• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.61-66
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• 1998

An inverse method for the subsonic and transonic airfoil design was developed using the Euler equations. Two testcases were performed. One was a design of the supercritical airfoil, aiming to be used for the Korean mid-sized (100 passengers class) transport aircraft. The other was the design of an airfoil showing a good cruising performance (L/D ratio) in the high subsonic/transonic flow regimes. These testcases demonstrated the efficiency and the robustness of the developed method.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.1-7
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• 2017

To predict the transonic buffet onset for a supercritical airfoil with shock-boundary layer interactions, a practical steady approach has been proposed. In this study, it is assumed that the airfoil flow is steady even when buffet onset occurs. Steady Navier-Stokes computations are performed on the supercritical airfoil. Using the aerodynamic parameters calculated from Navier-Stokes solver, various steady approaches for predicting buffet onset are discussed. Among the various steady approaches considered in this study, Thomas' criterion based on Navier-Stokes computation has shown to be the most appropriate indicator of identifying the buffet onset for a supercritical airfoil with shock-boundary layer interactions. Good agreements have been obtained compared with the results of unsteady transonic wind tunnel tests. The present method is shown to be reliable and useful for transonic buffet onset for a supercritical airfoil with shock-boundary layer interactions in terms of practical engineering viewpoint.

• 풍력에너지저널
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• 제4권2호
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• pp.55-60
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• 2013

The mathematical implementation for inverse airfoil design of wind turbines is presented using vortex panel method based on assumptions of the two-dimensional incompressible potential flow. The vortex panel method employs linear distribution of the vortex strength to obtain the well converged solution. Stream function is adopted to get the basic formula for the inverse airfoil design, and a symmetric seed airfoil is given for initial data of the iteration approach. The final airfoil shape has been compared with the original airfoil shape for validation of the mathematical procedure.

• 한국항공우주학회지
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• 제45권3호
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• pp.202-211
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• 2017

본 연구에서는 KFLOW에서 사용하고 있는 ${\gamma}-Re_{\theta}$ 천이 모델을 사용하여 KARI-11-180 익형의 공력특성을 수치적으로 예측하고 그 결과를 실험 결과 및 XFOIL과 MSES의 결과와 비교하였다. 완전 난류모델은 천이모델에 비해 마찰항력을 크게 예측하기 때문에 전체적으로 높은 항력을 예측하는 등 천이모델과 완전 난류모델간의 차이를 확인하였다. KFLOW의 ${\gamma}-Re_{\theta}$ 모델을 사용한 결과는 실험을 통해 확인된 천이 유동 실험 결과의 특성을 잘 예측하고 있었으며 XFoil이나 MSES의 결과와도 잘 일치하고 있음을 확인하였다. 본 연구를 통해 drag-bucket현상이 익형 표면의 천이점의 급격한 변화로 인해 발생함을 확인하였다.

• Advances in aircraft and spacecraft science
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• 제10권4호
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• pp.303-315
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• 2023

The primary goal of this research is to investigate flow separation phenomena using various turbulence models. Also investigated are the effects of free-stream turbulence intensity on the flow over a NACA 0018 airfoil. The flow field around a NACA 0018 airfoil has been numerically simulated using RANS at Reynolds numbers ranging from 100,000 to 200,000 and angles of attack (AoA) ranging from 0° to 18° with various inflow conditions. A parametric study is conducted over a range of chord Reynolds numbers for free-stream turbulence intensities from 0.1 % to 0.5 % to understand the effects of each parameter on the suction side laminar separation bubble. The results showed that increasing the free-stream turbulence intensity reduces the length of the separation bubble formed over the suction side of the airfoil, as well as the flow prediction accuracy of each model. These models were used to compare the modeling accuracy and processing time improvements. The K- SST performs well in this simulation for estimating lift coefficients, with only small deviations at larger angles of attack. However, a stall was not predicted by the transition k-kl-omega. When predicting the location of flow reattachment over the airfoil, the transition k-kl-omega model also made some over-predictions. The Cp plots showed that the model generated results more in line with the experimental findings.

• 산업기술연구
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• 제22권A호
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• pp.59-65
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• 2002

The objective of this study is to provide the quantitative and qualitative computational data about the aerodynamic performance of Gurney flap on NACA 00XX airfoils and to show the optimum Gurney flap height for each airfoil. The test was performed on 7 different airfoils from NACA 0006 to NACA0024, which have a 3% chord(=c) thickness interval. For every NACA 00XX airfoil, Gurney flap heights were changed by 0.5% or 0.25% chord interval from 0 to 2.0%c to study their effects. The aerodynamic characteristics of clean and Gurney flap airfoil were compared, and the influences of Gurney flap on each airfoil were compared. As a CFD (Computational Fluid Dynamics) solver, FLUENT, based on Navier-Stokes code, was used to calculate the flow field around the airfoil. The fully-turbulent results were obtained using the standard $k-{\varepsilon}$ two-equation turbulence model. The test results showed that Gurney flap increased the lift coefficient much more than the drag coefficient over a certain range of the lift coefficient, so the lift-to-drag ratio, which is the important index of airfoil performance, was increased. Based on the test results, the relationship between the airfoil thickness and the optimum Gurney flap heights was suggested.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.568-572
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• 2000

A numerical investigation was performed to determine the effect of airfoil thickness on the optimum Gurney flap height using NACA 00XX series airfoils. Seven airfoils which have 3% chord thickness difference were used. These were NACA 0006, 0009, 0012, 0015, 0018, 0021, and 0024. A Navier-Stokes code, FLUENT, was used to calculate the flow field about airfoil. The fully turbulent results were obtained using the standard $k-{\varepsilon}$ two-equation turbulence model. To provide a check case fur our computational method, numerical studies for NACA 4412 airfoil were made and compared with already existing experimental data for this airfoil by Wadcock. For every NACA 00XX airfoil, Gurney flap heights ranging from 0.5% to 2.0% chord were changed by 0.5% chord interval and their effects were studied. With the numerical solutions, the relationship between $(L/D)_{max}$ and airfoil thickness as a function of flap height and the relationship between $(L/D)_{max}$ and flap height as a function of airfoil thickness were investigated. The same relationship for $(C_l)_{max}$ also were shown. From these results, the optimum flap size for each airfoil thickness can be determined and vice versa.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.140-146
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• 2002

The fluid induced vibration (FIV) phenomena of a 2-D.O.F airfoil system have been investigated in low Reynolds number incompressible flow region. Unsteady flows with viscosity are computed using two-dimensional incompressible Navier-stokes code. To validate developed Navier-Stokes code, steady and unsteady flow fields around airfoil are analyzed. The present fluid/structure interaction analysis is based on the most accurate computational approach with computational fluid dynamics (CSD) and computational structural dynamics (CSD) techniques. The highly nonlinear fluid/structure interaction phenomena due to severe flow separations have been analyzed fur the low Reynolds region (R$_{N}$ =500~5000) that has a dominancy of flow viscosity. The effect of R$_{N}$ on the fluid/structure coupled vibration instability of 2-DOF airfoil system is presented and the effect of initial angle of attack on the dynamic instability are also shown.own.

• International Journal of Aeronautical and Space Sciences
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• 제9권1호
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• pp.111-120
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• 2008

A particle image velocimetry (PIV) technique was employed to investigate the effects of blowing jet on the flow characteristics over stationary and pitch-oscillating airfoils. The Reynolds number was $7.84{\times}10^5$ based on the chord length. It was found that for stationary airfoil cases, continuous and pulsating blowing jets successfully reduced separated wake region at high angles of attack. A comparison study of two different types of jet blowing indicated that pulsating jet is more effective than continuous jet for flow separation control. Pulsating leading-edge blowing postpones flow separation and increased stall angle of attack by $2^{\circ}{\sim}3^{\circ}$. For pitch-oscillating airfoil cases, the PIV results showed that blowing jet efficiently delays the separation onset point during pitch-up stroke, whereas it does not prevent flow separation during pitch-down stroke, even at angles of attack smaller than static ones.