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표면 와류 분포 방법을 이용한 아음속 풍동의 2차원 수축부 설계
金學奉 한국항공대학교 1986 論文集 Vol.24 No.-
A design method for the two-dimensional wind Tunnel contractions of finite length have been developed using surface vortex distribution method with given velocity distribution and contraction ratio. The integral eguation for the wall shape is solved by means of numerical and iterative method. Some design examples are presented to compare with other design methods. The results show that the present method may be used to design two-dimensional contracting duct with good exit velocity uniformity and with desired wall pressure gradient, duct length and contraction ratio.
비정열 격자계에서 타원형 방정식의 수치해석을 위한 다중격자 가속
김학봉 한국항공대학교 1998 論文集 Vol.36 No.-
The multigrid method have been considered the most effective, especially when used to solve strongly eliptic problems. Unstructured grids have evolved over the recent years as a very variable approach for modeling complex geometries since they have been found to be very efficient means of generating body-conforming grids for complex configurations. The complete lack of order in unstructured grids precludes any possibility of generating suceccessively coarser grids. In the present works, the fine grids are created by division of trangular coarser grid cells. Thus, the cell-tree data structure is used to retrace the parents of fine cells on the adapted grid, and these parent cells along with the cells in the unembeded region of the flow domain constitute the coarser grid of multigrid of multigrid. The edge-tree data structure is used to interpolate the residuals back and forth between the fine and casrser level grids, and hence the scheme avoids relatively complicated intergrid transfer algorithms imployed in the other multigrid schemes. The purpose of this works is to extend the multigrid techniques historically employed by structured grid algorithms to unstructured solvers to accelerate convergence rates of the elliptic equation solver that is based on a finite volume cell-centered approach.
김학봉 한국항공대학교 1993 論文集 Vol.31 No.-
본 수치해석 연구는 낮은 레이놀즈 수의 유동내 원형 실린더로 부터 박리된 한쪽의 전단층을 제어함으로써 와류방출과정의 극적인 변화에 관한 것이다. 유동의 제어는 주 원봉의 주위에 제어 봉인 매우 가는 원형봉을 설치함으로 이루어 진다. 물체와 그 후류 주위의 점성영역으로 축소된 다물체 계산영역내에서 제어된 와류방출과정이 FEM-FDM 혼합 수치해석 방법에 의하여 해석 되었다. 압력구속 조건으로 부터 구해지는 물체표면의 시가나종속 유량함수값을 이용하여 낮은 에이놀즈수의 비압축성 2차원 Navier--Stokes 방정식을 해석하는데 와도-유량함수 방정식을 사용하였다. 비교적 좁은 다물체 주위의 영역에서는 표준 Galerkin 유한요소법이 사용되었도 나머지 계산영역에서는 일반좌표계를 이용한 유한차분법을 사용하였다. 수치적으로 해석된 결과들로 부터 ㅓ제어봉의 직경과 위치등이 와류방출과정, 시간평균 또는 순간 양항력 및 와류방출 주기등의 변화에 미치는 효과를 시험하였다. 추가로 순간 와도장 및 유선과 같은 계산된 결과로 부터 박리된 전단층의 말림과 와동의 세기등, 전단층의 변화에 대하여 상세히 논의하였다. This numerical study deals with the dramatic change of the votex shedding process by controllng a shear layer spearted from a circular cylinder at low Raynolds number. The control of the flow is estabilished by introducing a fine circular cylinder (the control cylinder) in the neighbourhood of the main cylinder. Controlled vortex shedding process inn the multiply connected domain which is reduced to viscous region near the boldies and their wakes was analyzed by the FEM - FDM blending technique. The vorticity-streamfunction formulation was used to solve the incompressible Navier-Stokes kequations with the time dependent wall streamfunctions determined from the pressure constraint condition and far field streamfunctions from the integro-differential formulation by the Green's theorem. The standard Galerkin finite element method was used in the relatively small multiply connected subdomain and the finite difference method based on the general coodinate system in the rest of the computational domain. The nume-rically analyzed data was used to examine the effects on the alteration of the vortex shedding processes, the time mean and fluctuatng fluid forces, and the vortex shedding frequancy due to variation of the position and diameter of the control cylinder. Furthermore, such matter as the deformation of the shear layer, namely, the position and strength of the rolling-up of the separated shear layers, were discussed in detail based on the calculated results which are the instantaneous voricity field and streamlines.