• Journal of the Korean Society of Visualization
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• v.19 no.2
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• pp.48-55
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• 2021

In order to design a propeller with high efficiency and excellent cavitation performance, theoretical and experimental studies on the cavitation and noise characteristics according to the blade section shape are essential. In general, sheet cavitation, bubble cavitation, and cloud cavitation are the main causes of hull vibration and propeller surface erosion. However vortex cavitation, which has the greatest influence on the noise level because the fastest CIS in ship propeller, has been researched for a long time and studies have been conducted recently to control it. In this experiment, the development process of cavitation was measured by using three dimensional wings with two different wing section and wing tip shapes, and the noise level at that time was evaluated. In addition, we evaluated the relationship between cavitation inception and hydrodynamic force using three component load cell and we measured the velocity field of wing wake using LDV.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.233-242
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• 2023

In this paper, the effect of mass injection on the control of tip vortex cavitation was studied experimentally. A mass injection system for a 3D hydrofoil was designed to control the location of injection as well as the injection rate. A series of cavitation tests were carried out in a cavitation tunnel for different injection locations and rates. The cavitation behaviour was observed using a high-speed camera and the corresponding noise was measured using a hydrophone installed in the observation window. The results showed that the tip vortex cavitation was suppressed under certain conditions and the noise was reduced in some frequency bands. It was also found that there is a location where the effect of mass injection could be maximized and hence the noise reduction.

• Ocean Systems Engineering
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• v.5 no.2
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• pp.125-138
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• 2015

In this study, hydrodynamic performance of a 400 mm diameter horizontal axis marine current turbine model was tested in a cavitation tunnel with 1.21 m x 0.8 m cross-section for over a range of tip speed ratios. Torque and thrust data, as well as cavitation visualizations, for certain operating conditions were acquired. Experimental results indicated that the turbine can be exposed to significant amount of sheet and cloud cavitation over the blades along with vortex cavitation at the blade tips. Inception and distribution of cavitation along the blades of the model turbine were then modelled numerically for design operating conditions using a vortex lattice method. The method was also applied to a turbine tested previously and obtained results were compared with the data available. The comparison between simulation results and experimental data showed a slight difference in terms of span-wise extent of the cavitation region. The cloud and tip vortex cavity observed in experiments cannot be modelled due to the fact that the VLM lacks the ability to predict such types of cavitation. Notwithstanding, the use of such prediction methods can provide a reasonably accurate approach to estimate, therefore take the hydrodynamic effects of cavitation into account in design and analysis of marine current turbines.

• Journal of Ocean Engineering and Technology
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• v.32 no.4
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• pp.244-252
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• 2018

This paper provides quantification of the effects of the turbulence model and grid refinement on the analysis of tip vortex flows by using the RANS(Reynolds averaged Navier-Stokes) method. Numerical simulations of the tip vortex flows of the NACA $66_2$-415 elliptic hydrofoil were conducted, and two turbulence models for RANS closure were tested, i.e., the Realizable $k-{\varepsilon}$ model and the Reynolds stress transport model. Numerical results were compared with available experimental data, and it was shown that the data for the Reynolds stress transport model that were computed on the finest grid system had better agreement in reproducing the development and propagation of the tip vortex. The Realizable $k-{\varepsilon}$ model overestimated the turbulence level in the vortex core and showed a diffusive behavior of the tip vortex. The tip vortex cavitation on the hydrofoil and its trajectory also showed good agreement between the current numerical results that were obtained using the Reynolds stress transport model and the results observed in the experiment.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.94-103
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• 1993

This study deals with an investigation on the tip vortex generated by an elliptic wing with section shapes of NACA 0020. The flow structure on the wing surface is investigated by using tufts test as well as observing the cavitation pattern. The surface pressure on a foil surface is measured to complement the visualized flow field. Results show that a strong spanwise pressure gradient is a definite contributor on the formation of tip vorex, and the fluids from both sides contribute to the evolutionary process of tip vortex. On the other hand, a series of experiments are conducted to investigate the detailed structure of tip-vortex at various angles of attack. The tip-vortex formation and development are observed by producing a cavitation, and then by a laser sheet technique in conduction with a dye injection method. The shape of tip-vortex and the distance between a vortex core and the trailing vortex sheet are found to vary with the angle of attack. Overall features of tip flow are evaluated to complement the vortex model based on inviscid theory.

• Journal of Ship and Ocean Technology
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• v.1 no.2
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• pp.19-30
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• 1997

The accurate prediction of the flow and the pressure distribution near the tip of the blade is crucial in determining the tip vortex cavitation inception which usually occurs on the blade tip or inside the core of the tip vortex just downstream of the blade tip. An improved boundary element method is applied to the prediction of the flow around propeller blades, with emphasis at the tip region. In the method, the Blow adapted grid and a higher order panel method, which combines a hyperboloidal panel geometry with a hi-quadratic dipole distribution, are used in order to accurately model the trailing wake geometry and the highly rolled-up regions in the wake. The method is applied to several propeller geometries and the results have been found to agree well to the existing experimental data. Inviscid flow methods are able to predict the pressures at the tip as well as the shape of the trailing wake. On the other hand, they are unable to determine the flow inside the viscous core of the tip vortex, where cavitation inception often occurs. Thus, a method is presented that treats the flow inside the viscous core. The inner flow is treated with a 2-D Clavier-stokes solution without making any assumptions for axisymmetric flow and conicity of the flow along the tip trajectory. The method can thus allow the treatment of general propeller blade configurations. The velocity and pressure distributions inside the core are shown and compared to those from other numerical methods.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.18-28
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• 2008

Fins are widely used for roll stabilization of passenger ferries and high performance naval ships, among others. In the present study, numerical simulations are performed to investigate the influence of end-plates upon the cavitation characteristics of a stabilizer fin for various angles of attack and speeds and the results are verified through a series of model experiments. It is found that a considerable retardation in tip vortex cavitation can be achieved with attachment of end-plates at the tip of the stabilizer fin. The results can be utilized for the design of stabilizer fins as well as the development of high performance control devices for ships.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.307-317
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• 2018

In this study, numerical investigations of the tip clearance flow characteristics of a pumpjet propulsor based on Computational Fluid Dynamics (CFD) method have been presented. The Zwart-Gerber-Belamri (Z-G-B) cavitation model based on Reynolds Averaged Navier-Stokes (RANS) method is employed. The structured gird is applied. The formation and development of the tip clearance flows has been investigated and presented. The structure of the tip leakage vortex has been shown. The radial distributions of different velocity components with different Span along the axial direction have been carried out to present the influence of the tip clearance flow on the main flow. In addition, the influences of the tip clearance size on the pumpjet propulsor performance, including the impact on the velocity flow fields and the cavitation characteristic, have been presented.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.111-118
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• 2007

In order to investigate the noise characteristics of the different caviation, noise measurements were carried out in a large cavitation tunnel of the Samsuug Ship Model Basin(SSMB). The noise measurements for a 3-dimensional hydrofoil were carried out at the angle of attack of $12^{\circ}$ and $16^{\circ}$ according to the decrease in cavitation number. It is exhibited that sound pressure level(SPL) increased sharply with cavitation inception. The frequency of the noise induced by sheet cavitation was higher than that of tip vortex cavitation in the phase of cavitation inception. Within the range of the high frequency, in the case of fully developed cavitation, sheet cavitation noise was significantly increased in sound pressure level compared with tip vortex cavitation noise. In this study, the noise characteristics of the different cavitation types were considered experimentally and would be utilized as a basis for the analysis of propeller cavitation noise.

• International Journal of Fluid Machinery and Systems
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• v.9 no.2
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• pp.160-168
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• 2016

In high speed turbopumps, cavitation occurs and often causes the flow instabilities such as cavitation surge and rotating cavitation. The occurrence of these cavitation instabilities is considered to relate to dynamic characteristics of the cavitation, which are modelled using a cavitation compliance and a mass flow gain factor. Various types of cavitation such as a blade surface cavitation, a tip leakage vortex cavitation, and a backflow vortex cavitation occur at the same time in the inducer and the dynamic characteristics of each cavitation have not been clarified yet in experiments. Focusing on the blade surface cavitation as one of fundamental cavitation, we investigated the dynamic characteristics of the blade surface cavitation on a flat plate hydrofoil in experiments in the present study.