• Advances in aircraft and spacecraft science
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• 제1권4호
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• pp.399-408
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• 2014

The flowfields inside a contour and a conical nozzle exhausting into a straight cylindrical supersonic diffuser are computed by solving numerically axisymmetric turbulent compressible Navier-Stokes equations for stagnation to ambient pressure ratios in the range 20 to 34. The diffuser inlet-to-nozzle throat area ratio and exit-to-throat area ratio are 21.77, and length-to-diameter ratio of the diffuser is 5. The flow characteristics of the conical and contour nozzle are compared with the help of velocity vector and Mach contour plots. The variations of Mach number along the centre line and wall of the conical nozzle, contour nozzle and the straight supersonic diffuser indicate the location of the shock and flow characteristics. The main aim of the present analysis is to delineate the flowfields of conical and contour nozzles operating under identical conditions and exhausting into a straight cylindrical supersonic diffuser.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.349-352
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• 2010

초음속 디퓨져의 유동현상 및 천이구간에 대해서 수치적 기법에 의한 분석을 수행하였다. 수치기법으로는 초음속 디퓨져의 내부유동해석을 위하여 2차원 축대칭 Navier-Stokes equation와 $k-{\epsilon}$ 난류모델을 사용하였으며, 액체 로켓엔진의 연소실의 천이 구간의 압력변화에 따라서 디퓨져 내부의 마하수 및 진공 챔버의 온도분포를 비교 검토하였다.

• International Journal of Aeronautical and Space Sciences
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• 제14권4호
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• pp.387-397
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• 2013

An assessment of two-equation turbulence models, the low Reynolds k-${\varepsilon}$ and k-${\omega}$ SST models, with the compressibility corrections proposed by Sarkar and Wilcox, has been performed. The compressibility models are evaluated by investigating transonic or supersonic flows, including the arc-bump, transonic diffuser, supersonic jet impingement, and unsteady supersonic diffuser. A unified implicit finite volume scheme, consisting of mass, momentum, and energy conservation equations, is used, and the results are compared with experimental data. The model accuracy is found to depend strongly on the flow separation behavior. An MPI (Message Passing Interface) parallel computing scheme is implemented.

• 한국추진공학회지
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• 제17권4호
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• pp.43-48
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• 2013

초음속 디퓨져에서 천이구간에 대해서 수치적 기법에 의한 분석을 수행하였다. 수치기법으로는 초음속 디퓨져의 내부유동해석을 위하여 2차원 축대칭 Navier-Stokes equation와 $k-{\epsilon}$ 난류모델을 사용하였으며, 로켓엔진 연소실의 천이 구간의 압력변화에 따라서 디퓨져 내부의 마하수 및 진공챔버의 온도 분포를 비교 검토하였다. 초음속 디퓨져의 작동과정에서 진공챔버 내부에 연소가스가 유입되어지고 이러한 현상에 따라서 진공챔버 내부의 압력 및 온도가 상승하는 결과를 확인하였다. 이러한 유동현상에 따라서 천이과정에서 압력 및 온도 상승을 방지하는 시스템이 필요하다.

• 대한기계학회논문집
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• 제19권9호
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• pp.2283-2296
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• 1995

Experiments of normal shock wave/turbulent boundary layer interaction were conducted in a supersonic diffuser. The flow Mach number just upstream of the normal shock wave was in the range of 1.10 to 1.70 and Reynolds number based upon the turbulent boundary layer thickness was varied in the range of 2.2*10$^{[-994]}$ -4.4*10$^{[-994]}$ . The wall pressures in streamwise and spanwise directions were measured for two test cases, in which the turbulent boundary layer thickness incoming into the supersonic diffuser was changed. The results show that the interactions of normal shock wave with turbulent boundary layer in the supersonic diffuser can be divided into three patterns, i.e., transonic interaction, weak interaction and strong interaction, depending on Mach number. The weak interactions generate the post-shock expansion which its strength is strong as the Mach number increases and the strong interactions form the pseudo-shock waves. From the spanwise measurements of wall pressure, it is known that if the flow Mach number is low, the interacting flow fields essentially appear two-dimensional, but they have an apparent 3-dimensionality for the higher Mach numbers.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.442-447
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• 2008

A numerical analysis has been conducted to investigate and characterize the unsteadiness of flow structure and oscillatory vacuum pressure inside of a supersonic diffuser equipped to simulate the high-altitude rocket test on the ground. A physical model of concern includes a rocket motor, a vacuum chamber, and a diffuser, which have axisymmetric configurations, using nitrogen gas as a driving fluid. Emphasis is placed on investigating physical phenomena of very complex and oscillatory flow evolutions in the diffuser operating at very close to the starting condition, i.e. minimum starting condition, which is one of major important parameters in diffuser design points of view.

• 한국추진공학회지
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• 제9권2호
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• pp.70-77
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• 2005

축소-팽창 디퓨저가 장착된 초음속 이젝터를 제작하여, 다양한 위치에서의 측정된 압력으로 부유동의 초음속 시동조건을 찾아내었다. 우선 부유동 흡입구의 크기의 영향을 알아내기 위하여 다양한 흡입구 직경으로 실험하였으며, 부유동의 초음속 시동은 흡입구 직경과 축소-팽창 디퓨저 직경의 비, d/D가 0.306 미만인 경우에만 일어났다. 이보다 큰 d/D에서는, 아음속 시동이 먼저 시작되고, 흡입구를 막으면서 주유동의 유입이 전 유동장을 채우게 되어 수직 충격파를 축소-팽창 디퓨저의 하류로 내려보내게 된다 이러한 상황에서 다시 흡입구를 열어도 히스테리시스의 영향으로 초음속 시동이 유지된다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.200-203
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• 2011

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser (SED). This paper aims at the improvement in HAT facility by focusing attention on the vertical firing rocket test stand with shock generators. Shock generators are mounted inside the SED for improving the pressure recovery. The results clearly showed that the performance of the ejector-diffuser system was improved with the addition of shock generators. The improvement comes in the form of reduction of the starting pressure ratio and the vertical height of test stand. It is also shown that shock generators are useful in reducing the total pressure loss in the SED.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.344-352
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• 2006

Evacuation performance, starting transient, and plume blowback at diffuser breakdown of a straight cylindrical supersonic exhaust diffuser with no externally supplied secondary flow are investigated. Pressure records in the transitional periods are measured by a small-scale cold-gas simulator. Flow-fields evolving in the diffuser-type ejector are solved by preconditioned Favre-averaged Navier-Stokes equations with a low-Reynolds number $k-{\varepsilon}$ turbulence model edited for turbulence compressibility effects. The present RANS method is properly validated with measured static wall pressure distributions and evacuation level at steady operation as well as the pressure records during the transition regime.

• 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.