• 한국항공우주학회지
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• 제34권3호
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• pp.1-5
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• 2006

자연에 존재하는 새나 곤충들은 양력 및 추력을 발생하기 위하여 평균캠버선의 형상을 변화시킨다. 기존의 비정상 박익 이론들은 주로 강체 플랩핑 에어포일에 관하여 유도되어 왔다. 생체형상가변익의 비정상 공력특성을 파악하기 위하여 변형 가능한 에어포일에 대한 확장된 비정상 박익이론이 필요하다. 생체형상가변익의 비정상 공력특성을 계산하기 위해 Theodorsen의 접근방법을 확장하였다. 에어포일의 평균 캠버선은 다항식으로 나타내었다. 형상 가변익에 작용하는 비정상 공력특성을 순환항 및 비순환항으로 나누어 나타내었다. 본 이론은 플래핑운동을 하는 생체형상가변 에어포일의 비정상 공력해석 및 모핑날개의 공탄성 해석에 적용가능하다.

• 한국가시화정보학회지
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• 제21권2호
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• pp.83-90
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• 2023

The shape of an airfoil is a critical factor in determining aerodynamic characteristics such as lift and drag. Aerodynamic properties of an airfoil have a decisive impact on the performance of various engineering applications, including airplane wings and wind turbine blades. Therefore, it is essential to analyze the aerodynamic characteristics of airfoils. Various analytical tools such as experiments, computational fluid dynamics, and Xfoil are used to perform these analyses, but each tool has its limitation. In this study, airfoil parameterization, image recognition, and artificial intelligence are combined to overcome these limitations. Image and coordinate data are collected from the UIUC airfoil database. Airfoil parameterization is performed by recognizing images from image data to build a database for deep learning. Trained model can predict the aerodynamic characteristics not only of airfoil images but also of sketches. The mean absolute error of untrained data is 0.0091.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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• pp.174-180
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• 1999

Aerodynamic characteristics of tandem airfoil under ground effect is investigated numerically. Some numerical results for NACA 6409 tandem airfoil are presented. The numerical results show that as being decreased distance between airfoils, the lift coefficient of leading airfoil is increased and that of trailing airfoil is decreased. Drag coefficient shows opposite property, At the same distance between leading airfoil and trailing airfoil, lower position of trailing airfoil give better tandem airfoil effect.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.478-481
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• 2009

As a first step for aerodynamic analysis of vertical axis wind turbine, dynamic stall characteristics of airfoil was investigated. Dynamic stall of wind turbine airfoil is caused by severe variation of angle of attack and relative velocity of flow around airfoil. Angle of attack and relative velocity can be expressed with tip speed ratio. Variation of angle of attack is strongly dependent on the tip speed ratio. For tip speed ratio, 1.4 and free stream velocity, 15m/s, dynamic stall characteristics of wind turbine airfoil is compared with those of oscillating airfoil having same angle of attack variation.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.203-208
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• 2016

In this paper, vibration characteristics in terms of the airfoil cross-sectional shape was examined by using the EDISON co-rotational plane beam-transient analysis. Assuming aircraft wing as a cantilevered beam with a constant cross-sectional shape, natural frequencies of each airfoil shape was compared while varying airfoil maximum thickness and maximum camber length, using Fast Fourier Transformation(FFT). When the airfoil maximum thickness was varied, natural frequency showed peak value at 18% chord, and decreased afterwards. When the airfoil maximum camber length was varied, natural frequency either increased or decreased at 6% chord, while at 8% the natural frequency showed its maximum. Applying such trends to B-737 wing airfoil, an improved B-737_mod airfoil shape was obtained with regard to the vibration characteristics.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.206-209
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• 2011

During landing approach, an airplane could experience dynamic unstable motion by the combination of a gust and elevator control to cancel the disturbances. This situation is dangerous and could lead to a loss of an airplane. In this paper, numerical analysis was used to study the effect of pitch oscillating 2-D high lift devices in a landing condition. Experimental data on a pitching naca0012 airfoil was used for code validation. Dynamic characteristics of an airfoil, single slotted flap for mid-class passenger aircraft were analyzed. Unsteady Navier-Stokes analysis was performed with Spalart-Allmaras turbulence model for separation dominant low speed flow. As a result, flow hysteresis of a flapped airfoil was more complex than that of an oscillating airfoil. So, dynamic analysis of a flap in a landing condition is very important for operational safety.

• 한국항공운항학회지
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• 제21권1호
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• pp.45-50
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• 2013

In this study, lumped-vortex element method and thin airfoil theory were used to analyze aerodynamic characteristics of airfoils with relative motion that had camber lines of NACA $44{\times}{\times}$ airfoil in 2-dimensional unsteady incompressible potential flow. Velocity disturbance due to airfoil was calculated by lumped-vortex element model and force distribution on airfoil by unsteady Bernoulli's equation. Variables in relative motion were considered the period p, the amplitude of flapping $A_f$ and pitching $A_p$, and the phase difference between flapping and pitching ${\phi}_p$ and the angle of attack ${\alpha}$. Due to movement of an airfoil, dag was induced in 2-dimensional unsteady incompressible potential flow. The numerical results show that the aerodynamic characteristics of the airfoil with flapping and pitching at the same time are illustrated. Especially the mean lift coefficient became smaller, but drag coefficient became larger.

• 한국항공우주학회지
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• 제34권3호
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• pp.6-13
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• 2006

본 연구에서는 저 레이놀즈수 유동에서 flapping운동을 하는 익형이 가질 수 있는 2차원 평면상의 운동궤적에 따른 공력특성을 연구하였다. 익형이 유동흐름방향으로 왕복 운동하는 lead-lag운동과 plunging운동의 조합으로 2차원 평면상에 나타날 수 있는 여러 운동궤적을 합성하여 flapping 주파수 변화에 따른 공력계수들의 변화를 살펴보았다. 상하방향의 순수 plunging운동에 lead-lag운동을 추가함으로써, 평균추력계수와 평균양력계수를 증가시킬 수 있는 운동궤적이 존재함을 확인하였다. 아울러 운동주기 동안 나타나는 추력계수와 양력계수의 변화를 비교하여 upstroke와 downstroke시 나타나는 공력특성을 파악하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.199-201
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• 2011

NACA0012 Airfoil was simulated with Computational Fluid Dynamics(CFD) and the aerodynamic characteristics was analyzed for various far-field boundary distances ranging from 10 airfoil chord to 50 chord Drag coefficient distribution was dependent on the far-field distance and circulation, integrated along the loop inside the flow region, was also dependent. It was turned out that some corrections based on the circulation should be added to the far-field boundary condition for accurate airfoil simulation.

• International Journal of Aerospace System Engineering
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• 제2권1호
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• pp.53-57
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• 2015

For improving the efficiency of near space propellers working over 20km, performances of their streamwise sections, i.e. low-Reynolds-number airfoils which work at $10^4-10^5$ Reynolds numbers, are significant. Based on the low-Reynolds-number CFD technology, this paper designs a novel low-Reynolds-number airfoil. Unsteady characteristics of the laminar separation bubble on novel airfoil and a typical conventional airfoil are studied numerically, and the Reynolds number effect is investigated. Results show that at $10^4-10^5$ Reynolds numbers, unsteady aerodynamic characteristics of the novel airfoil are severely weakened and its lift-to-drag ratio can increase about 100%.