• Journal of Hydrospace Technology
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• 제1권1호
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• pp.41-56
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• 1995

Flew control devices, such as flow liners, are frequently introduced in a cavitation tunnel in order to reduce the tunnel blockage effect, when a three-dimensional wake distribution is simulated using a complete ship model or a dummy model. In order to estimate the tunnel wall effect and to evaluate the effect of flow liners on the simulated wake distribution, a surface panel method is adopted for the calculation of the flow around a ship model and flow liners installed in a rectangular test section off cavitation tunnel. Calculation results on the Sydney Express ship model show that the tunnel wall effect on the hull surface pressure distribution is negligible for less than 5% blockage and can be appreciable for more than 20% blockage. The flow liners accelerate the flow near the afterbody of the ship model, so that the pressure gradient there becomes more favorable and accordingly the boundary layer thickness would be reduced. Since the resulting wake distribution is assumed to resemble the full scale wake, flow liners can also be used to simulate an estimated full scale wake without modifying the ship model. Boundary taper calculation should be incorporated in order to correlate the calculated wake distribution with the measured one.

• 대한기계학회논문집B
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• 제24권2호
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• pp.298-305
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• 2000

The flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices were studied experimentally. The test facility consisted of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta wings protruding from the surface. In order to control the strength of the longitudinal vortices, the angles of attack of the vortex generators were varied from - 20 degree to - 45 degree, but spacings between the vortex generators were fixed to 4 cm. The 3-dimensional mean velocity measurements were made using a five-hole pressure probe. Heat transfer measurements were made using the thermochromatic liquid to provide the local distribution of the heat transfer coefficient. Unlike common flow down, common flow up vortices moved toward the centerline as they developed and interacted strongly with each other but not with the boundary layer. Spanwise profiles of Stanton number were similar for ${\beta}=-20^{\circ}\;and\;-35^{\circ}$, but not similar for ${\beta}=-45^{\circ}$. The case of ${\beta}=-20^{\circ}\;and\;-35^{\circ}$ showed the two peak Stanton number, but the case of ${\beta}=-45^{\circ}$ showed the only one peak Stanton number.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2002년도 제18회 학술발표대회 논문초록집
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• pp.41-42
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• 2002

The powered missiles with very high thrust level can make highly underexpanded jet plume downstream of tile exhaust nozzle exit so that strong interactions between the exhaust plume and a free stream occur around the body at transonic or supersonic speeds. The interactions result in extremely complicated flow phenomena, which consist of plume-induced boundary layer separation, strong shear layers, various shock waves, and interactions among these. The flow characteristics are inherent nonlinear and severe unstable during the flight at its normal speed as well as taking-off and landing. Eventually, the induced boundary layer separation and pitching and yawing moments by the interactions cause undesirable effects ell the static stability and control of a missile.

• 대한기계학회논문집B
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• 제28권1호
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• pp.89-98
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• 2004

In this paper, we develope a dispersion model based on the Generalized Langevin Model. Thomson's well-mixed condition is the well known criterion to determine particle dispersion. But, it has 'non-uniqueness problem'. To resolve this, we adopt a turbulent model which is a new approach in this field of study. Our model was greatly simplified under the self-similarity condition, leaving model only two model constants $C_{0}$ and ${\gamma}$$_{5}$ that control the dispersion and spin which measures rotational property of the Lagrangian particle trajectory. We investigated the sign of spin as well as magnitude by using the Direct Numerical Simulation. Model calculations were performed on the neutrally stable boundary layer flow. We found that spin has weak effect on the particle dispersion but it shows the significant effect on the horizontal flux compared to the zero-spin model.

• International Journal of Aeronautical and Space Sciences
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• 제2권1호
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• pp.12-19
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• 2001

Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.

• 대한조선학회논문집
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• 제40권5호
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• pp.10-16
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• 2003

To investigate the jet effect on circulation control, a segment of model was prepared and inserted horizontally across the test section of the cavitation tunnel. The hydrodynamic forces acting on the model were measured under the 2 dimensional flow behavior. Circulation flow control requires higher flow rate of water jet than boundary layer control does. Jet injection is effective in increasing lift coefficient and the increments reach to 160% in a certain combination of parameters such as an angle of attack, jet flow rate and flap angle. The blown water jet not only reduces form drag but also thrust effect, which is sometimes greater than the form drag in specific conditions.

• 해양환경안전학회지
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• 제24권1호
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• pp.92-100
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• 2018

난류경계층이 유지되기 위한 에너지 공급은 경계층 내 구조물인 와류들의 상호작용으로 끊임없이 이루어진다. 이러한 난류 유동은 수송분야의 마찰저항 및 해양구조물의 침식 및 진동을 유발하기 때문에 유동 제어를 위한 연구가 활발히 진행되고 있다. 이러한 제어의 극대화를 위해서는 난류 에너지 전달이 어떻게 이루어지는지에 대한 메카니즘 규명이 필수적이고, 이를 위해서는 층류경계층 내 유동현상으로 파악하는 것이 명확하고 용이하다는 장점이 있다. 따라서, 본 연구에서는 층류경계층 내 평판에 반구를 설치하여 역압력구배을 발생시킴으로써 교란된 유동현상의 상호작용을 분석하였다. 즉, 반구를 둘러싼 목걸이 와류와 반구 표면의 유동 박리에 의한 후류영역에서 머리핀 와류가 생성되어 상호 유기적으로 영향을 주고받는다. 이 과정에서 목걸이 와류는 후류영역으로 높은 운동량의 유체를 유입시켜 머리핀 와류의 발생 주파수를 증가시킨다. 반구 전방에 구멍을 뚫어 국부적인 흡입제어로 목걸이 와류의 와도를 감소시킴으로써 그 영향이 완화되는 과정을 유동 가시화 및 열선유속계로 측정하여 정성 및 정량적으로 분석하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.327-330
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• 2006

공동부 위에 설치된 슬롯판을 이용한 경사충격파와 난류 경계층의 간섭유동의 피동제어에 관한 수치적 연구가 수행되었다. 얻어진 수치결과는 피토압력/벽압력 분포와 쉴리렌 유동가시화 등 동일한 경계조건에서 수행된 실험결과와 비교되었으며, 두 결과가 서로 잘 일치하고 있음이 확인되었다. 또한 슬롯의 위치와 개수, 슬롯의 각도 등 슬롯판의 다양한 형상변화가 간섭유동에 미치는 영향이 추가로 관찰되었다. 이러한 슬롯의 형상변화가 간섭유동에 미치는 영향을 정량적으로 파악하기 위하여, 간섭유동 후방의 피토압력 및 전압 변화, 경계층 특성변화, 그리고 슬롯판을 통하여 공동부 내부로 유출입하는 질량유량의 변화 등이 관찰되었다.

• 대한전자공학회논문지SD
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• 제44권1호
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• pp.22-27
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• 2007

반도체 또는 평판디스플레이 제조에 있어 노광공정 후의 PR(photoresist) 제거 공정으로 이용하기 위하여 경계 막 제어에 의한 오존처리공정 및 설비 구현에 대한 연구를 수행하였다. 개발한 초 고농도 오존생성기술과 vapor 발생 방식 경계 막 제어 오존처리공정설비에 의해 실리콘 웨이퍼 PR 제거시험을 수행하였으며 오존가스농도 16wt%, 오존가스 유량 $8[\ell/min]$에서 약 400nm/분의 높은 PR 제거율을 달성하였다.

• 한국전산유체공학회지
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• 제18권4호
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• pp.82-89
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• 2013

Database of a bleed model has been corrected and numerical simulations have been performed to control buzz using the corrected bleed model. The existing bleed model, which was developed as a part of a boundary condition model for porous bleed walls, underestimates bleed flow rate because flow accelerations near the bleed regions are ignored. Also, it overpredicts the sonic flow coefficient when the bleed plenum pressure ratio is high. To correct these problems, and to enhance the performance of the bleed model, the database has been corrected using CFD simulations to compensate for the flow acceleration near the bleed region. Futhermore, the database of the bleed model is extended with the second order extrapolation. The corrected bleed model is validated with numerical simulations of a shock-boundary layer interaction problem over a solid wall with a bleed region. Using the corrected bleed model, numerical simulations of supersonic inlet buzz are performed to find the deterrent effects of bleed on buzz. The results reveal that bleed is effective to prevent buzz and to enhance the inlet performance.