• 대한기계학회논문집B
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• 제38권3호
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• pp.203-210
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• 2014

본 연구는 Weis-Fogh형 수차의 유체역학적 특성을 개선 와법으로 수치계산한 것이다. 날개(NACA0010에어포일)와 양쪽 수로 벽은 소스(Source) 및 볼텍스 판넬로 근사하였고, 자유 볼텍스는 각 물체 전체표면에서 도입하였다. 타임스텝마다 날개를 이동시켜가며 본 수차의 유동장 즉 비정상 속도장과 압력장을 계산하였다. 계산변수로는 주요 설계인자인 날개 뒷전에서 날개 축까지의 거리, 수로 폭 및 최대 열림각으로 하였다. 본 수차의 1매의 날개에 대한 최대 효율 및 출력계수는 속도비 U/V=2.0에서 각각 26% 및 0.4였다. 본 수차의 유동장은 날개가 수로 내에서 비정상적으로 움직이기 때문에 매우 복잡하다. 그러나 개선 와법을 이용하여 명확하게 계산할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.518-523
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• 2001

Vortex methods were originally conceived as a tool to model the evolution of unsteady, incompressible, high Reynolds number flows of engineering interest. Recently various methods have been proposed for simulating the diffusion in vortex methods for two-dimensional incompressible flows. We test the diffusion schemes of vortex methods. In this paper we directly compare the particle strength exchange scheme with the vorticity redistribution scheme in tenus of their accuracy and computational efficiency. Comparisons between both viscous models described are presented for short-time runs of impulsively started flows past a circular cylinder for Reynolds number of 60. The particle strength exchange scheme has been shown more accurate and efficient than the vorticity redistribution scheme.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1407-1412
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• 2004

The velocity and pressure fields of a ship's propulsion mechanism of Weis-Fogh type are studied by advanced vortex method. The wing of NACA0010 type and the channel are approximated by a finite of source and vortex panels, and the free vortices are introduced from the surface of their bodies. The viscous diffusion of fluid is represented by the core-spreading method. The velocity field is calculated on the basis of Biot-Savart law and the pressure field is calculated from the integration equation formulated by Uhlman. The flow fields of this propulsion mechanism are unsteady and complex, but the flow fields are clarified by numerical simulation.

• 대한기계학회논문집B
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• 제22권8호
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• pp.1041-1051
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• 1998

The fluid dynamic properties of a circular arc type sea anchor were calculated by a discrete vortex method. The flow for the surface of the sea anchor was represented by arranging bound vortices at adequate intervals. The simulations were performed by assuming that the separations occur at edges. With time, the drag coefficient was almost constant but the lift coefficient oscillated in a cycle by von Karman's vortex street. As the camber ratios increase, the drag coefficient and Strouhal number were almost constant but the oscillating amplitude of the lift coefficient increased largely.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.345-348
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• 2002

The Flow patterns around two cylinders in various arrangements were studied by a discrete vortex method. The flow for the surface of each cylinder was represented by arranging bound vortices at adequate intervals. The viscous diffusion of fluid was represented by the random walk method. The vortex distributions, streaklines, timelines and velocity vectors around two cylinders were calculated for centre-to-centre pitch ratios of $P/D=1.5 and 2.5$, attack angles of ${\alpha}=0^{\circ},\;30^{\circ},\;60^{\circ}\;and\;90^{\circ}$, and Reynolds number of Re=1200. The results of simulation correspond to the photographs by flow visualization and the flow intereference between two cylinders in various arrangements was clearly visualized by a numerical simulation.

• Journal of Advanced Marine Engineering and Technology
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• 제27권3호
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• pp.365-372
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• 2003

The Flow patterns around two cylinders in various arrangements were studied by a discrete vortex method. The flow for the surface of each cylinder was represented by arranging bound vortices at adequate intervals. The viscous diffusion of fluid was represented by the random walk method. The vortex distributions. streaklines. timelines and velocity vectors around two cylinders were calculated for centre-to-centre pitch ratios of P/D=1.5 and 2.5, attack ang1es of $a=0^{circ}, 30^{circ}, 60^{circ} and 90^{\circ}$. and Reynolds number of Re= 1200. The results of simulation correspond to the photographs by flow visualization and the flow intereference between two cylinders in various arrangements were clearly visualized by a numerical simulation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1601-1606
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• 2004

In this paper, the unsteady behavior of the viscous flow field past an impulsively started elliptic cylinder is studied numerically. In order to analyze flow field, we introduce vortex particle method. The vorticity transport equation is solved by fractional step algorithm which splits into convection term and diffusion term. The convection term is calculated with Biot-Savart law, the no-through boundary condition is employed on solid boundaries. The diffusion term is modified based on the scheme of particle strength exchange. The particle redistributed scheme for general geometry is adapted. The flows around an elliptic cylinder are investigated for various attack angles at Reynolds number 200. The comparison between numerical results of present study and experimental data shows good agreements.

• 대한기계학회논문집B
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• 제32권6호
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• pp.421-428
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• 2008

In this paper, we investigated the flow of an incompressible viscous fluid past a sphere which is oscillated one-dimensionally over flow regimes including laminar flow at Reynolds number of 100, 200 and Strouhal number of up to 5000. In order to analyze flow and estimate critical Strouhal number, we introduce three-dimensional vortex element method. With this method, separation only appears in decreasing velocity region during the high Strouhal numbers. We find out that vorticity distribution around sphere is proportionl to the Strouhal number. And we can decide that low Strouhal number is below 100, high Strouhal number is above 500 from many results. Thus the critical Strouhal number(St) effected to the flow field is expected to be 100

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.63-66
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• 2002

The Flow patterns around two cylinders in various arrangements were studied by a discrete vortex method. The flow for the surface of each cylinder was represented by arranging bound vortices at adequate intervals. The viscous diffusion of fluid was represented by the random walk method. The vortex distributions, streaklines, timelines and velocity vectors around two cylinders were calculated for centre-to-centre pitch rations of P/D=1.5 and 2.5, attack angles of $\alpha=0^{\circ},\;30^{\circ},\;60^{\circ},\;and\;90^{\circ}$, correspond to the photographs by flow visualization and the flow intereference between two cylinders in var ious arrangements was clearly visualized by a numerical simulation.

• 대한기계학회논문집B
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• 제28권7호
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• pp.771-779
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• 2004

Unsteady behavior of the early wake in the viscous flow field past an impulsively started semicircular cylinder is studied numerically. In this paper, we propose the hybrid diffusion scheme to simulate dynamic characteristics of wake such as a fishtail-like flapping and an alternate vortex-shedding more accurately. This diffusion scheme based on particle strength exchange is mixed with the stochastic nature of random walk method. Also, the viscous splitting algorithm which calculates convective and diffusion terms successively is applied in order to handle random walk method effectively. Consequently, the early behavior of wake due to the breakdown of symmetrical vortici balance is more practically simulated with the vortex particle method.