• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.562-567
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• 2014

본 연구에서는 교육 및 연구를 위한 CFD 해석 프로그램인 EDISON_CFD를 이용하여 Symmetric airfoil(NACA0012)과 Cambered airfoil(NACA4412)의 뒷전 두께에 따른 공력 특성을 분석해보았다. Chord 길이의 0%, 1%, 2%, 3%, 4%에 해당하는 뒷전 두께를 가지는 Blunt trailing edge airfoil의 받음각에 따른 공력 특성을 비교 및 분석하고, 어떠한 장단점을 가지는지 확인하였다. 그 결과 Chord 길이의 1% 뒷전 두께를 가질 때를 제외하면 뒷전 두께가 두꺼워질수록 최대양력계수는 증가하였고, 양항비와 실속각은 감소하였다. 또한, 뒷전 두께가 두꺼워질수록 Symmetric airfoil에서는 받음각 $0^{\circ}$를 기준으로 양력곡선기울기가 증가하였고, Cambered airfoil에서는 전체적으로 양력계수가 증가함과 동시에 양력곡선기울기 또한 증가하는 것을 확인할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.119-129
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• 1990

In case that the body with a cusp crack is under uniform heat flow, thermal stress intensity factors are calculated by using boundary element method with linearized body force term. The crack surface is under insulated or fixed temperature condition and the types of crack are symmetric lip and airfoil cusps. Numerical values of thermal stress intensity factors for a Griffith crack and cusp cracks in infinite bodies are proved to be in good agreement within .+-.5% when compared with the previous numerical and exact solutions, respectively. The thermal stress intensity factors for symmetric lip and airfoil cusp cracks in finite bodies are calculated about various effective crack lengths, configuration parameters, and heat flow directions. With the same crack surface thermal boundary conditions, heat flow directions and crack lengths, there are no appreciable differences in variations of thermal stress intensity factors between symmetric lip and airfoil cusp cracks. The signs of thermal stress intensity factors for each cusp crack are changed with each crack surface thermal boundary condition.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.75-79
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• 2014

In the paper, a study on the analysis of the effects of trailing edge thickness on the aerodynamic characteristics of an airfoil is described. In this research, modification of the formula representing NACA symmetric airfoil is studied to change the airfoil shape with different trailing edge thickness of user's choice. According to the result of aerodynamic characteristics, as the trailing edge thickness increases the maximum lift coefficient increases while the lift-to-drag ratio decreases. In this paper flow calculation results are demonstrated and the analysis on those results and findings on the effects of non-zero thickness of trailing edge are suggested.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.286-294
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• 1988

The thermal stress intensity factors (TSIF's) for the cusp cracks such as hypocycloid crack, symmetric airfoil crack and symmetric lip crack are determined by using Bogdanoff's complex variable approaches in plane thermoplasticity. The results are expressed in terms of the periodic functions of the direction of uniform heat flow. The TSIF's are shown to be sensitive to both the direction of uniform heat flow and be thermal boundary conditions. It is also shown that Fourence's solutions for an insulated circular hole and Sih's solutions for an insulated Griffith crack are derived from the results of the stress and displacement fields for the hypocycloid crack and the TSIF's for the various cusp cracks, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.497-504
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• 1988

The steady state thermal stress intensity factors (TSIF's) are analyzed for hypocycloid, symmetric airfoil and symmetric lip type rigid inclusions embedded in infinite elastic solids, using Boganoff's complex variable approach in plane thermoplasticity. Two thermal conditions are considered, one with an uniform heat flow disturbed by an insulated rigid inclusion of cusp crack shape and the other with an uniform heat flow disturbed by a rigid inclusion of cusp crack shape with fixed boundary temperature. The tendencies of TSIF's for rigid inclusions of cusp crack shape are somewhat different from those of traction free cusp cracks. However, if k=-1, the non-dimensionalized TSIF's for rigid inclusions of cusp crack shape become those of traction free cusp cracks like the tendencies of the SIF's under mechanical loading conditions. The thermal stress and displacement components for a rigid circular inclusion of radius Ro are drived from the results of a hypocycloid crack type rigid inclusion.

• Journal of Wind Energy
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• v.4 no.2
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1161-1169
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• 2012

A numerical study has been conducted to investigate the aerodynamic characteristics and behavior of a wing-tip vortex around a three-dimensional symmetric wing (NACA0015) in the vicinity of the ground. The aerodynamic characteristics and the wing-tip vortex change as a wing approaches the ground as a result of two different phenomena: the ground effect and the Venturi effect. The ground effect increases lift and decreases drag whereas the Venturi effect generates negative lift and increases drag suddenly. A symmetric airfoil experiences both phenomena with respect to changes in the angle of attack. In the case of a NACA0015 airfoil, the Venturi effect is dominant at small angles of attack but the ground effect is dominant at large angles of attack. Interestingly, both phenomena can be observed at the 4 degree of angle of attack. The vortex core moves inside a wing when the wing experiences the Venturi effect, whereas the vortex core moves outward when the wing experiences the ground effect.

• Journal of computational fluids engineering
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• v.4 no.3
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• pp.44-51
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• 1999

A modified version of SST turbulence model is suggested to simulate unsteady separated flows over oscillating airfoils. The original SST model, which shows good performance in predicting various steady flows, often results in oscillatory behavior of aerodynamic loads in large separated flow regions. It is shown that this oscillatory behavior is due to the adoption of the absolute value of vorticity in generalizing the original model. As a remedy, a modification is made such that the vorticity in the original SST model is replaced by strain rate. The present model is verified for a mild separated airfoil flow at fixed angle of incidence and for unsteady flowfields about oscillating airfoils. The results are compared with BSL model and original SST model. It is illustrated that the present model gives a better agreement with the experimental results than other two models.

• Wind and Structures
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• v.32 no.3
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• pp.239-248
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• 2021

In this study, three airfoil families, NACA, FX and S, in each case three from each series with different shapes were investigated at different angles of attack using Computational Fluid Dynamics (CFD) method. To verify the CFD model, simulation results of the NACA 0012 airfoil was compared against the available experimental data and k-ω SST was used as the turbulence model. Lift coefficients, lift to drag ratios and pressure distributions around airfoils were obtained from the CFD simulations and compared each other. The simulations were performed at three Reynolds numbers, Re=2×105, 1×106and 2×106, and angle of attack was varied between -6 and 12 degrees. According to the results, similar lift coefficient values were obtained for symmetric airfoils reaching their maximum values at similar angles of attack. Maximum lift coefficients were obtained for FX 60-157 and S 4110 airfoils having lift coefficient values around 1.5 at Re=1×106 and 12 degrees of angle of attack. Flow separation occurred close to the leading edge of some airfoils at higher angles of attack, while some other airfoils were more successful in keeping the flow attached on the surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.670-676
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• 2007

A comparative study on ground boundary conditions for the airfoil in ground effect has been carried out. The objective of the present study is to clarify effects of the ground boundary conditions so that it will be helpful to analyse results of wind tunnel tests using the fixed ground board or the image method. A low Mach number preconditioned Navier-Stokes solver using the overlap grid method has been applied. It has been turned out that results with the symmetric boundary condition are almost the same to those with the moving boundary condition. Results with the fixed ground boundary show discrepancy to those with the moving boundary condition when flow separation on the ground board takes place.