• 한국항공우주학회지
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• 제30권8호
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• pp.37-45
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• 2002

본 연구에서는 이차원에서 비정상 비점성 유동해석을 위한 비정렬 동적 편자 기법을 개발하였다. 유동해석 기법은 시간에 대해 2차의 정확도를 갖는 내재적인 시간적분법을 사용하였으며, 격자중심의 유한 체적법과 Roe의 풍상차분법을 이용하여 공간에 대한 차분화를 하였다. 시간과 공간에 대한 정확도를 증가시키기 위해서는 해에 따라 원하는 위치에 격자점들을 임의로 추가할 수 있는 비정상 동적 적응격자 기법을 사용하였다. 이를 이용하여 이차원의 2자유도를 갖는 스프링 에어포일 시스템의 와류와의 간섭현상에 따른 공탄성적 변위를 예측하였다.

• 천문학회보
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• 제38권2호
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• pp.101.2-101.2
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• 2013

We present a new computational fluid dynamic (CFD) simulation code. The code employs the moving and polyhedral unstructured mesh scheme, which is known as a superior approach to the conventional SPH (smoothed particle hydrodynamics) and AMR (adaptive mesh refinement) schemes. The code first generates unstructured meshes by the Voronoi tessellation at every time step, and then solves the Riemann problem for surfaces of every Voronoi cell to update the hydrodynamic states as well as to move former generated meshes. For the second-order accuracy, the MUSCL-Hancock scheme is implemented. To increase efficiency for generating Voronoi tessellation we also develop the incremental expanding method, by which the CPU time is turned out to be just proportional to the number of particles, i.e., O(N). We will discuss the applications of our code in the context of cosmological simulations as well as numerical experiments for galaxy formation.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.57-70
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• 2008

A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.57-70
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• 2008

A high-order accurate Euler flow solver based on a discontinuous Galerkin finite-element method has been developed for the numerical simulations of blade-vortex interaction phenomena on unstructured meshes. A free vortex in freestream was investigated to assess the vortex-preserving property and the accuracy of the present flow solver. Blade-vortex interaction problems in subsonic and transonic freestreams were simulated by adopting a multi-level solution-adaptive dynamic mesh refinement/coarsening technique. The results were compared with those of other numerical and experimental methods. It was shown that the present discontinuous Galerkin flow solver can preserve the vortex structure for significantly longer vortex convection time and can accurately capture the complex unsteady blade-vortex interaction flows, including generation and propagation of acoustic waves.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.146-152
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• 2000

Two and Three dimensional dynamic adaptation code is developed for transient computations. This code involves mesh refinement and coarsening to either add points in high gradient regions of flow or remove points where they are not needed, for high spatial accuracy. Temporary cell algorithm is used to maintain the original grid quality. To show the assessment of the accuracy and efficiency, two dimensional study and unsteady flows are computed. Also, three dimensional steady computations are made to assess the refinement using temporary cell algorithm. The result shows the high spatial accuracy primarily in discontinuity regions in steady and unsteady computation.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.115-119
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• 2004

The effect of a continuous blowing or suction on an oscillating 2-D NACA0012 airfoil was investigated numerically for the dynamic stall control. The influence of control parameter variation was also studied in the view point of aerodynamic characteristics. The result showed that the blowing control kept a higher lift drag ratio before stall angle but the dynamic stall angle was not exceed to without control result. As the slot position was closer to leading edge, the positive control effect becomes greater. The stronger jet and the smaller jet angel made more favorable roles on the control performance. In the cases of the suction, the overall control features were similar to those of the blowing, but dynamic stall angle was increased, i.e. suction was more effective to control dynamic stall. It was also founded that the suction control was showed better control effect as the slot position moves to trail edge within thirty percentage of chord length. In the simulation for the jet strength and the jet angle control, the same tendencies were observed to those of blowing cases.

• 한국항공우주학회지
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• 제30권2호
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• pp.1-11
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• 2002

본 연구에서는 특별히 PC cluster와 같은 병렬 환경에서 효율적인 계산을 수행할 수 있는 격자중심에 기초한 직접모사 기법을 개발하였다. 병렬환경 하에서의 효과적인 계산 수행을 위해서는 전체 계산 영역을 격자수와 각 격자에 할당되는 모사 입자 수를 고려한 부 영역들로 나누어주었다. 또한, 격자 사용의 효율성 증대를 위해서는 매우 성긴 격자에서부터 출발하여 점차적인 격자 적응을 수행하였다. 본 방법은 2차원의 초음속 평판 문제와 축대칭의 Rothe, 노즐 문제에 적용하였다. 그 결과로부터 본 방법을 사용하면 기존의 입자 중심 기법에 비해 매우 효율적으로 희박기체 유동을 해석할 수 있음을 알 수 있었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.534-541
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• 2010

A high-order accurate Euler flow solver based on a discontinuous Galerkin method has been developed for the numerical simulation of unsteady flows on unstructured meshes. A multi-level solution-adaptive mesh refinement/coarsening technique was adopted to enhance the resolution of numerical solutions efficiently by increasing mesh density in the high-gradient region. An acoustic wave scattering problem was investigated to assess the accuracy of the present discontinuous Galerkin solver, and a supersonic flow in a wind tunnel with a forward facing step was simulated by using the adaptive mesh refinement technique. It was shown that the present discontinuous Galerkin flow solver can capture unsteady flows including the propagation and scattering of the acoustic waves as well as the strong shock waves.

• 한국항공우주학회지
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• 제30권8호
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• pp.46-55
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• 2002

본 연구에서는 저가형 PC-클러스터 환경에서 운영 가능한 고속 병렬처리 기법을 활용하여 전기체 항공기 및 발사체 형상을 고려할 수 있는 천음속/초음속 비선형 플러터 해석시스템을 개발하였다. 이는 이론적으로 진보된 수치해석 기법인 전산구조동역학(CSD), 유한요소법(FEM) 및 전산유체역학(CFD) 기법을 동시에 연계하고 있으며, 각종 비행체의 공탄성안정성 설계 과정에서 공학적으로 매우 정밀한 데이터 제공이 가능하다. 개발된 공탄성 해석시스템의 뛰어난 응용성을 보이기 위해 국내에서 개발 중인 초음속 항공기의 전기체 형상에 대해 천음속/초음속 비선형 공탄성 해석을 수행하였다.

• 대한조선학회논문집
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• 제45권5호
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• pp.477-486
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• 2008

Numerical analysis for slamming impact phenomena has been carried out when 2-dimensional wedge shaped structure with finite deadrise angles enter the free surface by using a commertial CFD code, FLUENT. Fluid is assumed incompressible and entry speed of the structure is kept constant. Geo-reconstruct scheme (or PLIC-VOF scheme) is used for the tracking of the deforming free surface. User defined function of 6 degrees of freedom motion and moving dynamic mesh option are used for the expression of the downward motion of the structure and deforming of unstructured meshes adjacent to the structure. The magnitude and the location of impact pressure and the total drag force which is the summation of pressures distributed at the bottom of the structure are analyzed. Results of the analysis show good agreement with the results of similarity solution, asymptotic solution and the solution of BEM.