• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1487-1491
• /
• 2008

Detailed knowledge on the motion of blood cells flowing in micro-channels under simple shear flow and the influence of blood flow is essential to provide a better understanding on the blood rheological properties and blood cell aggregation. The microscopic behavior of red blood cell (RBCs) is numerically investigated using a fluid-structure interaction (FSI) method based on the Arbitrary-Lagrangian-Eulerian (ALE) approach and the dynamic mesh method (smoothing and remeshing) in FLUENT (ANSYS Inc., USA). The employed FSI method could be applied to the motions and deformations of a single blood cell and multiple blood cells, and the primary thrombogenesis caused by platelet aggregation. It is expected that, combined with a sophisticated large-scale computational technique, the simulation method will be useful for understanding the overall properties of blood flow from blood cellular level (microscopic) to the resulting rheological properties of blood as a mass (macroscopic).

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

• 한국자동차공학회논문집
• /
• 제6권4호
• /
• pp.101-107
• /
• 1998

A three-dimensional multi-phase flow is simulated around a smooth tire. This simulation is conducted by solving Navier-Stokes equation with a k-$\varepsilon$ turbulent model. The numerical calculations are carried out by modeling a multi-phase free surface flow mixed with air and water at the inlet. The numerical solutions show an intuitively resonable behavior of water around a moving tire. The calculated pressure around the tire surface along the moving direction is presented. The moving velocities of the tire are chosen to be 30, 40, 60, and 70 km/h. The numerically simulated pressures around the tire are compared with existing experimental data. The comparison shows a new possible tool of analyzing a hydroplaning phenomenon for an automobile tire by means of a computational fluid dynamics.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
• /
• pp.264-267
• /
• 2010

This research focuses on the development of numerical code to deal with compressible two phase flow around three dimensional objects combined with cavitation model suggested by Weishyy et al. with k-e turbulent model. The cryogenic cavitation is carried out by considering the thermodynamic effect on physical properties of cryogenic fluids in physical point of view and implementing the temperature sensitivity in the energy equation of the government equations in numerical point of view, respectively. The formulation has been extensively validated for both liquid nitrogen and liquid hydrogen by simulating the experiments of Hord on hydrofoils. Then, simulations of cavitating turbopump inducers at their design flow rate are presented. Results over a broad range of Nss numbers extending from single-phase flow conditions through the critical head break down point are discussed. In particular, thermal depression effects arising from cavitation in cryogenic fluids are identified and their impact on the suction performance of the inducer quantified.

• International Journal of Fluid Machinery and Systems
• /
• 제3권1호
• /
• pp.80-90
• /
• 2010

The cavity oscillation with swirling flow in hydraulic power generating systems was studied by a simple experiment and numerical simulation. Several types of fluctuation were observed in the experiment, including the cavitation surge caused by the diffuser effect and the vortex precession by the swirling flow. Both cavitation surge and vortex precession were simulated by CFD. Detailed flow structure was examined through flow visualization and CFD.

• 한국자동차공학회논문집
• /
• 제6권6호
• /
• pp.15-23
• /
• 1998

A three dimensional simulation of the fluid flow in an automotive torque converter was conducted adopting the mixing plane model implemented in the computational fluid dynamics program CFD-ACE. The present numerical results for performance characteristics showed a good agreement with the experimental results. In the flow of the torque converter, recirculating flow regimes were found mostly at the suction side of each element, which caused the performance decrease. The recirculating flow can be minimized by the optimization of the blade geometries.

• 대한교통학회지
• /
• 제27권1호
• /
• pp.27-34
• /
• 2009

도로교통망의 시스템변화에 대한 효과분석의 일환으로 1979년 Herman이 제시한 Two-Fluid Model을 적용하여 거시적인 교통류 변화특성을 분석하였으며, 이를 통해 도로시설의 운영개선 효과를 정량적으로 확인하였다. 본 연구에서는 일반국도 3호선 의정부 전체 구간의 약 8km, 총 31개 신호교차로를 분석 대상으로 하며, TSIS CORSIM 및 Run Time Extension을 이용한 미시적 시뮬레이션 분석으로 현황 및 개선 대안에 대한 개별차량의 주행정보를 추출하였다. Two-Fluid Model의 파라메타 산출결과 현황 대비 신호제어시스템 개선 시 네트워크의 서비스 질을 의미하는 단위거리 당 평균최소통행시간(Tm)은 약 35% 감소하였으며, 네트워크 수요증가에 대한 저항성을 의미하는 파라메타 n은 약 28%의 향상된 결과를 나타내었다. 국도 축을 대상으로 하는 시뮬레이션 기반의 자료 수집으로 인해 제한된 연구결과이나 Two-Fluid Model이 신호 최적화 및 연동형 반감응제어의 적용 등 신호제어시스템 개선에 대한 우수한 거시적 효과평가 지표로 활용되어 질 수 있음을 확인하였다.

• International Journal of Fluid Machinery and Systems
• /
• 제2권4호
• /
• pp.346-352
• /
• 2009

The objective of the present work is to improve numerical predictions of unsteady turbulent swirling flows in the draft tubes of hydraulic power plants. We present Large Eddy Simulation (LES) results on a simplified draft tube consisting of a straight conical diffuser. The basis of LES is to solve the large scales of motion, which contain most of the energy, while the small scales are modeled. LES strategy is here preferred to the average equations strategies (RANS models) because it resolves directly the most energetic part of the turbulent flow. LES is now recognized as a powerful tool to simulate real applications in several engineering fields which are more and more frequently found. However, the cost of large-eddy simulations of wall bounded flows is still expensive. Bypass methods are investigated to perform high-Reynolds-number LES at a reasonable cost. In this study, computations at a Reynolds number about 2 $10^5$ are presented. This study presents the result of a new near-wall model for turbulent boundary layer taking into account the streamwise pressure gradient (adverse or favorable). Validations are made based on simple channel flow, without any pressure gradient and on the data base ERCOFTAC. The experiments carried out by Clausen et al. [1] reproduce the essential features of the complex flow and are used to develop and test closure models for such flows.

• 한국게임학회 논문지
• /
• 제14권3호
• /
• pp.55-62
• /
• 2014

파티클 기반의 유체 시뮬레이션에서 파티클 들이 경계면에 부딪쳐 쇄파를 일으키는 경우 과도한 움직임으로 인해 자연스러운 흐름을 표현하기 어렵다. 파티클이 이동하는 시간 간격을 세분화하여 선형보간 함으로써 이 문제를 해결할 수 있다. 이렇게 하면 경계면에 모여 압력이 높아진 파티클 들의 가속도 벡터가 부드럽게 변한다. 하지만 보간을 하기위한 최소 샘플수가 높기 때문에 파티클 들이 점성을 가진 액체처럼 뭉치는 문제가 발생한다. 본 연구에서는 이 문제를 해결하기 가중치 보간 방식을 사용한다. 가중치 보간은 파티클의 현재 가속벡터와 이전 가속벡터에 서로 다른 가중치를 주며 차례로 더해 이동벡터를 구한다. 가중치 보간 방식을 쓰면 비슷한 흐름을 표현하는데 필요한 샘플수가 선형 보간 방식보다 적다. 그 결과로 점성을 가진 액체처럼 뭉치는 선형보간 방식의 문제점을 해결할 수 있다.

• 한국안전학회지
• /
• 제35권3호
• /
• pp.96-104
• /
• 2020

The numerical simulations were conducted to investigate the thermal-fluid phenomena occurred inside the experimental apparatus during a PCCS, used to remove heat released in accidents from a containment of light water nuclear power plant, operation. Numerical simulations of the flow and heat transfer caused by wall condensation inside the containment simulation vessel (CSV), which equipped with 18 vertical heat exchanger tubes, were conducted using the commercial computational fluid dynamics (CFD) software ANSYS-CFX. Shear stress transport (SST) and the wall condensation model were used for turbulence closure and wall condensation, respectively. The simulation using the actual size of the apparatus. However, rather than simulating the whole experimental apparatus in consideration of the experimental cases, calculation resources, and calculation time, the simulation model was prepared only in CSV. Selective simulation was conducted to verify the effects of non-condensable gas(NC gas) concentration, CSV internal pressure, and wall sub-cooling conditions. First, as a result of the internal flow of CSV, it was observed that downward flow due to condensation occurred surface of the vertical tube and upward flow occurred in the distant place. Natural convection occurred actively around the heat exchanger tube. Due to this rising and falling internal flow, natural circulation occurred actively around the heat exchanger tubes. Next, in order to check the performance of built-in condensation model using according to the non-condensable gas concentration, CSV internal flow and wall sub-cooling, the heat flux values were compared with the experimental results. On average, the results were underestimated with and error of about 25%. In addition, the influence of CSV internal pressure and wall sub-cooling was small, but when the condensate was highly generated due to the low non-condensable gas concentration, the error was large compared to the experimental values. This is considered to be due to the nature of the condensation model of the CFX code. However, in spite of the limitations of CFD, it is valid to use the built-in condensation model of CFD for PCCS performance prediction from a conservative perspective.