• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.138-144
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• 1998

The BGK equation, which is the kinetic model equation of Boltzmann equation, is solved using FDDO(finite difference with the discrete-ordinate method) to compute the rarefied flow of monatomic gas. Using reduced velocity distribution and discrete ordinate method, the scalar equation is transformed into a system of hyperbolic equations. High resolution ENO(Essentially Non-Oscillatory) scheme based on Harten-Yee's MFA(Modified Flux Approach) method with Strang-type explicit time integration is applied to solve the system equations. The calculated results are well compared with the experimental density field of NACA0012 airfoil, validating the developed computer code. Next. the computed results of circular cylinder flow for various Knudsen numbers are compared with the DSMC(Direct Simulation Monte Carlo) results by Vogenitz et al. The present scheme is found to be useful and efficient far the analysis of two-dimensional rarefied gas flows, especially in the transitional flow regime, when compared with the DSMC method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.29-37
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• 1997

An implicit viscous turbulent flow solver is developed for two-dimensional geometries on unstructured triangular meshes. The flux terms are discretized based on a cell-centered finite-volume formulation with the Roe's flux-difference splitting. The solution is advanced in time using an implicit backward-Euler time-stepping scheme. At each time step, the linear system of equations is approximately solved with the Gauss-Seidel relaxation scheme. The effect of turbulence effects is approximated with a standard $k-{\varepsilon}$ two-equation model which is solved separately from the mean flow equations using the same backward-Euler time integration scheme. The triangular meshes are generated using an advancing-front/layer technique. Validations are made for flows over the NACA0012 airfoil and the Douglas 3-element airfoil. Good agreements are obtained between the numerical results and the experiment.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.30-40
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• 2007

The implicit discontinuous Galerkin method for the two-dimensional Euler equations was developed on unstructured triangular meshes, which can achieve higher-order accuracy by wing hierachical basis functions based on Legendre polynomials. Numerical tests were conducted to estimate the convergence order of numerical solutions to the Ringleb flow and the supersonic vortex flow for which analytic solutions are available. And, the flows around a circle and a NACA0012 airfoil was also numerically simulated. Numerical results show that the implicit discontinuous Galerkin methods with higher-order representation of curved solid boundaries can be an efficient higher-order method to obtain very accurate numerical solutions on unstructured meshes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.491-496
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• 2000

The objective of this study is to increase lift and decrease drag of an airfoil by delaying flow separation with piezo-ceramic actuators. The airfoil used is NACA 0012 and the chord length is 30cm. An experiment is performed at the freestream velocity of 15m/s at which the Reynolds number is $3{\times}10^5$. Seven rectangular actuators are attached to the airfoil surface and move up and down based on the electric signal. At the attack angle of $16^{\circ}$, the separation point is delayed downstream due to momentum addition induced by the movement of the actuators. Drag and lift are measured using an in-house 2-dimensional load cell and the surface pressures are also measured. Lift is increased by 10%, drag is reduced by 50%, and the efficiency is increased to 170%. The flow fields with and without control are visualized using the smoke-wire and tuft techniques.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.353-358
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• 2013

Present paper deals with turbulence-airfoil interaction noise and mainly investigates the effects of airfoil thickness on the broadband noise spectrum. The acoustic power radiation from an airfoil is predicted using high-order time-domain method, which is based on the computational aeroacoustic technique solving the linear Euler equations. The homogeneous and isotropic turbulence is generated by utilizing the synthetic turbulence modeling based on random particle method. The airfoils taken into consideration are a flat-plate and a NACA0012 airfoil aligned with uniform mean flow. The effects of airfoil thickness on the radiated inflow turbulence noise are investigated by comparing acoustic power spectrum predicted for each airfoil. The comparison of acoustic power spectrum reveals that the airfoil thickness significantly contributes the high frequency noise reduction.

• 한국가시화정보학회지
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• 제4권2호
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• pp.51-58
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• 2006

A boundary layer visualization was carried out in order to investigate the influence of Reynolds number on an oscillating airfoil. An NACA 0012 airfoil is sinusoidally pitched at the quarter chord point with oscillation amplitude of ${\pm}6^{\circ}$. A smoke-wire technique was employed to visualize the boundary layer and the near-wake. The freestream velocities are 1.98, 2.83 and 4.03m/s and corresponding chord Reynolds numbers are $2.3{\times}10^4,\;3.3{\times}10^4$, and $4.8{\times}10^4$, respectively. As the reduced frequency of K=0.1 is fixed, the corresponding frequency of an airfoil was adjusted in each case. The results reveal that the point at which the shear stress in an unsteady boundary layer separation disappears does not correspond with the position of the breakdown of the boundary layer, and that the breakdown of the boundary layer occurs further downstream.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.544-549
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• 2014

임계마하수보다 큰 자유흐름 마하수에서는 충격파의 발생으로 인해 급격한 항력증가가 발생하므로, 임계마하수 증가는 고속 공기역학에서 중요한 분야로 다뤄지고 있다. Whitcomb R. T.에 의해 천음속영역에서 순항할 수 있는 초임계익형이 개발되었으나, 충격파 제어 기법들에 대한 실험적인 검증은 형상 제작의 어려움으로 인해 한계를 지닌다. 따라서 본 논문에서는 2D_Comp-2.1_P와 Prandtl-Glauert 압축성 보정식을 이용하여 NACA0012와 RAE2822의 임계마하수를 해석하고, 충격파 제어 장치 중 하나인 Bump를 RAE2822에 설치하여 임계마하수를 향상시키기 위한 연구를 수행하였다. 연구 결과 충격파를 압축파로 분산시켜 충격파의 강도를 약화시키고, 양항비의 4.7% 증가를 확인하였다. 따라서 Bump를 설계한 RAE2822가 기본 익형보다 높은 천음속 조건에서 효율적인 공력특성을 가지는 것을 확인하였다.

• EDISON SW 활용 경진대회 논문집
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• 제4회(2015년)
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• pp.627-631
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• 2015

유동 교란에 의하여 균일유동이 아닌 자유류가 항공기 날개 표면을 지나면 공력 계수들이 균일 자유류 유동과는 달라진다. 예를 들어, 항공기들의 편대 비행에서 앞의 항공기가 생성한 후류가 뒷 항공기에 영향을 주고, 두 개의 주익을 가지는 Tandem Wing 항공기의 경우 첫 번째 주익에서 발생된 후류가 두 번째 주익의 공력에 영향을 미친다. 본 연구는 NACA0012 익형의 앞쪽에 또 다른 익형을 배치하여 앞 쪽의 익형에서 발생한 후류가 뒤의 익형에 미치는 영향을 익형 사이의 거리에 따라 분석하였다. 앞쪽의 익형에서 발생한 압력계수와 뒤쪽에서 발생한 압력계수의 비교를 통해 후류의 효과가 어떤 영향을 끼치는지 확인 하였고, 두 익형 사이의 거리가 2c일 때 후류의 영향이 거의 없음을 확인 하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.125-130
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• 1999

A flowfields around a NACA0012 airfoil pitching about a 1/4 chord and plunging in vertical displacement are analyzed by solving two-dimensional compressible Navier-Stokes equations. A steady solution was solved first as a validation of the code used and the results were compared with experimental data. Then as a unsteady case, the oscillatory airfoil was solved to compare the results with experimental data. Oscillating rate of pitching and plunging motion was set to have analogy and the magnitude of plunging was set using the magnitude of pitching angle of attack. Finally combined pitching and plunging motion was solved to show the effect of 2 different types of oscillating motion of the airfoil.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.137-143
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• 1999

The unsteady transonic viscous flow has been analyzed over an oscillatory airfoil. The CSCM(Conservative Supra Characteristic Method) upwind flux difference splitting method and the iterative time marching scheme having first order accuracy in time and second to third order accuracy in space was applied on dynamic meshes. A steady flow field of Mach number 0.7 has been calculated for the verification of unsteady algorithm. The time-accurate unsteady calculations have been done for NACA 0012 airfoil oscillating around quarter chord about freestream Mach number 0.6 on dynamic meshes. The results have been compared with the AGARD Case 3 experimental data. The periodic characteristics have been compared with the experimental results.