• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1005-1012
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• 2011

The purpose of this study was to investigate the internal nozzle flow and cavitation characteristics numerically in both circular and elliptical nozzles. The program FLUENT 6.2 was used to perform the numerical simulation of the cavitating flow in the nozzles. A comparison was made between the cavitation shapes predicted numerically and those found experimentally in order to validate the numerical solution. This study showed that the cavitation in the circular nozzle had a cylindrical shape that was symmetrical with the nozzle axis. However, the cavitation in the elliptical nozzles had a horseshoe-like shape. In addition, the radial velocity distribution varied between the major and the minor axis planes when the working fluid was flowing into the inlet.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1361-1369
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• 2013

This study performs a computational fluid dynamics (CFD) analysis of the inner flow of a multihole injector nozzle by using ANSYS CFX 13.0. Based on the obtained results, a design of experiment (DOE) was performed and applied to investigate the effects of injector nozzle design parameters on cavitation. To analyze the design sensitivity and signal-to-noise ratio (S/N ratio), the hole diameter, hole length, hole angle, and K-factor of the nozzle hole were selected as design parameters, and the effect of these parameters was investigated at 16 experimental points. Consequently, it was found that the effect of the K-factor on the cavitation and inner flow of the injector nozzle is the greatest. Thus, the selection of a suitable K-factor is important in nozzle design considering cavitation flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.320-324
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• 2017

Effect of elliptical orifice on the spray characteristics of liquid jet ejecting into subsonic crossflows were experimentally studied. Circular/elliptical plain-orifice injectors, which had different ratios of the orifice length to diameter and major axis to minor axis, were used for transverse injection. Compared with the previous research, breakup lengths of elliptical nozzles are shorter than circular nozzles at all experimental condition. Cavitation/hydraulic flip are considered as a reduction in the breakup length at all circular/elliptical nozzle. In the case of liquid column trajectories, major axis which was placed to the crossflows, increases the frontal area of the liquid column exposed to the crossflows. Hence, the aerodynamic force exerted on the jet is increased and the penetration depth is reduced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.10
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• pp.933-939
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• 2010

The purpose of this study is to investigate the generation and development of cavitation in circular and elliptical nozzles. In order to investigate the influence of cavitation, the experiment was conducted with a set of elliptical nozzles that had the same cross-sectional area, different orifice aspect ratios (a/b). Each nozzle was made of acrylic so that visualization was possible. With the injection pressure, the internal flow of the nozzle was classified into the no-cavitation, cavitation, and hydraulic-flip regions. Regardless of the nozzle geometry, with the injection pressure, the flow rate in the no-cavitation and cavitation regions increased and the discharge coefficient decreased. However, the flow rate was constant in the hydraulic-flip region. In the elliptical nozzles, the generation and development of cavitation occurred at higher cavitation number than that in the case of a circular nozzle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.3 s.258
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• pp.264-272
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• 2007

The aim of this study is to investigate the effects of nozzle orifice shapes and the nozzle length-to-diameter ratio(L/D) on the nozzle cavitation formation inside the orifice and the external flow pattern. The nozzle used in this work was tested the taper orifice nozzle and the rectangular orifice nozzle which was made from the transparent acrylic acid resin. For studying the effect of the nozzle L/D ratio, it was used to three L/D ratios of 3.33, 10, and 20. The cavitation flow of nozzle was visualized by using the ICCD camera and optical system. This work revealed that the flow rate and discharge coefficient($C_d$) of the taper orifice nozzle was larger than those of the rectangular orifice nozzle at the same injection pressure. The cavitation flow was observed in the nozzle orifice at the low injection pressure and the breakup of liquid jet was promoted as the L/D ratio is decreased. The cavitation of biodiesel fuel was formed at the lower injection pressure than that of diesel fuel because of higher viscosity and density.

• Journal of ILASS-Korea
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• v.13 no.4
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• pp.200-205
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• 2008

Spray formation mechanism was controlled by a cavitation inside an injection nozzle. Nozzle geometry affects spray characteristics and formation behavior, which could determine engine performance and pollutant formation. A study was carried out on the influence of aspect ratio on cavitation inside a nozzle. The cavitation model available in Star-CD code was used to obtain cavitation behavior inside nozzle, which was compared with previous experimental results. In this paper, a CFD approach combining multiphase Volume-of-Fluid(VOF) and k-model was applied. The numerical results are similar with the experimental results.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.94-100
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• 2007

The purpose of this work is to investigate the effect of properties of diesel and biodiesel fuels on the nozzle cavitation and the effect of the length/diameter(L/D) ratio on internal and external flow pattern of nozzle at the various injection conditions. In order to study the effect of the L/D ratio on the nozzle cavitation characteristics of diesel and biodiesel, the characteristics of cavitation flow in the nozzle are visualized and analyzed at the injection pressure of 0.1 MPa to 0.7 MPa by using the visualized images. It was founded that the cavitation was formed in the nozzle orifice at the low injection pressure and the breakup of the issuing liquid jet was promoted at the low L/D ratio. When the L/D ratio decrease, cavitation beginning and growth were affect by cavitation number and Reynolds number.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.6
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• pp.108-116
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• 2013

Diesel engine injector is used for spraying the fuel into the cylinder chamber. Complex phenomenon like cavitation occurs from small scale domain, highly pressurized condition and rapid injection. Flow inside the nozzle affects the whole engine performance including combustion and exhaust, therefore understanding the flow inside the injector nozzle is very important. In this paper, cylindrical and convergent-divergent nozzles are suggested for nozzle types and their influences on nozzle internal flow and nozzle outlet characteristics will be analyzed by changing their outlet diameters.

• Journal of ILASS-Korea
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• v.9 no.4
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• pp.38-45
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• 2004

This study describes the analysis results of unsteady cavitating flows behavior inside nozzle of the prototype piezo-driven injector. This piezo-driven injector has been recognised as one of the next generation diesel injector due to a higher driven efficiency than the conventional solenoid-driven injector. The three dimensional geometry model along the central cross-section regarding of one injection hole has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. We could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.41-49
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• 1999

A feasibility study is performed for practical application of a Ventilating Water-Jet(VWJ) propulsor which attracts new attention as a candidate propulsor for super-high speed vessels. Super-cavitating foil sections are adopted for the rotor blades since the rotor is operating at ventilating condition. Wedge type and cavitator type foil sections are used for the design of rotor blades. Other geometric characteristics of rotors are selected from the Kaplan type ducted propeller rotors. The test section of KRISO cavitation tunnel is modified to perform open-water tests of the VWJ propulsors. The tests are performed both at fully-submerged and free-jet conditions. Ventilation occurred at the free-jet condition by sucking the air in the downstream side of the rotor, which easily develops as super-cavitation when the rotor operates at lower advance coefficients. Spoilers are attached at the trailing end of the pressure side of the blade section, in order to increase the lift force.