反應이 있는 亂流에서 擴酸, 消散 및 壓力- 速度의 相關關係 解析

金星初 順天大學校 1989 論文集 Vol.8 No.1

熱放出性이 큰 反應이 있는 亂流에서 變動포텐셜과 過度場 사이에 중요한 相關關係가 있는지 與否가 분명하지 않으며, 純粹한 過度動力學처럼 전통적인 亂流槪念을 적용할 수 있는지 조사해야 한다. 勾配擴散 模型은 반응이 있는 난류의 極端的인 해결 방법으로 적용은 간단하지만 모형 자체가 深刻한 誤差를 갖을 수 있으므로 火焰 및 燃燒形態에 따라서 適當히 修正되어야 한다. 또한 消散은 非壓縮性 흐름에 대한 경우와 비교해서 전적으로 새로운 形態를 갖을 수 있다. 壓力一速度의 相互作用은 燃燒器에서 처럼 壓力場이 一定하지 않은 때는 그렇지 않은 경우에 비교하여 다른 특성을 갖는다. 난류문제는 연소현상의 有無에 관계 없이 實驗,理論 또는 數値硏究에 많은 어려움이 있다. 즉, 거의 모든 自然現象이 난류현상임에도 불구하고 해석에 많은 가정이 따르고 현상마다 다르다. 한편, 電子計算器의 큰 발전과 數値解法의 개발로 많은 문제들이 해결되고 있으나 이에 앞서서 실험에 의한 자료 확보와 연구가 폭넓고 깊이 이루어져야 한다. In general, turbulent modellings agree well with the experimental results for the cold gas without exothermicity. However, they can not be applied to the turbulent reacting problems as it is. A concept of the gradient diffusion accepted in the turbulent reacting problems is very simple to use but contains large errors. And the form of reacting turbulent dissipation is very different from that in the cold gas cases. Pressure-velocity correlation is hard to measure experimentally and must be carefully dealt with in the flow field where the pressurd is not uniform, e.g.inside of combustor. This paper describes analytically based on the physical concept diffusion, dissipation and pressure-velocity correlation in the reacting turbulent flow.

단순화된 표시자-세포 방법으로 해석한 물방울이 자유 표면에 떨어질 때의 현상

김성초 順天大學校 1991 論文集 Vol.10 No.1

본 논문은 단순화된 표시자-세포 방법을 사용하여 한 방울의 액체가 그릇에 담긴 액체의 자유표면 중앙으로부터 약간 왼쪽에 떨어질 때의 현상을 해석하여 타당한 결과를 얻었다. 유동의 일반적인 현상(numerical visualization)과 유선, 와도 및 압력 분포를 구하였으며 압력 분포를 제외하고는 대략적으로 대칭적인 분포를 한다고 볼 수 있다. 특히 액체 방울이 그릇의 중앙으로부터 왼쪽으로 편향하여 떨어졌기 때문에 유선 등에서는 오른쪽 영역에서 흥미로운 현상들이 발견되었는데 이것이 관연 물리적으로 타당한지, 아니면 수치적 오차나 수치 계획의 오류에서 비롯한 것인지는 앞으로 규명해야 할 문제로 생각된다. 또한 액체 방울이 컵과 같이 축대칭인 자유 표면에 떨어지거나 호수처럼 무한 크기의 자유 표면에 떨어질 때의 현상과 낙하 속도의 영향, 액체 방울 크기의 영향 등도 해석해 볼 필요가 있을 것이다. This paper describes two-dimensional flow phenomna when a single droplet drops on the free surface of the fluid contained in the vessel. The marker and cell(MAC) method can successfully solve the free surface problems such as the surface wave, two droplets collision and the dropping droplet on the fluid contained vessel. The MAC method is somewhat inefficient since it solves all the primitive variavles, velocities and pressure, however the simplified marker and cell (SMAC) method, which is adopted in this study, is easy to use and its computation time is also short because it avoids solving the pressure terms directly. Both the MAC and SMAC method are characterized to be applied to the cells which constitute of thecalculation domain, and in which the massless particles exist. Since a droplet drops on the slightly left-hand side of the vessel center in this study, the flow patterns-streamlines, vorticities and pressure dustributions-of course loose a little the symmetricity. But they are similar one another after a droplet jumps into the fluid. Especialy it is interesting that many small vorticies are found in right part of the streamlines, and that the fluid surfaces well accord with the zero pressure lines at the same time level.

정렬 격자를 사용하여 유한 요소법으로 해석한 2 차원 스톡스 흐름

김성초 順天大學校 1998 論文集 Vol.17 No.1

This paper describes the procedure of the finite element method to simulate the two-dimensional flow field. The mesh is adopted by using the structure grid system generated around the circular cylinder and inside the t-type channel. The convective acceleration terms in the momentum equations are neglected under the Stokes flow assumption. Thus the separated wake over the circular cylinder does not appear, however, on the other hand the calculation results are shown to be reasonable for the low Reynolds number. The time derivative term is expressed by both the Euler method and the relaxation method. Since the described method cannot analyze the pressure somewhat accurately, the different scheme such as the predictor and corrector method, which finds the pressure implicitly, and more effective matrix operation method need to be considered later.

3차원 와 격자 해석에 의한 날개의 공기역학적 특성

김성초 순천대학교 공업기술연구소 1993 工業技術硏究所論文集 Vol.7 No.-

This paper analyzes the aerodynamic characteristics of the various wings using the vortex lattice method(VLM) based on the potential flow theory. VLM calculates the lift coefficient and its slope with respect to the angle of attack(a) for the various shape of wing and aspect ration(AR), i.e., forward or backward swept wings, tapered wings and delta wings. The numerical results agree well with the existing experimental ones in the favorable range of angle of attack, however the discrepancy between them is caused by the real fluid properties. VLM can be easily extended to analyze the aerodynamic characteristics of geometrically complex three-dimensional bodies such as airplanes, cars and so on.

2次元 直角空洞의 壁壓力 및 剝離 剪斷層의 特性

김성초 順天大學校 1990 論文集 Vol.9 No.1

The pressure distribution on the 2-dimentional rectangular cavity wall and the velocity of the separated turbulent shear layer are measureed by varying the cavity depth and Raynols number based on cavity width and freestream velocity. The behavior of the pressure distribution on the wall is characterized by the lower pressure near the center of walls and bottom and the high pressures at the corner, as well as the hightest pressure at the reattachment corner. Based upoon the experimentally measured velocity profile the intergral constants of the analytical jet flow are determined, and found that the upstream free shear layer may be assumed as plane jet and its velocity can be predicted by Prandtl's mixing length theory. The autospectrum in the separated shear layer follows the-5/3 power law generally not depending upon the cavity depth and Reynolds number(Re).

品質시스템의 最適化에 關한 硏究

金星初 단국대학교 경영대학원 1982 經院論叢(壇國大學校) Vol.2 No.-

패널 방법과 불연속 와류 입자방법에 의한 2차원 무딘 물체 주위의 비정상 공력 해석

김성초 순천대학교 공업기술연구소 1998 工業技術硏究所論文集 Vol.12 No.-

This paper describes the describes the discrete vortex method to solve a two-dimensional incompressible flow field around bluff bodies such as triangle and square prisms. This method is combines with the panel method since the governing equation is reduced to Laplace equation. Vortices generated from the known separation points are mathematically treated by a solid and free vortex model with introducing a cut-off radius. And the exponential type of vortex diffusion is assumed. Reynolds numbers are 12400 and 17500, and angles of attack are o° and 5° for triangle and square prisms, respectively. The Strouhal numbers characterizing the vortex shedding rate are 0.138 and 0.123, and the drag coefficients are 2.3 and 2.1 for triangle and square prisms, respectively. Thus the computational results are reasonably acceptable comparing with experimental ones. In addition, the position of wake vortices shed from the separation points are traced.

유한 요소법에 의한 비압축성 직각공동 흐름 해석

김성초 순천대학교 공업기술연구소 1997 工業技術硏究所論文集 Vol.11 No.-

This paper describes the finite element method procedures, so called the Courant method, which combines the Ritz method and the least square concept. The interpolation function is simply linear. The test geometry is a square cavity and the rectangular elements are adopted with concentrating the grids near the wall surfaces. The whole grid system of 41×41 is generated by the transfinite interpolation. And Reynolds number based on the cavity width is 12000, and so the flow is considered as laminar. The finite element procedure is successful and the typical results are obtained such as velocity vector field, streamlines, confined and two corner vortices, and pressure field. Especially, the x-direction velocity agrees well with the experimental result.

원통 주위의 비정상 비압축성 층류 흐름의 수치해석

김성초 順天大學校 1997 論文集 Vol.16 No.1

This paper describes the marker-and-cell method(MAC) to calculate two-dimensional unsteady laminar flow around the circular cylinder. The governing equations are expressed in the conservative forms and the pressure field is evaluated by the Poisson equation with the successive over-relaxation method. The grid system is generated simply by the conformal mapping function and the primitive physical variables are computed at the different cell points, i.e., the grids are staggered. It is found that this numerical procedures is successful to solve the unsteady and separated flow occurred around the blunt body. The numerical results show the pressure, velocity vector and streamline distributions, and ad hoc the confined and shedding vortices behind a circular cylinder. There is periodic behavior in lift coefficient, however, drag characteristics has no strong periodicity.

라이트힐의 역방법을 사용한 아음속 익형 설계

김성초 순천대학교 공업기술연구소 1991 工業技術硏究所論文集 Vol.5 No.-

This paper describes the design procedures on the subsonic airfoil using Lighthill's inverse method. The inverse method adopts the specified velocity distributions on the airfoil surface to design the airfoil geometry. On the other hand, the direct method calculates the velocity distribution from the given airfoil shape. The former needs to be specified the velocity characteristics based on the physical phenomena. Thus it is necessary to devide the airfoil into some segments, which is generally consisted of the leading and the trailing edge parts, and the velocity decay regions on the upper and lower surfaces. The design parameters related to the airfoil shape are the numbers of leading and trailing edge segments(n, m), the locations of velocity decays (TU's, TL's), their rates(0 in this calculation), the design angles of the upper and lower surfaces(α_1, α_2), and the rear loading(b). The essential concept of the airfoil design is to obatin the large lift and to alleviate or eliminate the flow boundary layer. For the purpose of them, the various physical devices are adopted. When the abovementioned design parameters are carefully changed, however, the optimal airfoil can be generated easily and fastly without the physical devices.