofviscosity of the water, a boundary layer is formed on the surface of thehull during the movement of the ship, the water particle in the boundary
layer forms a friction wake at the forward velocity. Therefore, it can beseen that the friction wake near the hull should be the largest, and that
outwards along the hull should gradually decrease. The wake formed by
the wave-making action of the ship itself is called wave wake. Comparedwith the first two values, the wave wake value is generally smaller(Sheng Zhenbang, 2006). According to the above-mentioned causes of
wakes, the wake velocity u can be expressed as:𝑢 = 𝑢𝑓 + 𝑢𝑤 + 𝑢𝑝
(1)

ABSTRACTThe propeller propulsion efficiency is one of the key factors affecting therapidity of the ship, and the nominal wake field of the ship has animportant influence on the propulsion efficiency of the propeller (MiaoGuoping, 2009; He Yousheng, 1987; Day J, 1987). The difference of thenominal wake field on the propeller disk between the real scale and themodel scale (scale effect problem of the wake field) leads to the changeof the propeller propulsion efficiency along with a series of problems
such as cavitation, noise, and excitation [4-5] (Chu Shaowei, 2012; HanK, 2006). Therefore, it is of great significance to study the scale effect ofwake field for the rapidity of ships (Froude W, 1872; B.E Launder, 1972;
B.E Launder, 1974; Larsson L, 1991; Zhu Renchuan, 2007). Taking theKCS standard ship model as the research object, this paper calculates thewake field at a fixed posture based on the RANS method, including thenumerical simulation of the real ship at real scale, and comparison of thecalculated values and the internationally recognized experimental values,
to verify the accuracy of the numerical model. Without considering thewake field of free liquid surface and attitude change, the calculation in
ideal fluid and viscous fluid is carried out, and the potential wake fieldin ideal fluid and the coupling results of potential wake field andfrictional wake field under viscous action are obtained respectively, andthe results of the two are separated, to discuss the characteristics of thepotential wake field and the friction wake field and their effects on thepropeller respectively; the scale effect analysis of the friction wake field
is performed, including the circumferential distribution of the average
wake fraction and change rule of wake peak value, etc.

Where，𝑢𝑝 is the speed of the potential wake, 𝑢𝑓 is the speed of thefrictional wake, 𝑢𝑤 is the speed of the wave wake. Usually, the friction
wake accounts for a large proportion in the nominal wake field.
The main reason for the difference between wake field and wake fractionis that the Reynolds numbers of the ship model and the real ship aredifferent. According to the similarity theory, since we only satisfy
geometric similarity and Froude number similarity when conducting
model tests, the Reynolds number is different in order of magnitude.
Therefore, the boundary layer of the ship model is thicker than that of
the real ship, the friction wake fraction of the real ship is smaller thanthat of the ship model, and the scale effect of the friction wake is also themain factor in the scale effect of the wake field.
Since the wake field in an ideal fluid satisfies the similarity of the Froudenumber and isn’t affected by viscosity, the streamlines and wave-making
shapes near the ship model and the real ship are the same, so the potential
wake and wave wake have no scale effect; but in viscous fluids, if theinfluence of the existence of the boundary layer on the potential wakefield and the wave wake field is considered, the scale effect also has acertain influence on the two fields, which needs to be considered.

KEY WORDS: Scale effect, Real-scale, Potential wake field,Frictional wake field.

INTRODUCTION
When the ship sails forward at a certain speed in the water, the nearby
water is affected and flown by the hull, which is manifested as a current
accompanied around the hull, which is called wake. The wake field
behind the ship can be divided into potential wake, friction wake andwave wake according to the causes of formation. Among them, the wake

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