• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.297-301
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• 2007

초음속 충동형 터빈과 같이 종횡비가 작은 경우 로터 익형은 반경방향으로 동일한 단면을 갖는 형태로 구현된다. 이 경우 터빈 로터는 터빈 동익의 프로파일 직경에 따라 설계에서 의도하지 않은 유로면적분포와 터빈 성능의 차이를 보인다. 본 연구에서는 터빈 동익 프로파일을 정의하는 직경이 터빈 성능에 미치는 영향을 고찰하기 위하여 3개의 다른 위치에서 정의된 터빈 로터에 대한 유동해석을 수행하고 결과를 고찰하였다. 계산 결과 팁에서 단면이 정의된 경우 설계에서 의도한 유로면적 변화를 보이며 다른 프로파일 직경에서 정의된 터빈에 비해 우수한 성능을 보임을 확인하였다.

• 대한기계학회논문집B
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• 제24권8호
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• pp.1128-1138
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• 2000

Pumping action in ejector systems is generally achieved through the mixing of a high-velocity and high-energy stream with a lower-velocity and lower-energy stream within a duct. The design and performance evaluation of the ejector systems has developed as a combination of scale-model experiments, empiricism and theoretical analyses applicable only to very simplified configurations, because of the generic complexity of the flow phenomena. In order to predict the detailed performance characteristics of such systems, the flow phenomena throughout the operating regimes of the ejector system should be fully understood. This paper presents the computational results for the two-dimensional supersonic ejector system with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the diffuser exit. For a wide range of the operating pressure ratio the flow field inside the ejector system is investigated in detail. The results show that the supersonic ejector systems have an optimal throat area for the operating pressure ratio to be minimized.

• 한국군사과학기술학회지
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• 제7권4호
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• pp.138-145
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• 2004

Experimental study was conducted on cylindrical supersonic diffuser in order to investigate the effects of the ratios of diffuser area to nozzle throat area (Ad/At), diffuser area to nozzle exit area (Ad/Ae), nozzle exit area to its throat area (Ae/At), and diffuser length to its diameter (L/D), the free volume of vacuum chamber, and the relative distance between nozzle exit and diffuser inlet on the diffuser performance. The study showed that the minimum diffuser starting pressure (Po/Pa)st increased monotonically with increase in (Ad/At) as predicted by the normal shock and momentum theory models and the volume of vacuum chamber affected vacuum pressure level during diffuser operation at lower value of (Ad/Ae). The results of this investigation will be utilized in the design of real-scale high-altitude simulation test facility.

• 한국항공우주학회지
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• 제35권5호
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• pp.426-437
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• 2007

초음속 흡입구는 설계점에서 안정된 작동을 보이지만 탈설계점에서는 흔히 버즈라고 불리는 공력 불안정성에 직면하게 되고, 결과적으로 현저한 엔진 성능의 저하를 초래하게 된다. 버즈의 일반적인 특성을 파악하기 위해 1단 꺽임각을 갖는 외부 압축식 축대칭 흡입구를 이용하여 실험적, 수치적 연구를 수행하였다. 본 연구를 통해, 흡입구 목에서 박리에 의한 흡입구 질식이 버즈의 주요 원인임을 밝힘으로써 버즈 현상의 메커니즘을 파악하였다. 여러 면적비율에 따라 간헐적 버즈와 연속적 버즈가 관찰되었고 그 천이과정이 파악되었다. 면적비율이 감소할수록 버즈 주파수가 증가하였으나, 각 면적비율에서 흡입구 내 모든 위치의 압력 진동 주파수는 동일한 특성을 갖는다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.992-995
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• 2011

초음속 공기 흡입식 추진시스템(램제트/스크램제트)에 적용되는 공기 흡입구의 성능설계 기법 연구를 수행하여 두 종류의 공기 흡입구에 대한 예비 형상 설계 및 성능해석 모델을 수립하였다. 제시된 모델을 사용하여 축대칭 원추형 공기 흡입구와 2차원 사각형 공기 흡입구의 압축 각도와 충격파 개수에 따른 성능 영향을 평가하였다.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.260-267
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• 2016

The design process of blended inlet body (BIB) for the preliminary design of a near-space high supersonic unmanned aerial vehicle (HSUAV) is presented. The mass flow rate and cowl area of inlet at a design point are obtained according to the cruise condition of the HSUAV. A mixed-compression axisymmetric supersonic inlet section with a fixed geometry reasonably matching the high supersonic cruise state is created by using the inviscid theory of aerodynamics. The inlet section is optimized and used as a baseline section for the BIB design. Three BIB concepts for the HSUAV are proposed, and their internal aerodynamic characteristics of inlet are evaluated using Euler computational fluid dynamics (Euler CFD) solver. The preferred concept is identified, in which the straight leading edge of the baseline HSUAV configuration is modified into the convex leading edge to accommodate the inlet and meet the requirements of the cowl area to capture the sufficient air flow. The total recovery of inlet for the preferred BIB concept and the aerodynamic characteristics of the modified HSUAV configuration are verified using Navier-Stokes computational fluid dynamics (NS CFD) solver. The validation indicates that the preferred BIB concept can meet both the requirements of the inlet and aerodynamic performance of the HSUAV.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.520-524
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• 2000

A ejector system is one of the fluid machinery, which has been mainly used as an exhaust pump or a vacuum pump. The ejector system has often been pointed out to have only a limited efficiency because it is driven by pure shear action and the mixing action between primary and secondary streams. In the present work, numerical simulations were conducted to investigate the effects of the geometry and the mass flow ratio of supersonic ejector-diffuser systems on their mixing performance. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations, and the standard ${\kappa}-{\varepsilon}$ turbulence model was used to close the governing equations. The flow fields of the supersonic ejector-diffuser systems were investigated by changing the ejector throat area ratio and the mass flow ratio. The existence of the second throat strongly affected the shock wave structure inside the mixing tube as well as the spreading of the under-expanded jet discharging from the primary nozzle, and served to enhance the mixing performance.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1231-1237
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• 2004

Determination of geometric design parameters of a second-throat type annual supersonic ejector is described. Tested geometric parameters were primary nozzle area ratio, cross-sectional area of second-throat, L/D ratio of second-throat and primary flow injection angle. Varying these four geometric parameters, we build a test matrix made of 81 test conditions, and experimental apparatus was fabricated to accommodate them. For each test condition, the stagnation pressure of primary flow and the static pressure of the secondary flow were measured simultaneously along with their transition to steady operation and finally to unstarting condition. Comparing the performance curve of every case focused on starting pressure, the unstarting pressure and the minimum secondary pressure, we could derive correlations that the parameters have on the performance of the ejector and presented the optimal design method of the ejector. Additional experiments were carried out to find effects of temperature and mass flow rate of the secondary flow.

• International Journal of Aeronautical and Space Sciences
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• 제9권2호
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• pp.98-106
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• 2008

The motive gas of a supersonic ejector is supplied from different sources depending on the application. The performance of an ejector that is represented by the secondary flow pressure, starting and unstarting pressures heavily depends on the molecular properties of the motive gas. The effects of specific heat ratio of the motive gas were investigated experimentally for an axi-symmetric annular injection type supersonic ejector. Both the starting pressure and unstarting pressure, however, decreased with the increase of the specific heat ratio of the motive gas. It was discovered that the secondary flow pressure increased as the specific heat ratio of the motive gas decreased even if the stagnation pressure of the motive flow was invariant. However, when the motive gas flow nozzle area ratio is large enough for the motive gas to be condensed, different tendency was observed.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.303-306
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• 2007

고고도 모사용 초음속 디퓨져의 설계 및 작동인자에 대한 영향을 파악하기 위하여 압축성 축대칭 Wavier-Stokes 방정식 기반의 two-layer k-$\varepsilon$ 난류 수치해석과 실험 결과를 비교 분석하였다. 디퓨져의 설계 및 작동인자인 노즐과 디퓨져의 면적비, 진공챔버의 크기, 제트의 공급압력에 대한 디퓨져내 유동 발달과 디퓨져 작동 특성을 살펴보았다.