• 대한기계학회논문집B
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• 제31권3호
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.288-293
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• 2001

This paper presents the water-hammer effect due to the rapid opening and closing of isolation valve and thruster valve in the spacecraft propulsion system. The single propellant feed system was modeled to investigate the maximum peak pressure due to the water-hammer effect. The test parameters are tank supply pressure, shape and throat length of orifice and line length. Kerosene was used as the inert simulant propellant liquid instead of hydrazine. As downstream line length after isolation valve increased from 1.5 to 2.5m, the maximum line-filling water-hammer peak pressure decreased, but the average time interval between peak pressures increased. The maximum line-filling water-hammer peak pressure with orifice was lower than without orifice, and the maximum line-filling water-hammer peak pressure with orifice at the back of isolation valve was lower than with orifice in front of isolation valve. Without orifice, the maximum water-hammer peak pressure due to the rapid opening and closing of the thruster valve was about 126% of tank supply pressure. With orifice, it decreased. As orifice throat length increased, it decreased. The maximum water-hammer peak pressure due to the rapid closing of the thruster valve with converging-diverging orifice was lower than normal orifice. It was found that the orifice as a means of pressure drop was very effective to reduce the water hammer peak pressure at the thruster valve. The results of this study can be used for the design of spacecraft liquid propulsion feed system.

• 한국추진공학회지
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• 제7권1호
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• pp.28-39
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• 2003

본 연구에서는 캐비테이션과 수력튀김과 같은 유동 현상이 수직 분사된 액체 제트의 분열에 미치는 영향을 살펴보았다. 오리피스 지름, 오리피스의 길이대 지름비, 오리피스 입구의 형상 그리고 배출 압력을 변화시켜가며 내부 유동 변화를 살피고 수직분사시 액주의 분열 거리와 제적을 구하여 기존의 연구 결과와 비교하고 분석하였다. 실험 결과 곡률이 없는 경우(sharp edged)의 오리피스에서는 어느 정도 이상의 압력에서 모두 캐비테이션이 발생하였고 곡률이 없는 경우 중 길이대 지름비가 작은 오리피스에선 캐비테이션 성장에 의한 수력튀김(hydraulic flip)현상도 관찰할 수 있었다 수직분사시 캐비테이션이 성장할수록 그리고 수력튀김 현상이 나타날 때 액주의 분열거리는 상당히 감소한다는 것을 알 수 있었다. 하지만 곡률이 있는 경우와 없는 경우 모두 유량 계수를 고려한 유효지름과 유효 모멘텀 플럭스 비에 대해 거의 같은 궤적 형상을 나타낸다는 것을 알 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.357-360
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• 2002

The effect of distance between ninety degree elbow close to upstream face of orifice plate and orifice plate on discharge coefficient was investigated. The distributions of discharge coefficient and differential pressure caused by elbow and short upstream straight length were examined and modified discharge coefficient was introduced. The results presented in this study could be useful when orifice plate is installed under the condition of simple flow disturbance element and short upstream straight length.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.79-82
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• 2002

Three-dimensional pipe flows with elbows and tees for few different pipe fittings are calculated to estimate the effect of swirling flow on measuring accuracy of orifice flow meter. It is evaluated how the pressure difference across the orifice is dependent on the length of upstream straight pipe in a branch and how swirl intensity, swirl angel and axial velocity distribution affect the measuring error of orifice flowmeter. From the results, it is found that, regardless of flow rate specified in this calculation, the effect of the straight pipe length can be neglected for the lengths larger than thirty diameters although there still remain significant swirl at the orifice

• 설비공학논문집
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• 제18권2호
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• pp.186-191
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• 2006

In this study, five experiments were carried out, with an orifice located downstream of a fan in case I where upstream duct length is 6 D, and that in the downstream is 4 D and different downstream distance to the fan in the rest, so as to determine the optimal location of the orifice and reduce the duct length of airflow measurement device. The resulting flow rate-pressure drop correlations were found to satisfy the limitation of SMACNA standard, which specified an error of $\pm7.5\%$ based on the real flow rate. Also, the best one of five. cases was achieved with the orifice located midway of the orifice duct four times its diameter long.

• 한국분무공학회지
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• 제7권4호
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• pp.32-41
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• 2002

The breakup characteristics of liquid sheets formed by like-doublet injector were investigated in the cold-flow and atmospheric ambient pressure condition. The sheet breakup wavelength, which induces the sheet to be broken into ligaments, as well as the sheet breakup length, which is important for the flame location, was measured using a stroboscopic light. The liquid ligaments are formed intermittently after the breakup of sheet, and the wavelength of ligaments has been believed to have a relation to the combustion instability of liquid rocket engine. Therefore, the wavelength of ligaments and the breakup length of ligaments into fine drops were also measured. Since these spray characteristics are affected by the flow characteristics of two liquid jets before they impinge on each other, we focused on the effects of orifice internal flow such as the cavitation phenomenon that occurs inside the sharp-edged orifice. From the experimental results, we found that the liquid jet turbulence delays the sheet breakup and makes shorter wavelengths for both sheets and ligaments. Since the turbulent strength of sharp-edged orifice is stronger than that of round-edged orifice, the shape of orifice entrance results in large differences in the spray characteristics. Using these results, we proposed empirical models on the spray characteristics of the like-doublet injector, and these models are believed to provide some useful and actual data for designing liquid rocket combustors.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.72-75
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• 2003

본 연구에서는 인젝터 형상에 따른 캐비테이션과 같은 유동 현상이 수직 분사된 액체 제트의 분열에 미치는 영향을 살펴보고자 하였다. 오리피스의 지름과 길이대 지름비(L/d) 및 입구의 형상이 다른 인젝터에서 압력을 변화시켜가며 내부 유동 변화를 살피고 수직분사 시 액주의 분열 거리와 궤적을 구하여 기존의 연구 결과와 비교하고 분석하였다. 실험 결과 곡률이 없는 경우(sharp edged)의 오리피스에서는 어느 정도 이상의 압력에서 모두 캐비테이션이 발생하였고 곡률이 없는 경우 중 길이대 지름비가 작은 오리피스에선 더 높은 압력에서 캐비테이션 성장에 의한 수력튀김(hydraulic flip)현상도 관찰할 수 있었다. 수직분사 시 곡률이 있는 경우와 없는 경우 모두 동일한 모멘텀 플럭스 비(q)에 대해 거의 같은 궤적 형상을 보였으나 캐비테이션이 일어날 경우 교란에 의해 액주의 분열 거리는 감소하였고 수력튀김 또한 제트 단면적의 감소 및 제트의 확산으로 분열거리가 감소하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
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• pp.36-39
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• 2008

연소 불안정 현상은 액체로켓엔진 개발과정에 있어서 반드시 해결해야 하는 문제이다. 이것을 억제하기 위한 도구 중의 하나인 음향공의 오리피스 길이 변화에 의한 감쇠 효과를 선형 음향 해석과 실험을 통하여 연구하였다. 오리피스의 길이가 짧아질수록 감쇠효과가 증가하는 것을 확인하였으며 실험과 선형 음향 해석 결과가 서로 동일한 경향을 보이는 것을 확인 하였다. 또한, 가진 음원의 크기에 따른 실험을 수행하였는데 그 결과 오리피스 길이와 단면적이 작아질수록 가진 음원의 크기 증가의 따른 비선형성이 증가하는 것을 확인하였다.

• 한국분무공학회지
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• 제6권2호
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• pp.9-15
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• 2001

The internal flow characteristics of a gasoline direct injector have been studied to improve fuel economy and reduce exhaust emissions. Computational Fluid Dynamics (CFD) is used to examine the internal flow of the GDI with the purpose of designing the optimum geometry of the injector. This study tests orifice length, cone angle, swirl angle, orifice diameter and needle lift. The results show that optimum sizes of the orifice length, cone angle, swirl angle, orifice diameter and needle lift are 0.8mm, $140^{\circ},\;120^{\circ},\;80mm\;and\;70{\mu}m$, respectively. The size of the lift does not affect the formation of the air core signficantly near the tip of the needle compared to the ball-type needle. The vena contracta phenomenon near the orifice inlet can be released by smoothing the edge.