• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.476-476
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• 2009

Periodic vortex separations generate periodic vertical forces acting on a trailing edge of an airfoil. When a natural frequency of the trailing edge of the airfoil is close to a vortex shedding frequency, an amplitude of the edge oscillation becomes maximal; it makes intensive noise called singing. Motion of the trailing edge may also feedback to the vortex shedding so that self-sustained oscillation appear, and a resonant frequency is locked in some interval of the speed of the incident flow. In this study, a theoretical model is proposed and applied for modeling an airfoil singing. Results are compared with experimental measurements which are carried out in an anechoic wind tunnel.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.2
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• pp.115-121
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• 2010

Periodic vortex separations generate periodic vertical forces acting on a trailing edge of an airfoil. When a natural frequency of the trailing edge of the airfoil is close to a vortex shedding frequency, an amplitude of the edge oscillation becomes maximal; it makes intensive noise called singing. Motion of the trailing edge may also feedback to the vortex shedding so that self-sustained oscillation appears, and a resonant frequency is locked in some interval of the speed of the incident flow. In this study, a theoretical model is proposed and applied for modeling an airfoil singing. Results are compared with experimental measurements which are carried out in an anechoic wind tunnel.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.85-94
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• 1999

Transient aerodynamic response of an airfoil to a moving plane-flap is numerically investigated using two-dimensional Euler equations with conservative Chimera grid method. A body moving relative to a stationary grid is treated by an overset grid bounded by a 'dynamic domain-dividing line' the concept of which is developed in this study. A conservative Chimera grid method with a dynamic domain-dividing line technique is applied and validated by solving the flowfield around circular cylinder moving supersonic speed. The unsteady and transient characteristics of the flow solver is also examined by computations of a oscillating airfoil and a ramp pitching airfoil respectively. The transient aerodynamic behavior of an airfoil with a moving plane-flap is analyzed for various flow conditions such as deflecting rate of flap and free stream Mach number.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.331-336
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• 2011

The flow fields over multi-element airfoils with lift-enhancing flat-plate tabs were numerically investigated. Common choice of the height of the lift-enhancing tabs usually ranges from 0.25% to 1.25% of the reference airfoil chord, and in this study the effect of the position of the tab with l%-chord height was studied by varying the distance of the tab from the trailing edge ranging from 0.5% to 2% of the reference chord. In this paper, the effects of lift-enhancing tabs with various position were studied at a constant Reynolds number on a two-element airfoil with a slotted flap. Computed streamlines show that the additional turning caused by the tab reduces the amount of separated flow on the flap.

• Journal of computational fluids engineering
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• v.10 no.2
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• pp.60-68
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• 2005

For study on the unsteady wall interference effect, flows around a forced oscillating airfoil in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The Spalart-Allmaras one-equation model is employed for the turbulence effect. The computed results of the oscillating airfoil having a thin wake showed that the lift curve slope is increased and the magnitude of hysteresis loop is reduced by the interference effects. Since the vortex around the airfoil is generated and convected downstream faster than the free-air condition, the phase of lift, drag and pitching moment coefficients was shifted. The pressure on the test section wall shows harmonic terms having the oscillating frequency contained in the wail effect.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.50-52
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• 2007

In the present paper, some difficulties encountered in predicting airfoil characteristics are described and solutions for those problems are discussed Since drag is determined by the amounts of pressure and, especially, shear stress, accurate estimation of shear stress is very crucial. However shear stress computation is dependent on the grid density and turbulence model, it should be consistent in preparing grid and turbulence model. When the transition from laminar to turbulent happen at the middle of airfoil, CFD solver should divide the region into laminar and turbulent region based on the transition location.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.9-12
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• 2012

현재 각 나라에서 고고도 무인항공기에 대한 관심이 높아지고, 우리나라 또한 여러 가지 형상의 고고도 무인항공기를 개발하기위해 노력하고 있다. 본 연구에서는 고고도 무인항공기에 사용되는 에어포일의 공력특성을 EDISON_CFD를 이용하여 분석하였다. 현재 개발된 고고도 무인항공기 중 글로벌 호크를 선정하여 그 주 날개의 Airfoil을 해석모델로 선정하고 항공기 운항시 고도 조건을 적용하여 공력특성을 분석하였다. 받음각의 범위는 $2^{\circ}{\sim}10^{\circ}$로 설정하였고 $C_l$ 및 $C_d$ 값을 계산하여 공력 특성 곡선($C_l$, $C_d$, $C_d-C_l$)을 구성하였다.

• The KSFM Journal of Fluid Machinery
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• v.4 no.2 s.11
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• pp.29-34
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• 2001

Experimental and numerical studies are conducted to investigate the flow field over a NACA0012 airfoil with ground effects. In experiment, the ground is simulated by a moving belt system. From the comparison between the experimental and numerical results, it is concluded that the velocity gradient over the ground plane causes the increments in pressure coefficient on lower surface of the airfoil and reduces the suction peak at the leading edge.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.273-284
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• 2012

In this paper, a study on the design of high speed airfoil is described. Various airfoils are investigated and existing airfoils are geometrically interpolated to generate new airfoils. An optimization method is applied to theses new airfoils and their aerodynamic performances are optimized. Through this study, it is demonstrated that the airfoil can be designed using the geometrical interpolation and the optimization method to exhibit good aerodynamic performances.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.333-339
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• 2017

최근에는 항공기의 임무 형태나 주위 환경에 따라 변할 수 있는 passive morphing airfoil에 대한 연구가 활발히 이루어지고 있다. 하지만 복잡한 모델링, 실험 과정 및 긴 해석 시간 때문에 아직 여러 chiral 구조를 체계적으로 비교하지 못 하고 있다. 본 논문에서는 이러한 chiral meso structure 중 하나인 Anti-Tetra Chiral 구조를 Hooke's law에 기반을 두어 등가 물성치를 구해보고, 사각형 모양의 연속체 요소로 등가 모델링을 하였다. 그 후, airfoil 내부에 연속체 요소를 직접 적용하여 실제 모델링한 경우와 비교해 본 결과 경향성 파악에 충분한 오차 범위를 얻을 수 있었다. 이를 통해 여러종류의 Chiral meso structure과 기하학적 변수를 적용한 에어포일을 효율적으로 해석할 수 있음을 제시할 수 있다.