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이희동(H. D. Lee),강희정(H. J. Kang),권오준(O. J. Kwon) 한국항공우주학회 2005 韓國航空宇宙學會誌 Vol.33 No.5
헬리콥터 초기 설계 단계에서는 형상 변화에 따른 공력 성능 변화를 예측하여 최적의 형상을 결정한다. 덮개꼬리로터에서는 공력성능 개선을 위해 블레이드와 덮개사이의 끝단간극, 블레이드 평면형, 그리고 블레이드 배치의 최적화가 필요하다. 본 연구에서는 비정렬 격자에 기초한 비점성 압축성 로터 유동 해석 코드를 이용하여 설계 초기 기본형상의 덮개꼬리로터에 대해 끝단간극, 블레이드 평면형, 그리고 블레이드 배치 등의 형상변화에 따른 공력 성능을 예측하고 그 특성을 파악하였다. In the early stage of helicopter design, an optimal configuration is usually determined after a numerous parametric study about the aerodynamic performance due to geometric variation. In order to improve the aerodynamic performance of a shrouded tail rotor, optimization of the tip clearance gap between blade and shroud, the blade planform shape, and the arrangement of blade spacing is required. In the present study, the aerodynamic performance characteristics of a shrouded tail rotor due to geometric variation was investigated by using an inviscid compressible unstructured mesh flow solver for rotary wings.
LCP 방법에 기반한 효율적인 고차정확도 불연속 갤러킨 기법 개발
이희동(H.D. Lee),권오준(O.J. Kwon) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.11
A high-order accurate Euler flow solver based on a LCP(lifting collocation penalty) formulation of discontinuous Galerkin methods has been developed on unstructured triangular meshes. Numerical tests were conducted to estimate the convergence order of numerical solutions and the numerical efficiency for the Ringleb flow where analytic solutions are available. The results were compared with those of conventional discontinuous Galerkin method.
비정렬 격자계에서 고차 정확도의 내재적 불연속 갤러킨 기법의 개발
이희동(H.D. Lee),권오준(O.J. Kwon) 한국전산유체공학회 2007 한국전산유체공학회지 Vol.12 No.3
An implicit discontinuous Galerkin method for the two-dimensional Euler equations was developed on unstructured triangular meshes. The method can achieve high-order spatial accuracy by using 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. Also, the flows around a 2-D circular cylinder and an NACA0012 airfoil were numerically simulated. The numerical results showed that the implicit discontinuous Galerkin methods couples with a high-order representation of curved solid boundaries can be an efficient method to obtain very accurate numerical solutions on unstructured meshes.
비정상 유동 해석을 위한 고차정확도 격자 적응 불연속 갤러킨 기법 개발
이희동(H.D. Lee),최재훈(J.H. Choi),권오준(O.J. Kwon) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
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.
비정렬 혼합 격자계에서 신속 격자 변형 기법을 이용한 비정상 점성 유동 해석
이희동(H.D. Lee),정문승(M.S. Jung),권오준(O.J. Kwon) 한국전산유체공학회 2009 한국전산유체공학회지 Vol.14 No.3
In the present study, a fast grid deformation technique has been incorporated into the unsteady compressible and incompressible viscous flow solvers on unstructured hybrid meshes. An algebraic method based on the basis decomposition of normal edge vector was used for the deformation of viscous elements, and a ball-vertex spring analogy was adopted for in viscid elements among several spring analogy methods due to its robustness. The present method was validated by comparing the results obtained from the grid deformation and the rigid motion of entire grids. Fish swimming motion of an NACA0012 airfoil and flapping wing motion of a generic fighter were also simulated to demonstrate the robustness of the present grid deformation technique.
비정렬 격자계에서의 물-기체 2상 유동해석코드 수치 기법 개선
이희동(H.D. Lee),정재준(J.J. Jeong),조형규(H.K. Cho),권오준(O.J. Kwon) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation of condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new numerical scheme to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function, a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the CUPID code.
비정렬 격자 기반의 물-기체 2상 유동해석기법에서의 압력기울기 재구성 방법
이희동(H.D. Lee),정재준(J.J. Jeong),조형규(H.K. Cho),권오준(O.J. Kwon) 한국전산유체공학회 2010 한국전산유체공학회지 Vol.15 No.2
A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation or condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure distribution that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new reconstruction method to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function, a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the CUPID code.
비정렬 혼합 격자계에서 격자 변형 기법을 이용한 비정상 점성 유동 수치 모사
이희동(H.D. Lee),정문승(M.S. Jung),권오준(O.J. Kwon) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.4
In the present study, a grid deformation technique has been incorporated into the unsteady compressible and incompressible viscous flow solvers on unstructured hybrid meshes. An algebraic method based on the basis decomposition of normal edge vector was used for the deformation of viscous elements, and a ball-vertex spring analogy was adopted for in viscid elements among several spring analogy methods due to its robustness. The present method was validated by comparing the results obtained from the grid deformation and the rigid motion of entire grids. Fish swimming motion of an NACA0012 airfoil and flapping wing motion of a generic fighter were simulated to demonstrate the robustness of the present grid deformation technique.