• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.839-847
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• 2004

In this study, the flow characteristics within supersonic cascades are numerically investigated by using Fine Turbo, a commercial CFD code. Cascade flows are computed for three different inlet conditions. : a uniform supersonic inlet condition, a linear nozzle and a converging-diverging nozzle located in front of cascades. The effect of inlet conditions is compared and flow characteristics including shock patterns and shock-boundary layer interaction are analyzed. Also the effect of design parameters such as pitch-chord ratio, blade angle and blade surface curvature on the flow within supersonic cascades are studied.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.460-465
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• 2004

ESPR project started in 1999 with METI and NEDO support as five-years program in order to develop necessary technologies for the next-generation SST engine. In ESPR program, jet noise reduction technologies are focused as environmentally compatible technologies, which are critical to realize next-generation SST. In designing a lobed mixer nozzle which is a jet noise suppression system, there are many difficulties to understand the detailed flow phenomena occurred in the system because of its complexity. Large Eddy Simulation (LES) was applied to the lobed mixer nozzle flow analysis in ESPR project. The results demonstrated that LES approach was capable of predicting mixing characteristics of a complicated flow.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.357-361
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• 2010

When high-pressure gas is exhausted through nozzle exit to the atmosphere, expanded supersonic jet is formed with the Mach disk at a specific condition. In two-dimensional supersonic jets, the hysteresis phenomenon of the reflected shock waves is found to occur under quasi-steady flow conditions. Transitional pressure ratio between the regular reflection and Mach reflection in the jet is affected by this phenomenon. In the present study, experiments are carried out on internal flow in a supersonic nozzle to clarify the hysteresis phenomena for the shock waves and to discuss its interdependence on the rate of the change of pressure ratio with time. Flow visualization is carried out separately on the straight and divergent channels downstream of the nozzle throat section. The influence that the hysteresis phenomena have on the location of shock wave in a supersonic nozzle is also investigated experimentally.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.1048-1050
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• 2017

본 연구에는 핀틀 노즐의 열변형 영향을 평가하기 위해 단방향 유체-구조 연성해석을 수행하였다. 단방향 유체-구조 연성해석을 위해 핀틀-노즐의 내부에 발생하는 압력 및 온도분포를 유동해석을 통해 도출하였고, 압력 및 온도분포 값을 각각의 유체-구조 해석의 하중조건으로 적용하여 핀틀의 변형량을 확인하였다. 변형에 대한 추력특성 변화를 확인하기 위해 양방향 유체-구조 연성해석을 수행 중이다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.39-42
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• 2008

Alloy 718 nozzle component was manufactured by hot working and electron beam welding process. In this process, domestic 718 materials were applied and evaluated. Hot compression tests were carried out at a lot of process conditions and microstructural evaluation was investigated. Using the results, FEM simulations were performed in order to optimize the hot working process. After hot working, forged work-pieces were machined and welded by electron beam. Final nozzle component were heat treated and their microstructure and mechanical properties were investigated.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제23회 추계학술대회 논문집
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• pp.157-161
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• 2004

추력 1700kN을 생성하기 위한 액체로켓엔진을 구성함에 있어, 에너지 특성을 높이기 위하여 터빈을 구동시킨 고온의 산화제 과잉 연소가스가 연소실로 공급되는 close type으로 선정되었으며, 막냉각에 의한 연소가스 특성의 변화, 노즐의 형상에 의한 효율, 연소효율 등을 고려한 연소실 및 노즐설계가 수행되었다. 또한 노즐을 팽창하는 동안의 연소가스의 상태 변화와 가스 구성을 그래프로 살펴보았다

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.849-854
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• 2008

We have been developing a 1500N-thrust Swirling-Oxidizer-Flow-Type hybrid rocket engine. In order to put the engine into practical use, we conducted long duration burning experiments up to 25s to examine the influence of configuration change of fuel grain on the engine performance and designed an LOX vaporization nozzle to supply GOX for the 1500N-thrust engine. The experiment with a small hybrid rocket engine showed that combustion was stable and the engine performance was approximately constant during combustion. There was no essential problem to with increasing combustion time. The LOX vaporization nozzle designed had 30 rectangular channels with a depth of 0.5mm. During passing through the nozzle, the LOX increased in temperature and vaporized sufficiently.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.78-81
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• 2008

A numerical study of the unsteady flow in an over-expanded thrust optimized contour and compressed truncated perfect rocket nozzle is carried out in present paper. These rocket nozzles are subject to flow separation in transient phase at engine start-up and/or engine shut-down. The separation flow structures at different pressure ratios are observed. The start-up process exhibits two different shock structures such as FSS (Free Shock Separation) and RSS (Restricted Shock Separation). For a range of pressure ratios, hysteresis phenomenon occurs between these two separation patterns. A three-dimension compressible Navier-Stokes solver is used for the present study. One equation Spalart-Allmaras turbulence model is selected. The computed nozzle wall pressures show a good agreement with the experimental measurements. Present results have shown that present code can be used for the analysis of the transient flows in nozzle.

• 한국추진공학회지
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• 제23권6호
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• pp.1-10
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• 2019

노즐 내 파동은 노즐목을 빠져나가는 유동의 공력음향학적인 효과로 인해 연소불안정을 감쇠시키는 주요 요소 중 하나로 알려져 있다. 이와 같은 효과는 노즐 어드미턴스라는 지표를 통해 정량적으로 평가가 가능하다. 본 연구에서는 현재까지 로켓 연소불안정 억제에 가장 효과적인 노즐감쇠(nozzle damping)와 연계된 노즐 어드미턴스를 구하는 여러 기법을 소개한다. 이중, 가장 널리 알려진 1차원 선형 오일러 방정식을 도입하여 노즐의 주 설계 변수에 따른 노즐 어드미턴스의 경향을 분석하였다. 분석 결과, 노즐 수축부 길이가 짧아질수록 축방향 노즐 어드미턴스의 값이 낮게 나타나는 주파수 영역대가 확장되므로 짧은 노즐일수록 주파수 의존성을 줄인다는 기존 이론을 검증하였다. 또한, 짧은 노즐 이론을 통한 어드미턴스 예측은 1차 접선방향 압력 섭동에는 적합하지 않음을 알 수 있었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.165-172
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• 2004

LE-7A is the main engine of the H-IIA launch vehicle. Under its development, the nozzle suffered from two troubles during startup and shutdown transients of the engine. One is a large side load, which damages the actuator of the nozzle, and the other is damage on regenerative cooling tubes due to high heat load. It has been considered that these problems are caused by a peculiar separation pattern called Restricted Shock Separation (RSS). RSS is observed in several rocket nozzles, for example, LE-7A nozzle, Vulcain nozzle and so on. Their contours are not conventional truncated perfect (TP) nozzle - LE-7A nozzle is a compressed truncated perfect (CTP) nozzle and Vulcain nozzle is a thrust optimized (TO) nozzle. Although it is believed that the occurrence of RSS is affected by the nozzle contour, the mechanisms are not clarified sufficiently yet. In the present paper, a parametric numerical study is carried out to investigate the mechanisms of the occurrence of RSS in CTP nozzles during startup transient. The results show that RSS is caused by the adverse pressure gradient downstream of the Mach disk. The adverse pressure gradient is caused by the interaction of the pressure wave and Mach disk. The method to avoid the occurrence of RSS is also examined. A small step inside the nozzle affects the position of the separation point and prevents RSS. The result shows that the possibility that RSS can be suppressed by controlling the position of the separation point.