• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.18-27
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• 2019

The flow mixing characteristics for the heated dual jets were numerically studied by using URANS (unsteady Reynolds-averaged Navier-Stokes). The increased turbulent diffusion was obtained for the compressible flow, and the thermal diffusion of incompressible flow increased more than that of compressible flow. From the results of FFT and phase portraits, periodic and quasi-periodic states were observed as the jet spacing increased. It was observed that linear variations of merging points and combined points were different because unsteady flow determined the flow mixing characteristics for a large jet spacing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.565-574
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• 2007

The flow control effect of blending Gurney flap with jet flap for flow around an NACA 0012 airfoil was numerically investigated through parameter variation of each flow control mechanism on unstructured meshes. The aerodynamic force and moment variations due to flow control were examined, and the results were compared between the blending control and each individual flow control. The results showed that the blending control required less energy input to achieve the same level of lift increment than that of the jet flap, and at the same time alleviated drag increment caused by introducing the Gurney flap.

• Journal of Welding and Joining
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• v.12 no.2
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• pp.1-10
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• 1994

노즐에서 분사되는 제트의 거동에 대해 전반적으로 고찰해보고, 실제 후판의 레이저 절단성 실험 을 통해 노즐의 영향 및 혼합가스의 절단면 질 향상효과 등을 살펴보았다. 간략히 요약하면 다음 과 같다. 아음속제트는 노즐압력을 증가함에 따라 절단압력도 증가하지만 노즐과 재료사이의 거 리를 가능한 작게 유지하여야 하는 제약이 있다. 따라서 사용중에 손상이 가기 쉽다. 이를 해결하 고자 초음속제트의 사용이 연구되고 있지만 shock의 형성으로 인해 노즐압과 절단압은 매우 비선 형적인 관계를 갖는다. 따라서 (i)고압에서도 MSD가 형성되지 않고 주기적인 압력 재상승이 나 타나도록 하거나, (ii)Laval노즐을 이용해 shock구조가 형성되지 않고 큰 절단거리를 얻도록 하는 방법이 제시되고 있다. 초음속노즐의 후판 절단 적용 가능성을 분석해 본 결과 유동 박리 현상으 로 인해 후판보다는 박판의 향상을 위해서는 적절한 조성의 혼합가스를 사용하는 것이 아주 효과 적이었으며, 보조 가수 제트를 채용해 slag제거를 효율적으로 수행 할 수 있음을 확인하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.4
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• pp.55-65
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• 2005

Mixing performance between fuel and oxidizer is a significant parameter of combustion efficiency and stability in an air-turbo ramjet combustor. Two types of petal mixer were experimented to research the mixing performance. Mixing performance and fuel distribution images were obtained for petal mixers. Planar laser-induced fluorescence(PLIF) was used to obtain 2-D fuel distribution. The obtained images were processed in order to make use of the image information to a quantitative level. The results of analyzing the fluorescence images could be useful to find better mixing performance between mixers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.48-53
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• 2005

The purpose of this investigation is to explore the possibility of using artificial mechanical means for excitation of shear layers with application in swirling jet mixing enhancement. For this purpose, a mechanical excitation device was designed and fabricated. The major system components consist of two subsonic nozzles, one swirl generator, and the excitation device. The experiments were carried out at various helical excitation modes; i.e., m=+0, m=$\pm$1, m=$\pm$2, m=$\pm$3, and m=$\pm$4. Axial mean velocity measurements were made with plane and helical wave excitation using a hot-wire anemometer. The results are compared with the baseline (plane-wave excitation) at various helical modes. The acquired data is presented in 3-D mesh plots and 2-D contour plots. It was observed that new device was effective in excitation of the helical instability waves and resulting in mixing enhancement of the swirling jet.

• Aerospace Engineering and Technology
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• v.6 no.2
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• pp.14-20
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• 2007

In this study, characteristics of jet type flame holder for ramjet engine combustors are investigated Jet flame holder can be easily controlled by the injection angle change and jet momentum variation without any thermal protection devices. Due to the intensive turbulent mixing effect, jet flame holder shows better flame holding performance than mechanical flame holders such as cavity, step and v-shape flame holder.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2000.09a
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• pp.126-132
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• 2000

하수처리장의 수중확산관에서 방류되는 부력제트는 초기혼합, 중력확장, 이송-확산 등의 과정이 시간적, 공간적으로 규모가 상이한 범위에서 일어나며, 하수방류 해역의 주변수 흐름은 지형특성과 조석의 영향을 받아 3차원적 비정상류 특성을 나타낸다. 이러한 부력제트의 거동을 모의하기 위해서는 일반적으로 근역과 원역을 분할하여 예측하는 방법을 사용하는데, 초기혼합 과정과 중력환장 과정을 예측하기 위해서는 정상상태는 가정한 특성길이 모형이나 제트적분 모형을 사용하고, 원역으로의 이송-확산 과정을 모의하기 위해서는 농도 모형이나 임자추적 모형등을 사용한다. (중략)

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.97-104
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• 2005

A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.82-91
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• 2003

Experiments to investigate the mixing performance of unlike doublet impinging jets are conducted. Reynolds number of simulants used in this study rages from 1.0 to 1.5 Cold flow test is performed to investigate the hydrodynamic effect and spray of the impinging jets are collected locally and calculated by using Rupe's mixing efficiency equation. Momentum exchanges and relative velocity ratio between two jets are taken as the main parameter to represent the effect of enlargement of the orifice diameter. As diameter ratio increases, the corresponding momentum ratio where maximum mixing efficiency occurs and relative velocity at the maximum mixing efficiency ranges 0.6 to 0.7, respectively. Penetration depth can be taken as a prominent parameter to estimate the mixing efficiency.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.81-89
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• 2014

Tandem-ejector has been devised for engine-bay cooling. In this study, 1-D model has been developed to analyze Tandem-ejector. In the model, the primary, the secondary and the tertiary flow conditions have been analyzed with isentropic process. The mixing process has been analyzed with conservation laws based on the control volume analysis. The total pressure loss of the primary flow has been analyzed under the matching condition between the static pressure of Tandem-ejector discharge flow and atmospheric pressure. Consequently, 1-D model can predict Tandem-ejector performance accurately and provide the performance map.