• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.966-972
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• 2010

Damping characteristics of a Helmholtz resonator to passively control the combustion instability were investigated by linear acoustic analysis and atmospheric acoustic tests. Its orifice length and diameter were selected as the design parameters and supplied SPL(sound pressure level) effect on damping characteristics were investigated. Damping capacity is improved by decreasing the orifice length as well as by increasing the orifice diameter. Also, the results showed that the damping capacity of the resonator decreased nonlinearly about above 110 dB and instabilities in the nonlinear region were more effectively suppressed by increasing the orifice diameter.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.695-702
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• 2008

Flow instability in the rocket turbo pump systems can be caused by various elements such as valve, orifice and venturi and etc. The formation of cavitation specially in the propellant feeding system can trigger the mass flow and pressure oscillation due to cyclic formation and depletion of cavitations. If the cryogenic propellant are used, which is very sensitive to temperature variation, the change of propellant properties due to thermodynamic effect should be accounted for in the flow analysis. This study focuses on the formation of cryogenic cavitation adopting MUSHY IDM model suggested by Shyy and coworkers. Also, the flow instability is investigated with developed numerical code in the downstream of orifice flow. To this end, three different orifices are selected and investigated by the numerical calculation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.50-55
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• 2015

This study examined the relationship between the shape of the inside of the PRV and the cavitation of the water supply system of an apartment house. In this paper, nine types of PRV with different gaps and shapes were analyzed numerically using a 3D model embedded in the commercial code, ANSYS-CFX. The lowest pressure and the maximum velocity occurred at the narrow gap, which is located at the between the stem and the disk. When the gap size was increased, the vapor volume fraction was always greater than 0, but the vapor volume fraction of the type of expansion pipe approached 0. These results indicate that the cavitation of PRV can be reduced by a shape change to the type of expansion pipe.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.1
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• pp.58-64
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• 2014

Hydraulic dual chamber, as the simulator for a dual pulse rocket motor, was tested by a high pressure device with various orifice-hole size being applied. Pressure difference occurs between 1st chamber and 2nd chamber depending on area ratio of the orifice to nozzle throat. Studying a design configuration of the orifice is essential to the motor development because pressure difference severely affects the rocket motor performance. It is noticed in this study that energy dissipation is caused by the vortex flow originating from the orifice as the 2nd chamber is operated. The flow field is simulated by a commercial computational fluid dynamics program, ANSYS FLUENT V14.5.

• 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.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.440-445
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• 2002

공압쿠션실린더(${\psi}80{\times}500^{st}$)의 쿠션장치인 쿠션슬리브(${\psi}20{\times}28^{st}$) 4종(Model #a, Model #b, Model #c, Model #d) 모델을 제작하여 수직하강하는 실린더에 각각 장착한 후, 각 모델에 따라 압력과 부하 특성을 비교하였다. 동일한 실험조건인 공급압력($5kg_{f}/$\textrm{cm}^2$)과 부하하중($70kg_{f}$)에서 각 모델별 실험을 실행하였다. 각 모델별 실험에서, Model #c의 쿠션슬리브인 경우가 가장 적합한 형상임을 알 수 있었다.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.5
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• pp.19-28
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• 2017

Effects of cavitation and hydraulic flip in circular and elliptical nozzles on the flow characteristics have been studied. Spray tests were conducted using injectors with different ratios of an orifice length(L) to a diameter(d) and of a major axis diameter(a) to a minor axis diameter(b). With the increment of an injection pressure drop, discharge coefficients slightly decreased in cavitation flows, and those suddenly dropped and were almost constant in hydraulic flip flows. For elliptical nozzles with L/b > 8 and L/a < 8, discharge coefficients and flow patterns showed different results from those in previous circular nozzles. When a flow in the elliptical nozzle was under steady condition, as the liquid column went downstream from the nozzle, its spray angle a little decreased in the plane of a major axis and increased in the plane of a minor axis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.73-76
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• 2006

Acoustic cavity as a stabilization device to control high-frequency combustion instabilities in liquid rocket engine is adopted and its damping capacity is verified in atmospheric temperature. Geometric effects of acoustic cavity on damping characteristics are analyzed and compared quantitatively. Satisfactory agreements have been achieved with linear acoustic analysis and experimental approach. Results show that the acoustic cavity of the largest orifice area or the shortest orifice length was the most effective in acoustic damping of the harmful resonant frequency finally, it is proved that an optimal design process is indispensable for the effective control of combustion instabilities.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.438-444
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• 2010

The spray characteristics of jet in crossflow (JICF) to improve the atomization and mixing characteristics of liquid Jet, while minimizing the impact on crossflow, were studied experimentally. By varying the temperature, velocity, pressure of crossflow and the speed, pressure of liquid Jet, the spray boundary (outer boundary, inner boundary) with the change of crossflow and liquid jet momentum ratio (q) were measured and led the experimental formula, compared with the results of previous work. Specifically, when the jet penetration with the shape of injector were measured, in the case of dual orifice Injector, under the influence of front orifice, the jet penetration of back orifice was improved approximately 18% ($L_h$ = 4 mm), compared with single orifice injector.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.6
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• pp.1067-1072
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• 2011

If the flow of booster gas which is exhausted to the rear part of a canister is properly restricted in the canister of a hot-launch system, the resultant pressure built up in the canister provides additional force to accelerate the missile to a required launch velocity. These thrust augmentation performances can be controlled through the configuration design of baseplate orifices. In this paper, the simple technique to analyze the thrust augmentation performances of baseplate orifices is suggested and the thrust augmentation characteristics by its various configurations are compared. According to the initial displacement of a missile, the inner pressure of a canister is measured from scaled cold flow tests, and the discharge coefficient of baseplate orifices is calculated. Then the thrust augmentation in a canister is simulated by applying these discharge characteristics to the AMESIM software for launch dynamics.