• 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.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.228-231
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• 2008

Flow fields of a transonic centrifugal compressor are calculated using the commercial CFD code, CFX-TASCflow. Due to the transonic inlet condition, interactions between the shock wave and boundary layers and between the shock wave and tip leakage vortices generate complex flow structures and extra losses. The calculated results show that strong secondary flows due to high curvature and high rotational speed of the impeller. And streamlines near suction surface show that strong radially upward flow develops after the shock between the leading edge locations of main blade and splitter.

• 대한조선학회지
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• 제27권2호
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• pp.1-12
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• 1990

선미후류에 포함된 보오텍스 시스템과 프로펠러와의 상호작용을 이론적으로 해석하여 유효반류를 계산하는 방법을 제안하였다. 선미주위의 복잡한 유동을 Poincare의 방정식을 사용하여 수학적으로 표시하였고 임의의 점에서의 교란속도를 물체 표면에 분포되어 있는 쏘오스 및 보오텍스에 의한 유기속도의 표면적분과 유체중 위치하는 쏘오스 및 보오텍스에 의한 유기속도의 체적적분의 함으로 표시하였다. 이 식으로부터 유효속도(effective velocity)를 유체중 보오텍스에 의한 유기속도의 체적적분으로 정의하였다. 유체중의 보오텍스의 위치와 세기는 불균일한 호칭속도(nominal velocity)분포에 포함되어 있는 보오텍스로부터 프로펠러가 작동할 때의 유선변화를 고려하여 보오텍스 운동역학(vortex dynamics)을 만족하도록 결정된다. 이론을 검증하기 위한 계산예로써 축대칭 전단류(shear flow)중 원판형 추진장치가 작동할 때 프로펠러에 의한 유선변화 모형을 변화시켜 유효속도를 계산하였고 양력판 이론에 의한 값과 비교하였다.

• International Journal of Vascular Biomedical Engineering
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• 제2권1호
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• pp.11-16
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• 2004

Both flow visualizations and computational fluid dynamics were performed to determine hemodynamics in a total cavopulmonary connection (TCPC) model for surgically correcting congenital heart defects. From magnetic resonance images, an anatomically correct glass model was fabricated to visualize steady flow. The total flow rates were 4, 6 and 8L/min and flow rates from SVC and IVC were 40:60. The flow split ratio between LPA and RPA was varied by 70:30, 60:40 and 50:50. A pressure-based finite-volume software was used to solve steady flow dynamics in TCPC models. Results showed that superior vena cava(SVC) and inferior vena cava(IVC) flow merged directly to the intra-atrial conduit, creating two large vortices. Significant swirl motions were observed in the intra-atrial conduit and pulmonary arteries. Flow collision or swirling flow resulted in energy loss in TCPC models. In addition, a large intra-atrial channel or a sharp bend in TCPC geometries could influence on energy losses. Energy conservation was efficient when flow rates in pulmonary branches were balanced. In order to increase energy efficiency in Fontan operations, it is necessary to remove a flow collision in the intra-atrial channel and a sharp bend in the pulmonary bifurcation.

• 공업화학
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• 제28권4호
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• pp.448-453
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• 2017

테일러 반응기에서 일어나는 유동의 변화를 전산유체역학을 이용하여 3차원 유동해석을 수행하였다. 테일러 유동은 레이놀즈 수의 증가에 따라 5개의 영역(순환 쿠에트 유동(CCF), 테일러 와류 유동(TVF), 물결 와류 유동(WVF), 변조 물결 와류 유동(MWVF), 난류 테일러 와류 유동(TTVF))으로 나뉘어지며, 각각의 영역에서의 유동 특성을 알아보았다. 각각의 영역에서 와류의 형상, 개수, 길이 등에 차이를 나타나며 바이패스 흐름에도 영향을 줌을 확인하였다. 그 결과 TVF, WVF, MWVF, TTVF 영역에서 테일러 와류가 발생하였다. 테일러 와류의 개수는 TVF 영역에서 가장 많으며 TTVF 영역에서 가장 적게 관찰되었다. 수치해석모델의 검증을 위하여 실험결과와 비교하였고, 실험결과 대비 해석결과가 잘 일치함을 나타내었다.

• 대한원격탐사학회지
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• 제30권6호
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• pp.755-767
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• 2014

본 연구에서는 LARIAC2 GIS 자료와 전산 유체 역학(CFD) 모델을 이용하여 미국 캘리포니아 주 Los Angeles의 두 지역(Wilshire blvd. & Carondelet and Broadway & $7^{th}$ St.)을 대상으로 수치 실험을 수행하였다. 두 지역의 상세 도시 대기 흐름의 특성을 조사하기 위해 건물 자료 구축 알고리즘을 통해 벡터 형식으로 제공되는 LARIAC2 GIS 자료로부터 건물 도메인 자료를 추출하였다. 추출한 자료를 CFD 모델 입력 자료로 사용하여, 각 지역의 오전과 오후의 주 풍향과 풍속에 대해 수치 실험을 수행하였다. 도시 지역 내에서는 건물에 의해 국소적인 2차 흐름이 발생하면서 유입류와 비교하였을 때, 풍향과 풍속의 차이가 두드러졌다. 유입류와 평행한 방향으로 형성된 도시 협곡에서는 채널링 효과가 나타나면서 풍속이 국지적으로 증가하였고, 수직인 방향으로 형성된 도시 협곡에서는 연직 방향으로 잘 발달한 소용돌이가 형성되었다. 도시 협곡을 이루지 않은 건물의 풍상측에서는 말편자 소용돌이가 지면 근처에서 형성되었고, 풍하측에서는 재순환 영역이 형성되었다. 이와 같은 2차 순환(도시 협곡 소용돌이, 말편자 소용돌이, 재순환 영역)이 형성된 구역에서는 지면 근처의 풍속이 크게 증가하였다. 평균 풍속과 풍향 변화율을 조사한 결과, 대체적으로 풍속 증가율이 높은 곳에서 풍향 변화율이 비교적 낮았고 풍속 감소율이 높은 곳에서는 풍향 변화율이 높게 나타났다.

• Tribology and Lubricants
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• 제36권4호
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• pp.193-198
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• 2020

Fluid film bearings are among the best devices used for overcoming friction and reducing wear. Surface texturing is a new surface treatment technique used for processing grooves and dimples on the lubricated surface, and it helps to minimize friction further and improve the wear resistance. In several studies, parallel surfaces, such as thrust bearings and mechanical face seals, have been investigated, but most sliding bearings have a convergent film shape. This paper presents the third part of a recent study and focuses on the effect of the groove shape on the lubrication performance of inclined slider bearings, following the two previous papers on the effects of the groove position and depth. We adopted the continuity and Navier - Stokes equations to conduct numerical analyses using FLUENT, which is a commercial computational fluid dynamics code. The groove shape adopted in the numerical analysis is rectangular and triangular, and its depth is varied. The results show that the streamlines, pressure distributions, and groove shape significantly influence the lubrication performance of the inclined slider bearing. For both shapes, the load-carrying capacity (LCC) is maximum near the groove depth, where vortices occur. In the shallow grooves, the LCC of the rectangular shape is higher, but in deeper grooves, that of the triangular shape is higher. The deeper the rectangular groove, the higher the decrease in the frictional force. The results of this study can be used as design data for various sliding bearings.

• Advances in aircraft and spacecraft science
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• 제10권3호
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• pp.203-222
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• 2023

The detonation combustion is a supersonic combustion process follows on shock wave oscillations in detonation tube. In this paper numerical studies are carried out combined effect of blockage ratio and spacing of obstacle on detonation wave propagation of hydrogen-air mixture in pulse detonation combustor. The deflagration to detonation transition of stoichiometric (ϕ=1)fuel-air mixture in channel has been analyzed for effect of blockage ratio (BR)=0.39, 0.51, 0.59, 0.71 with spacing of 2D and 3D. The reactive Navier-Stokes equation is used to solve the detonation wave propagation mechanism in Ansys Fluent platform. The result shows that fully developed detonation wave initiation regime is observed near smaller vortex generator ratio of BR=0.39 inside the combustor. The turbulent rate of reaction has also a great significance role for shock wave structure. However, vortices of rapid detonation wave are appears near thin boundary layer of each obstacle. Finally, detonation combustor demonstrates the superiority of pressure gain combustor with turbulent rate of reaction of 0.6 kg mol/m3 -s inside the detonation tube with obstacle spacing of 12 cm, this blockage enhanced the turbulence intensity and propulsive thrust. The successful detonation wave propagation speed is achieved in shortest possible time of 0.031s with a significance magnitude of 2349 m/s, which is higher than Chapman-Jouguet (C-J) velocity of 1848 m/s. Furthermore, stronger propulsive thrust force of 36.82 N is generated in pulse time of 0.031s.

• International Journal of Aeronautical and Space Sciences
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• 제10권2호
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• pp.52-62
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• 2009

A three-dimensional compressible Navier-Stokes solver, KFLOW, using overlapped grids has recently been developed to simulate unsteady flow phenomena over helicopter rotor blades. The blade-vortex interaction is predicted for a descending flight using measured blade deformation data. The effects of computational grid resolution and azimuth angle increments on airloads were examined, and computed airloads and vortex trajectories were compared with HART-II wind tunnel data. The current method predicts the BVI phenomena of blade airloads reasonably well. It is found from the present study that a peculiar distribution of vorticity of tip vortices in an approximate azimuth angle range of 90 to 180 degrees can be explained by physics of the shear-layer interaction as well as the dissipation of numerical schemes.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.395-397
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• 2006

Air interlacing serves to protect the yarn against damage, strengthens inter-filament compactness or cohesion, and ensures fabric consistency. The air interlacing nozzle is used to introduce intermittent nips to a filament yarn so as to improve its performance in textile processing. The effect of various interlacing nozzle geometries on the interlacing process was studied. The geometries of interlacing nozzles with single or multiple air inlets located across the width of yarn channels are investigated. The basis case is the yarn channel, with a perpendicular main air inlet in the middle. Other cases have main air inlets, slightly inclined double sub air inlets, The yarn channel cross sectional shapes are either semicircular or rectangular shapes. The compressed impinging jet from the main air inlet hole hits the opposing bottom wall of the yarn channel, is divided into two branches, joins with the compressed air coming out from sub air inlet at the bottom and creates two free jets at both ends of the yarn channel. The compressed air movement in the cross-section consists of two opposing directional vortices. The CFD-FASTRAN flow parallel solver was used to perform steady simulations of impinging jet flow inside of the interlace nozzles. The vortical structure and the flow pattern such as pressure contour, particle traces, velocity vector plots inside of interlace nozzle geometry are discussed in this pater.