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예조건화된 Navier-Stokes 방정식에서의 풍상차분법의 수치특성
길재흥,이두환,손덕영,최윤호,권장혁,이승수,Gill, Jae-Heung,Lee, Du-Hwan,Sohn, Duk-Young,Choi, Yun-Ho,Kwon, Jang-Hyuk,Lee, Seung-Soo 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.8
Numerical characteristics of implicit upwind schemes, such as upwind ADI, line Gauss-Seidel (LGS) and point Gauss-Seidel (LU) algorithms, for Navier-Stokes equations have been investigated. Time-derivative preconditioning method was applied for efficient convergence at low Mach/Reynolds number regime as well as at large grid aspect ratios. All the algorithms were expressed in approximate factorization form and von Neumann stability analysis was performed to identify stability characteristics of the above algorithms in the presence of high grid aspect ratios. Stability analysis showed that for high aspect ratio computations, the ADI and LGS algorithms showed efficient damping effect up to moderate aspect ratio if we adopt viscous preconditioning based on min-CFL/max-VNN time-step definition. The LU algorithm, on the other hand, showed serious deterioration in stability characteristics as the grid aspect ratio increases. Computations for several practical applications also verified these results.
예조건화된 압축성유동 수치기법에서의 풍상차분법의 수치특성 검토
길재흥(J. H. Gill),이두환(D. H. Lee),최윤호(Y. H. Choi),권장혁(J. H. Kwon),이승수(S. S. Lee) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
Studies of the numerical characteristics of implicit upwind. schemes, such as upwind ADI, Line Gauss-Seidel(LGS) and Point Gauss-Seidel(LU) algorithms, for preconditioned Navier-Stokes equations are performed. All the algorithms are expressed in approximate factorization form and Van Neumann stability analysis and convergence studies are made. Preconditioning is applied for efficient convergence at low Mach numbers and low Reynolds numbers. For high aspect ratio computations, the ADI and LGS algorithms show efficient and uniform convergence up to moderate aspect ratio if we adopt viscous preconditioning based on min-CFL/max-VNN time-step definition. The LU algorithm, on the other hand, shows serious deterioration in convergence rate as the grid aspect ratio increases. Computations for practical applications also verify these results.
압축성 유동 해석을 위한 압력 기반 해석자의 개선된 알고리즘 개발
김태우,길재흥 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.4
In this paper, an improved pressure-based computational fluid dynamics algorithm for numerical analysis of compressible flow with shock waves was described. For this purpose, the Kurganov-Tadmor flux splitting scheme, which is mainly used in density-based solvers, was applied to a developed pressure-based solver and a verification analysis of compressible flow problems were performed using the developed solver. It was confirmed that the developed solver had the similar analytical ability with that of the other numerical codes through the analysis of the 2D oblique shock wave and the backward-facing step problem in the supersonic flow region. In order to verify the analytical ability for the transonic flow region of the developed solver, 2D RAE2822 airfoil and 3D Onera M6 wing were analyzed and compared with results of experiments and other numerical analysis codes. It is confirmed that the analytical ability of developed solver in the high speed flow region such as supersonic and transonic is somewhat improved than the commercial analysis package and is similar to the density based in-house CFD code.
오픈 소스(OpenFOAM)에 기반한 공력해석 전용 프로그램(ISAAC) 개발
김병윤,길재흥,신훈범 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.11
항공기 공력 예측 방법들 중 전산유체역학을 이용한 3차원 해석 방법의 중요성이 증가하고 있으며, 해석결과의 정확성 및 해석 과정의 효율성이 강조되고 있다. 본 연구에서는 범용성, 폐쇄성, 고비용을 특징으로 하는 상용프로그램의 한계를 극복하기 위해 오픈 소스(OpenFOAM)를 기반으로 공력해석 전용 프로그램을 개발하였다. 개발 프로그램은 내재적 기법의 압축성 유동과 공력해석에 최적화된 전/후처리 기능을 포함하고 그래픽과 텍스트 기반의 사용자 환경을 포함하고 있다. 격자의 생성은 오픈폼에서 제공하는 snappyHexMesh를 이용하였으며 마하수 및 받음각의 변화에 따른 계산을 한 번에 처리할 수 있도록 하였으며, 후처리 단계에서는 개발자가 필요로 하는 공력 데이터들을 자동으로 도출해 낼 수 있도록 개발하여 연구개발의 효율성을 높일 수 있게 되었다. To predict aerodynamic forces of aircraft, dependency on three dimensional CFD analysis are growing. And the accuracy and efficiency of CFD results became more important. Many CFD engineers in industries are using commercial CFD packages. Commercial packages have some limits - can"t access to the source code, general purpose program and high cost. So in this research we developed aerodynamics oriented CFD program based on open source S/W, OpenFOAM to overcome the limits of commercial packages. Developed program, ISAAC is composed of flow solver, pre/post processing and graphic/text user interface. To create mesh we used snappyHexMesh utility of OpenFOAM. Many simulations of angle of attack sweep and Mach number sweep can be run at one time. To improve post processing efficiency, we made program to get the aerodynamic data and graphs automatically.
공기청정 시스템 성능예측을 위한 실내 유동현상에 관한 수치모사
손덕영,이두환,길재흥,최윤호,김동현 한국에너지학회 2002 에너지공학 Vol.11 No.4
본 연구에서는 공기청정기의 최적설계에 필요한 자료를 획득하기 위해 다양한 실내공간에서의 유동에 대한 연구를 수치해석적인 방법으로 수행하였다. 실내유동 해석을 위해서 사용된 공기청정기의 사용처로는 물류창고, 아파트 거실과 주방, 6인 병실을 선정하여 계산을 수행하였다 시간에 따른 평균농도 변화는 모든 실내공간에서 완전 혼합(perfect mixing)인 경우와 매우 흡사하게 나타나는 것을 볼 수 있었고, 공기청정기의 설치 위치가 시간에 따른 실내의 평균농도 변화에 미치는 영향은 미미한 것을 볼 수 있었다. 실내의 국부적인 농도를 살펴보면 사용처 별로 유동의 흐름이 원활하지 못해서 생기는 공기정화 취약구 역을 관찰할 수 있었으며, 이는 각 공간모델과 공기청정기의 설치위치에 따라 크게 달라지는 것을 볼 수 있었다. ln this paper, flowfields inside the various rooms have been investigated. A storage room, a liv-ingroom with a kitchen in an apartment, and a hospital room are considered in the present calculations. In all cases, it was found that the average of air change rate is. similar to that of perfect mixing assumption and the location of air purifier has little effects on the average air change rate. Detailed local air concentrations show that there are regions where air is not quite purified because of non-uniform circulation of air flow. The location of air purifier has great effects on this behavior.
오픈폼을 활용한 자유진동하는 라이저 주위 유동의 LES 해석
정재환,정광열,길재흥,정동호 한국해양공학회 2019 韓國海洋工學會誌 Vol.33 No.5
In this study, the free motion of a riser due to vortex shedding was numerically simulated with Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. A numerical simulation program was developed by applying the Rhie-Chow interpolation method to the pressure correction of the OpenFOAM standard solver pimpleDyMFoam. To verify the developed program, the vortex shedding around the fixed riser at Re = 3900 was calculated, and the results were compared with the existing experimental and numerical data. Moreover, the vortex-induced vibration of a riser supported by a linear spring was numerically simulated while varying the spring constant. The results are compared with published direct numerical simulation (DNS) results. The present calculation results show that the numerical method is appropriate for simulating the vortex-induced motion of a riser, including lock-in phenomena.
전산유체역학을 이용한 370 km/h 이상 고속열차의 공기역학 특성 연구
김나영,김범수,길재흥,안준선,권혁빈 한국철도학회 2023 한국철도학회논문집 Vol.26 No.12
Speeds of railways are increasing, expanding to over 370 km/h, exceeding Mach number 0.3, beyond which the compression effect of air cannot be ignored. In this study, computational fluid dynamics have been employed to analyze the flow field around the EMU-320 train by changing the train speed from 300 km/h to 430 km/h to analyze changes in aerodynamic characteristics as speed increased. The results show that the aerodynamic drag coefficient (C D ) changed up to 0.83% by the compromising effect of the increase in pressure drag due to the air compressibility effect and the decrease in friction drag due to the increase in Reynolds number. The coefficient of peak-to-peak pressure change during nose passes (C p,max ) increased by up to 4.86%, which means that it is dominated by the air compressibility effect. The leeward rail moment coefficient (CM x,lee ) in crosswind condition increased by only 0.64%, showing that this value is almost unaffected by the air compressibility effect.