자동차 후류에서 에어스포일러의 영향에 대한 PIV 측정

김성초,성재용,김정수,최종욱,김진석 대한기계학회 2006 大韓機械學會論文集B Vol.30 No.2

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.

SI 엔진의 스로틀 밸브에서 유동장 특성에 대한 실험해석

김성초,김철,최종근,이석정,Kim, Sungcho,Kim, Cheol,Choi, Jonggeun,Lee, Seokjeong 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.7

Experimental investigations on the flow characteristics of downstream region of a butterfly valve, which is used in SI engine, have been conducted according to Reynolds number and valve angle. Measurement programs of the flowfield using x-type of hotwire anemometry include the mean and fluctuating velocity, turbulnet intensity, shear stress, power spectrum and pressure loss coefficient. Experimental results show that flow characteristics and independent of relatively high Reynolds number; 60,000 and 80,000. It is also seen that streamwise mean velocities have relatively large velocity gradient around the butterfly valve with increasing the valve opening angle and this trend appears even in the far downstream region. The distributions of turbulent intensity and shear stress show irregular behavior regardless of the valve opening angle and those of the case of the valve opening angle of 45°are the largest. The pressure loss coefficient of the body surface of the throttle valve increases mildly with the increase of Reynolds number and increases rapidly with the reduction of the valve opening angle.

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.

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.

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.-

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.

SI 엔진의 스로틀 밸브에서 유동장 특성에 댜한 실험해석

김성초,김철,최종근,이석정 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.7

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.

비압축성 2차원 층류 유동에서 임계층에 대한 비선형 해석

김성초 순천대학교 공업기술연구소 1992 工業技術硏究所論文集 Vol.6 No.-

This describes the phenomena near the critical layer for the stratified laminar shear layer, the Rossby wave and the gravity wave based on the celebabted Orr-Sommerfeld(O-S) equation which expresses the stability of flow. It is possible to solve the O-S equation numerically provided that the velocity of main flow, and the initial and boundary conditions are given reasionably. However we can not easily find the physical meaning of the flow characteristics from those numerical solutions. So it is valuable to develop the mathematical perturbation solution procedure near the interesting region, i.e. the critical layer, though that is difficult and lengthy. The stability of the stratified shear layer depends on the Richardson number(Ri), and Ri is 1/4 at the neutral state. The small disturbance(ε) forced in the stratified shear layer has the nonlinearity with the time scale of O[(1/4-Ri)^(-1)] and its time scale is O(ε^(-4/7)). When the oscillation of the periodic function is forced, the discontinuity in the vorticity occurred near the critical layer is O(ε^(1/2)). The critical layer in the gravity wave, │y│《1, absorbs, reflects or transmits the wave energy according to the wave number and Richardson number. Eventually, we should analyze numerically the O-S equation for the specified flow because it is difficult to find the general solution of it. The time scale etc. based on the theoretical analysis and experiments is necessary to find out the transition phenomena which is unsteady state.