• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.50-56
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• 2008

본 논문에서는 실린더 주위유동의 B-mode에 해당하는 레이놀즈 수 $300{\sim}1000$범위에서 고차 고해상도 기법(OHOC Scheme)을 이용하여 원형 실린더 주위의 유동장 및 음향장 특성에 대해서 연구하였다. B-mode 레이놀즈 수 범위에서 스팬방향 길이에 따른 3차원 원형실린더의 스트롤 수, 양 항력계수의 상관관계에 대해 수치계산 및 실험 결과와 비교 분석한 결과 매우 잘 일치하는 것을 보였다. 그리고 이 결과를 토대로 하여 B-mode 불안정성 영역에서 보다 정확한 2차 와류 모사를 위한 적절한 스팬방향을 찾고, 3차원 후류유동의 불안정성이 음향장의 변화에 미치는 영향을 정성적으로 고찰하여, 3차원 원형실린더의 공력소음 대한 기초적인 연구를 수행하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.497-508
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• 1985

본 논문에서는 일양한 예혼합 기류중에 놓여진 원주 후류의 고온 순환류에 의 해 보지되는 난류 예혼합 화염을 대상으로 해서 유동의 가시화 및 온도와 이온전류의 변동의 측정에 의해서 화염의 구조를 조사한 결과, 원주 보염기 후류의 재순환 영역부 근에 형성된 전단층에 있어서는 코히렌트(Coherent)구조의 화염이 되고 하류부에서는 불규칙한 3차원 와(渦)에 지배되는 전파성 화염이 형성 되었다. 온도변동에 대한 쌍 봉성의 확율밀도분포와 이온전류변동에 대한 3개의 피이크의 확율밀도분포는 엷은 반 응면을 사이에 두고 미연혼합기괴와 기연가스괴가 서로 접하는 주름 상층류화염 또는 층류화염편의 구조에 대응하며, 코히렌트 와(渦)에 지배되는 화염에 있어서는 거시적 혼합은 코히렌트 와의 거동에 지배되나 그 구조는 주름상층류 화염과 일부 강한 전단 력을 받는 부분에는 분산 반응영역의 구조임이 밝혀졌다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.859-867
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• 2007

The objective of this study is to develop and validate a numerical method which can handle the multi-rotor aerodynamic characteristics. For the purpose of power estimation, table look-up method is implemented to the existing unsteady panel code that is coupled with a time-marching free wake model. Also, the Reynolds number scaling is implemented for the application to various regions of Reynolds number. The computed results are validated against the available experimental data for coaxial and tandem rotors. In the validation case for the coaxial rotor, more accurate result is acquired when the thickness effect is considered. The wake instability problem occurs at a particular separation distance between the rotors for tandem rotors. The wake instability is avoided by setting the single-rotor wake geometry as the initial wake geometry for the multi-rotor analysis. The estimated result for rotor separation effect is compared with the result of the momentum theory.

• Journal of Advanced Navigation Technology
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• v.14 no.4
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• pp.479-488
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• 2010

The aim of this paper is to research the change in the turbulent flow and the AOA occurred by the wind perpendicular to the direction of runway according to the three-dimensional numerical analysis. The maximum amplitude of AOA variation on runway reached $6^{\circ}$ within 1 second because of the wake formed by the constructions in the vicinity of the airport. The overall effects appeared in aperiodic forms. It was also observed the rapid flow generated between the buildings shifted into the existing wake and eventually merged with it. It is expected thai the strong wake will cause instability during takeoff and landing.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.6
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• pp.50-57
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• 2007

Pressure Sensitive Paint(PSP) means a reacting paint in pressure. PSP can measure continuous pressure field by analyzing the oxygen quantity using optical method. The surface pressure of down stream after the sonic jet that injected transversely into the supersonic freestream was measured by PSP technique. Moreover the effect of various rectangular shaped cavities in front of the jet was measured by PSP technique. A comparison of the PSP results with conventional pressure tap and CFD indicates good agreement. Until now, the results of numerical analysis were compared with the discrete points such as the results of pressure tap. In this study, the whole region pressure was measured using PSP technique and its results were similar to CFD. Therefore, the flow phenonenon of cavity downstream was clearly grasped.

• Journal of Korea Water Resources Association
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• v.48 no.11
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• pp.891-903
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• 2015

This paper presents numerical simulations of flow around a circular patch of vegetation using a depth-averaged two-dimensional numerical model which is capable of simulating flow structure in vegetated open channel. In order to account for vegetation effect, drag force terms are included in governing equations. Numerical simulations are conducted with various solid volume fractions (SVF). Flow passes through a circular patch and low velocity region, which is called wake region, is formed downstream of the patch. When SVF is larger than 0.08, a recirculation is observed. The location of the recirculation is moved further downstream as SVF decreases. Von-$K{\acute{a}}rm{\acute{a}}n$ vortex street is developed beyond the wake region due to interaction between two shear layers induced by a circular patch of vegetation. The vortex is developed as SVF is larger than 0.08, and the location of the vortex is consistent with the maximum of turbulence kinetic energy. The location of the peak of turbulence kinetic energy is moved further downstream as SVF decreases.

• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.36-42
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• 2004

The effect of tip clearance height on the three-dimensional flow and aerodynamic loss in the wake region of a high-turning turbine rotor cascade has been investigated with a miniature cone-type five-hole probe. Distributions of velocity magnitude, secondary velocity vectors, and total-pressure loss coefficient are presented for three tip gap-to-span ratios of h/s = 0.0, 0.5 and 1.0 percent. The result shows that with the increment of h/s, tip leakage vortex tends to be intensified and aerodynamic loss due to the leakage vortex is increased as well. In the case of h/s = 1.0 percent, aerodynamic loss in the tip-leakage flow region is found dominant in comparison with that in the passage vortex region. With increasing h/s, mass-averaged secondary loss coefficient has a greater portion in the mass-averaged total-pressure loss coefficient.

• Proceedings of KOSOMES biannual meeting
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• 2006.11a
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• pp.65-69
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• 2006

The flow around a foil with water jet was investigated using the two-frame PIV(CACTUS 3.1) system. After separation, unsteady recirculation & reattachment region was shown a result at reading edge. Separation area was decreased to 1/3 more by waterjet system with coanda effect. Angle of attack and water jet velocity was a variable in the experiment. Each parameters was controlled to $0^{\circ}\sim35^{\circ}$ and $0[m/s]\sim9.2[m/s]$. The separation of flow appearanced at first when the angle of attack is $17^{\circ}\sim18^{\circ}$, However, according to grew up of velocity, beginning of the separation was delayed. In this experiment, vortex and separation region was disappeared by blown when each parameters are low level, and separation controlled more certainly.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.45-49
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• 2006

The flow around a foil with waterjet was investigated using the two-frame PIV(CACTUS 3.1) system. After separation, unsteady recirculation & reattachment region was shown as a result at reading edge. Separation area was decreased to 1/3 more by waterjet system with coanda effect. Angle of attack and waterjet velocity was a variable in the experiment. Each parameters was controlled to $0^{\circ}{\sim}35^{\circ}$ and 0[m/s]${\sim}$9.2[m/s]. The separation of flow appearanced at first when the angle of attack is $17^{\circ}{\sim}18^{\circ}$. However, according to grew up of velocity, beginning of the separation was delayed. In this experiment, vortex and separation region was disappeared by blown when each parameters are low level, and separation controlled more certainly.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.211-219
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• 2008

A three-dimensional inviscid flow solver has been developed based on unstructured meshes for the investigation of the effect of the external stores on the tail surfaces of a generic fighter aircraft. The numerical method is based on a vertex-centered finite-volume discretization and an implicit point Gauss-Seidel time integration. The calculations were made for a steady flow and the computed results were compared with experimental data to validate the flow solver. An unsteady time-accurate computation of the generic fighter aircraft with external stores at transonic flight conditions showed that the external stores cause unsteady loading on the horizontal tail surface due to the mutual interference between their wake and the horizontal tail surface. It was shown that downward deflection of the trailing edge flap significantly reduces the undesirable interference effect.