• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.55-58
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• 2006

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The three different kinds of confined slot were applied to the jet with a view to evaluating the shape effect and the jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. It was found that the vortex structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Finally, the slot shape was proved to be related with the generation timing of vortex pair and the temporal vortex structure.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.1-11
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• 2002

The suitable turbulence model is found to be required in the course of establishing a proper analysis methodology for thermal stripping phenomena which are shown in strong temperature variation area such as reactors and propulsion devices. Three different turbulence models of $\kappa$-$\varepsilon$ model, modified $\kappa$-$\varepsilon$ model, and full Reynolds stress(FRS) model, are applied to analyze unsteady turbulent flows with temperature variation. Three test cases are selected for verification. These are vertical jet flows with water and sodium, and parallel jet flow with sodium. Analysis yields the conclusion that 3-D computation with FRS betters others. However, modified modeling is required to improve its heat transfer characteristic analysis. Further analysis is performed to find momentum variation effects on temperature distribution. It is found that the momentum increase results increase of fluid mixing and magnitude of temperature variation.

• 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.1
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• pp.9-16
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• 2005

Jet vane is an useful component which is installed at the end of a nozzle for the purpose of the posture control and the secure controlling stability during the initial launching of a rocket. During several seconds from its initial launching moment, the JV driving part is heated due to the direct contact of the vane with the combusted gas and the vane is ablated mechanically or chemically. In this study, as the fundamental study for the thermal analysis of jet vane, the heat transfer into a jet vane which is located in the uniform supersonic flow field is calculated. For this, boundary layer integral method and finite difference method are used simultaneously. Based on the thermal boundary conditions derived from the analysis, the transient heat conduction in the vane is also calculated.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.1
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• pp.58-65
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• 2018

To improve the performance of high-speed vehicles, various studies have been carried out on the head of vehicles. In this study, tests are conducted on flow characteristics and drag reduction using counterflow air jets in supersonic flow. The flow is visualized by the Schlieren method using a high-speed camera, and the drag is measured using a torque sensor according to the injection pressure conditions. The results of the measurements indicate that the flow changes from unsteady state to steady state for injection pressure ratios between 1.58 and 1.70, and drag reduction is observed as the pressure of the counterflow air jets increases.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1494-1498
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• 2004

Transition sequence of rocket to ramjet was simulated numerically for a two-dimensional axisymmetric can-type ramjet engine. Multi-species preconditioned Navier-Stokes equations with $k-{\varepsilon}$ turbulence model and finite-rate chemistry model was employed. To calculate transition sequence, initial flow-field conditions for inlet diffuser with closed port-cover was computed first, and then that result was applied as initial conditions after port-cover opened. Terminal shock was developed as a result of increased pressure in a combustor due to combustion and ramjet operated at supercritical condition. For a smaller nozzle throat area, buzz instability was occurred. Strong pressure oscillations were observed as a result of forward and backward movement of terminal shock and those oscillations were not damped out.

• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.23-27
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were Investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using cinematic Particle Image Velocimetry technique.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.57-62
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• 2005

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using proper orthogonal decomposition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.5
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• pp.329-339
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• 2017

Impingement jets have been applied in a wide variety of fields as they provide significantly high heat transfer on the impingement-jet stagnation zone. However, the crossflow in an impingement chamber developed by spent wall jets can disrupt and deflect the downstream jets in the array, leading to a decrease in the cooling performance of an array of impingement jets. A numerical analysis is made of the fluid flow and heat transfer characteristics in a corrugated structure that traps the spent air in the corrugations between impingement jets and reduces crossflow effects on downstream jets. All computations are performed by considering a three-dimensional, steady, and incompressible flow by using the ANSYS-CFX 15.0 code. The effects of the configuration parameters of the corrugated structure on crossflow reduction of the array of impingement jets are presented and discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1087-1096
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• 2001

The dynamic structures of unsteady CH$_4$/Air jet diffusion flame with a flame-vortex interaction were numerically investigated. A timed-dependent, axisymmetric computational model and a low mach number approximation were employed in the present calculation. A two-step global reaction mechanism which considers 6 species, was used to calculate the reaction rates. The predicted results including the gravitational effect show that the large outer vortices and the small inner vortices can be well simulated without any additional disturbances near nozzle tip. It was found that the temperature and species concentrations have deviated values even for the same mixture fraction in the flame-vortex interaction region. It was also shown that the flame surface is not deformed by the inner vortex in upstream region, while in downstream region, the flame surface is compressed or stretched by the outer vortex roll-up. The present unsteady jet flame configuration accompanying a flame-vortex interaction is expected to give good implications for the unsteady structures of turbulent flames.