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

Numerical Simulation and Experimental Verification of the Nozzle Flow of a Waterjet Model
Zhiyuan Zhang12, Gang Chen2, Jie Gong3, Chenjun Yang1
1Shanghai Jiao Tong University

Shanghai, China
2Marine Design & Research Institute of China

Shanghai, China
3Wuhan University of TechnologyWuhan, Hubei, China

ABSTRACTThe waterjet thrust is calculated usually according to the momentum
theorem by obtaining the momentum flux at the inlet and nozzle. Mostof the relevant studies focus on the inlet flow, but less on the nozzle flow.
The conventional method is to assume that the nozzle flow is uniform,
which is different from the actual situation and may affect the accuracyof waterjet thrust prediction. In this paper, A waterjet flow was
calculated by RANS method and verified by the experiment. Finally, thedifferences between the real flow profile and the conventional assumed
one are compared, and the influence on the nozzle momentum and thethrust are analyzed. According to the results, the axial momentum fluxof the non-uniform flow is greater than that of the uniform one.

KEY WORDS: Waterjet, Nozzle flow, Numerical simulation,
Experimental verification.

INTRODUCTION
It is important to calculate or measure the thrust for predicting thewaterjet performance. The 21st ITTC in 1996 recommended twomethods to measure the thrust of waterjet: momentum flux method anddirect thrust measurement method (Proceedings of the 21st ITTC, 1996).
The direct thrust measurement method is difficult to realize in theexperiment. Most research institutions used momentum flux method toobtain the thrust of waterjet. The so-called momentum flux method
regards the fluid flowing through the waterjet unit as a control volume.
The force on the control volume, that is the thrust of the waterjet unit, iscalculated according to the momentum theorem by obtaining themomentum flux at the inlet and nozzle. The conventional method is toassume that the nozzle flow uniform (Proceedings of the 23st ITTC, 2002),
and then calculate the nozzle momentum flux when the nozzle diameteris known. However, the jet flow is not uniform actually due to theinfluence of the nozzle profile, which will cause the difference between
the calculated momentum and the actual one, and further affect theprediction accuracy of waterjet thrust. Scherer, O. (2001) has used Laser
Doppler velocimetry to determine the momentum flux for calculating thethrust more accurately. Park, W.G. et al (2005) computed the jet velocities
just behind the nozzle and compared them with the experiment results. The3897

24th ITTC provided the jet velocity survey data by six research institutes.
The jet survey was measured with Laser Doppler, Pitot-static and 5-holeprobes. (Proceedings of the 24th ITTC, 2005). Jung, K.H. et al (2006)
measured velocity vector fields at the nozzle exit using stereoscopic PIV
measurements.
In this paper, the internal and external flow of a waterjet model wasnumerically simulated based on RANS equation. The free surface wasconsidered. The experiment about measuring of the nozzle flow of thewaterjet model was carried out in the Science and Technology on Water
Jet Propulsion Laboratory, Marine Design & Research Institute of China.
The pitot tube probe was used to measure the axial velocity at each radius
within the nozzle section. The numerical results were verified bycomparing with the experimental results. Finally, the differences
between the actual nozzle flow and the assumed uniform nozzle flow
were compared, and the influences on the nozzle momentum flux andthe thrust were analyzed.
According to the results, the numerical results are consistent with theexperimental results, and the actual nozzle momentum flux is greaterthan that calculated by the uniform nozzle flow assumption, whichcauses the actual thrust is greater than the uniform one. So, the waterjet
thrust predicted by the uniform nozzle flow assumption is moreconservative.

RESEARCH OBJECT
In this paper, a mixed-flow pump model was selected as the research
object to study the nozzle flow characteristics. The mixed-flow pumpmodel is composed of inlet duct, shaft, impeller, guide vane and nozzle.
The 3D model is illustrated in Fig. 1, and the characteristic diameter(inlet duct diameter before impeller) is 0.2m.

Fig. 1. The mixed-flow waterjet pump 3D model