• 한국군사과학기술학회지
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• 제5권3호
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• pp.77-86
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• 2002

An experimental study of the vortex interaction characteristics of a delta wing/LEX configuration was conducted in a wind tunnel using the micro water droplet and laser beam sheet visualization technique. The main focus of this study was to analyze the effect of the angle of attack and sideslip angle on the vortex interaction and vortex breakdown. These tests were accomplished at angles of attack between $16^{\circ}$ and $28^{\circ}$ and sideslip angle between $0^{\circ}$ and $-15^{\circ}$ at free-stream velocity of 6.2 m/s. Flow visualization data provide a description of the vortex interaction between LEX and wing vortices, and of the vortex breakdown. The introduction of LEX vortex stabilized the vortical flow, and delayed the vortex breakdown up to higher angle of attack. The vortex interaction and breakdown was promoted on the windward side, whereas they are suppressed on the leeward side.

• 한국전산유체공학회지
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• 제13권2호
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• pp.8-13
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• 2008

A supersonic viscous flow over a five-degree half-angle cone is studied computationally with three-dimensional Navier-Stokes equations. Steady asymmetric solutions show that the asymmetric flow separation is caused by convective instability. The effects of angle of attacks, Reynolds numbers, and Mach numbers have been investigated and it is found that those factors affect the generation of the side force. The side force has the maximum value at ${\alpha}=22^{\circ}$, while over ${\alpha}=22^{\circ}$, asymmetric vortex becomes transient, which results in the unsteady shedding. At the angle of attack of 22 degrees, the side force increases with Reynolds number and decreases with Mach number. The increase of the side force stops over the critical Reynolds number for the present configuration.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2109-2114
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• 2003

The vortex flow characteristics of a yawed LEX-delta wing at a high-angle of attack are studied using a computational analysis. The objective of the present study is to investigate and visualize the effects of the yaw angle, the development and interaction of vortices, the relationship between the suction pressure distributions and the vortex flow characteristics. Computations are applied to the three dimensional, compressible, Navier-Stokes Equations. In computations, the yaw angle is varied between 0 and 20 degree at a high-angle of attack. Computational predictions are compared with the previous experimental results.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.171-176
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• 2007

Supersonic viscous flow over a 5 degree half angle cone studied computationally with three-dimensional Navier-Stokes equations. Steady asymmetric solutions of 5-deg half angle cone show that the asymmetric flow separation is caused by convective instability. The angle of attack, Reynolds number, and Mach number affected the side force variation that is caused by asymmetric vortical flow.

• Journal of Mechanical Science and Technology
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• 제20권1호
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• pp.167-175
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• 2006

A parametric study has been accomplished to figure out the effects of elliptic cylinder thickness, angle of attack, and Reynolds number on the unsteady lift and drag forces exerted on the elliptic cylinder. A two-dimensional incompressible Navier-Stokes flow solver is developed based on the SIMPLER method in the body-intrinsic coordinates system to analyze the unsteady viscous flow over elliptic cylinder. Thickness-to-chord ratios of 0.2, 0.4, and 0.6 elliptic cylinders are simulated at different Reynolds numbers of 400 and 600, and angles of attack of $10^{\circ},\;20^{\circ},\;and\;30^{\circ}$. Through this study, it is observed that the elliptic cylinder thickness, angle of attack, and Reynolds number are very important parameters to decide the lift and drag forces. All these parameters also affect significantly the frequencies of the unsteady force oscillations.

• Wind and Structures
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• 제34권5호
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• pp.437-450
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• 2022

Vortex-induced vibration (VIV) is a significant concern when designing slender structures with square cross sections. VIV strongly depends on structural dynamics and flow states, which depend on the conditions of the approaching flow and shape of a structure. Therefore, the effects of the angle of attack on the coupling effects of VIV for a square cylinder are expected to be significant in practice. In this study, the aerodynamic forces for a fixed and elastically mounted square cylinder were measured using wind pressure tests. Aerodynamic forces on the stationary cylinder are firstly discussed by comparisons of variation of statistical aerodynamic force and wind pressure coefficient with wind angle of attack. The coupling effect between the aerodynamic forces and the motion of the oscillating square cylinder by VIV is subsequently investigated in detail at typical wind angels of attack with occurrence of three typical flow regimes, i.e., leading-edge separation, separation bubble (reattachment), and attached flow. The coupling effect are illustrated by discussing the onset of VIV, characteristics of aerodynamic forces during VIV, and interaction between motion and aerodynamic forces. The results demonstrate that flow states can be classified based on final separation points or the occurrence of reattachment. These states significantly influence coupling effects of the oscillating cylinder. Vibration enhances vortex shedding, which creates strong fluctuations in aerodynamic forces. However, differences in the lock-in range, aerodynamic force, and interaction process for angles of attack smaller and larger than the critical angle of attack revealed noteworthy characteristics in the VIV of a square cylinder.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.533-539
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• 1993

In this paper, two side-attack guidance laws for an underwater vehicle are considered. In order to find the guidance command, we first make use of the optimal guidance law with terminal impact angle constraint. Secondly, the optimal solution of tracking problem is used. This paper shows some brief theory which is used in deriving the side-attack guidance laws, and the method of computing these guidance laws. Simulations on underwater vehicle for a constant moving target prove that the suggested side-attack guidance laws have enhanced side attack performance over the optimal guidance law with miss distance weighting only. Furthermore, from simulation results. we conclude that the guidance law using the optimal solution of tracking problem is more efficient for the side-attack guidance than the optimal guidance law with terminal impact angle constraint.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.434-440
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• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• 한국항공우주학회지
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• 제43권3호
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• pp.224-231
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• 2015

람다 날개 형상의 공력 계수에 대한 실험적 연구를 국방과학연구소의 중형아음속 풍동에서 수행하였다. 본 연구의 주목적은 옆미끄럼각의 변화에 따라 다양한 공력 계수가 어떻게 변화하는지를 조사하는 것이다. 옆미끄럼각이 $0^{\circ}C$인 경우, 피칭 모멘트가 급격히 불안정해지는 현상을 확인하였으며, 옆미끄럼각이 증가함에 따라 pitch break 현상이 더 높은 받음각에서 발생하는 것을 확인하였다. 롤링 모멘트는 옆미끄럼각이 있는 경우 pitch break와 유사한 특성을 보여준다. 이런 경향은 옆미끄럼각이 증가할수록 더 심하게 나타났다. 요잉 모멘트는 높은 받음각에서 옆미끄럼각에 따라 기울기가 크게 변화하였고 불안정한 방향 안정성이 뚜렷이 나타났다. 모멘트의 이런 특성들은 비행 제어를 위해서는 보다 효과적인 조종성 증가 장치가 필수적이란 것을 의미하고 있다.

• 수산해양기술연구
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• 제38권3호
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• pp.234-240
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• 2002

본 연구에서는 전개판의 영각 변화에 따른 정적안정성에 관하여 이론적 해석을 하였다. 또한 전개판의 형상별 유체력에 의한 정적 안정성을 평가하기 위하여 종횡비가 다른 평판과 만곡도가 다른 종만곡판을 사용하여 회류수조에서 유체력 및 모벤트를 측정하고 형상별 압력중섬계수와 모멘트 계수를 계산하였다. 본 연구에서 얻어진 결과를 요약하면 다음과 같다. 1. 전개판의 영각($\alpha$) 변화에 따른 끌줄의 장력과 후릿줄의 장력에 의한 모멘트 변화는 전개판을 항상 정적 안정성을 가지도록 작용한다. 2. 종횡비(λ)가 0.5, 1.0, 1.5인 평판의 압력중심계 수는 영각의 증가와 함께 전연에서 중심쪽으로 이동한다. 이것은 유체력에 의한 모멘트는 항상 정적으로 안정하도록 작용한다는 것을 의미한다. 3. 종횡비가 일정(λ=1.5)하고, 만곡도(CR)가 5%, 10%, 15%, 20%인 만곡판의 유체력에 의한 압력중심계수는 영각의 증가와 함께 후연에서 전연쪽으로 이동한 다음, 다시 만곡판의 중심쪽으로 이동한다 만곡판에 작용하는 유체력에 의한 모멘트는 만곡도가 커질수록 정적으로 불안정한 영각의 범위가 증가한다.