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  • Title/Summary/Keyword: CFD 유동해석

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Numerical Modeling of Turbulent Open Channel Flow Downstream of a Drop Structure (하상단차 하류부 난류흐름 거동 수치모의)

  • Kim, Byung Joo;Paik, Joong Cheol
    • Proceedings of the Korea Water Resources Association Conference
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    • 2021.06a
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    • pp.244-244
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    • 2021
  • 난류흐름 거동은 지형이나 수공구조물과 같은 고체 경계면의 변화에 민감하게 반응하며 특징 또한 다양하다. 보나 여수로 등과 같은 단차 구조물을 통과하는 흐름은 구조물의 모서리 같은 흐름 경계면이 급변하는 지점에서는 흐름분리(flow separation)가 발생하는 것이 특징이다. 이러한 흐름분리로 인해 전단층이 발생하며 흐름 재순환(recirculation)이 구조물 하류부에 형성된다. 이 연구에서는 낙차공 형식의 단차 구조물 하류부에서의 흐름 거동을 이해하기 위해 CFD모델링을 통하여 계산된 3차원 유동장을 분석한다. 난류 모의는 하이브리드 LES(large-eddy simulation)/RANS 계산 기법인 IDDES(improved delayed detached-eddy simulation)기법을 적용한다. IDDES의 기본 모형으로는 k-ω SST모형과 Spalart-Allmaras모형을 이용하여 두 모형의 성능을 평가한다. 자유수면의 변동은 VoF(volume of fluid)기법을 이용하여 계산하며, 각 지배방정식은 최소의 수치분산을 유지하면서 수치해의 안정성을 확보할 수 있는 2차 정확도의 유한체적법을 이용하여 이산화하였다. 수치해석 결과는 레이놀즈수 23,400과 후르드수 0.22의 조건에서 기존에 계측된 자료와 비교하여 수치모형의 정확도를 평가하고 하상 단차 하류부에서의 흐름 거동 특성을 분석한다. 계산 결과는 공학적으로 널리 사용되는 RANS 수치모의에서 볼 수 없는 전단층과 난류구조의 동적 거동 특성과 이에 따른 레이놀즈 응력분포의 특성을 설명해준다.

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Experimental and Numerical Study on Flow Characteristics of a Common Exhaust System for Multiple SOFCs (SOFC용 복합 배기 시스템 유동 특성에 관한 실험 및 수치해석적 연구)

  • DAEWOONG JUNG;JONGHYUK YOON;HYOUNGWOON SONG
    • Journal of Hydrogen and New Energy
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    • v.34 no.6
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    • pp.657-666
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    • 2023
  • In this study, experiments and numerical analysis were conducted to investigate the exhaust gas flow in a common exhaust system of multiple solid oxide fuel cells. The system was fabricated based on KGS code and operated within a pressure range of 0.12 kPa, with flow rates ranging from 79.1 to 103.4 L/min. Numerical modeling was validated with a mean absolute error of 3.8% for pressure results. The study assessed the impact of changes in area ratio and emergency stops on pressure distribution, velocity vectors, and wall shear stress. The findings revealed no significant factors causing high differential pressure or backflow.

Analysis of Flow Characteristics of Triple Filter System by the Influence of Filter Density (필터 조밀도의 영향에 의한 3단 필터 시스템의 유동특성 해석)

  • In-Soo Son
    • Journal of the Korean Society of Industry Convergence
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    • v.26 no.6_2
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    • pp.1163-1169
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    • 2023
  • In this study, the flow characteristics of the filter system were analyzed due to the effect of the density of the filter in the triple filter system. Flow analysis was performed as a flow passing through a porous medium. The flow characteristics of each filter system were analyzed by arranging filters with different densities in the forward flow flow and the reverse flow. The arrangement order of the triple filters was excellent in the case of forward fluid flow and in the case of higher density from the inside to the outside filter. In the reverse flow filter system, the performance of the system was the best in the case of reverse order filter arrangement. As a result of the analysis, Case II, which showed a pressure drop rate of 5.65% for forward flow, was the best in the reverse direction with a pressure drop rate of 14.25%. Considering reverse and forward flows, it was found that the optimal filter arrangement was most effective when the intermediate filter was the densest, and the inner or outer filter was less dense.

Numerical Study on the Reaction Force and Flow Characteristics of Firefighting Monitor Based on Decompression Equipment Designs (감압장치 형상에 따른 소방용 방수총의 반동력 및 유동 특성에 관한 전산해석 연구)

  • Sang Hwan Park;Kwanwoo Lee;Dong Kim;Murim Kim;Sang Hyun Park;Junyoung Lee;Kyoungsik Chang
    • Journal of the Korean Society of Visualization
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    • v.22 no.3
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    • pp.37-44
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    • 2024
  • The Firefighting Monitor is essential for large-scale firefighting, but the reaction force generated during high-pressure water discharge poses control challenges. In robotic control systems, reaction forces can reduce the precision of spraying operations. In this paper, we aim to determine the optimal design of decompression equipment to mitigate reaction forces in nozzles. Three configurations (None, Orifice, and Airfoil) were designed and evaluated using Computational Fluid Dynamics (CFD) simulations. The results demonstrated that the Airfoil shape exhibited the lowest upward reaction force and superior performance in terms of reaction force reduction under four inlet pressures and both at 0° and 45° conditions. The Airfoil shape was identified as the most effective in reducing reaction forces and improving flow stability.

Analysis on the Internal Flow of the Hydraulic Dual Chambers Applying Various Orifice (다양한 오리피스를 이용한 연결형 공압 챔버 내부 유동 해석)

  • Cho, Kihong;Park, Jungho;Kim, Euiyong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.18 no.1
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    • pp.58-64
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    • 2014
  • Hydraulic dual chamber, as the simulator for a dual pulse rocket motor, was tested by a high pressure device with various orifice-hole size being applied. Pressure difference occurs between 1st chamber and 2nd chamber depending on area ratio of the orifice to nozzle throat. Studying a design configuration of the orifice is essential to the motor development because pressure difference severely affects the rocket motor performance. It is noticed in this study that energy dissipation is caused by the vortex flow originating from the orifice as the 2nd chamber is operated. The flow field is simulated by a commercial computational fluid dynamics program, ANSYS FLUENT V14.5.

Numerical Analysis of Non-Cavitating and Cavitating Performance of a SVA Potsdam Propeller (SVA Potsdam 프로펠러 단독 및 캐비테이션 성능 수치해석)

  • Kim, Je-In;Park, Il-Ryong;Kim, Ki-Sup;Ahn, Jong-Woo
    • Journal of the Society of Naval Architects of Korea
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    • v.54 no.3
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    • pp.215-226
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    • 2017
  • This paper presents numerical results of the performance of a marin propeller in cavitating and non-cavitating flow conditions. The geometry and experimental validation data of the propeller are provided in Potsdam Propeller Test Case(PPTC) in the framework of the second International Symposium on Marine Propulsors 2011(SMP'11) workshop. The PPTC includes open water tests, velocity field measurements and cavitation tests. The present numerical analysis was carried out by using the Reynolds averaged Navier-Stokes(RANS) method on a wall-resolved grid ensuring a y+=1, where the SST k-ω model was mainly used for turbulence closure. The influence of the turbulence model was investigated in the prediction of the wake field under a non-cavitating flow condition. The propeller tip vortex flows in both cavitating and non-cavitating conditions were captured through adaptation of additional grids. For the cavitation flows at three operation points, Schnerr-Sauer's cavitation model was used with a Volume-Of Fluid(VOF) approach to capture the two-phase flows. The present numerical results for the propeller wake and cavitation predictions including the open water performance showed a qualitatively reasonable agreement with the model test results.

Upgrade Development of a Centrifugal Compressor for Marine Engine Turbochargers (선박용 터보차져 원심압축기의 성능향상 개발)

  • Oh, Jong Sik;Oh, Koon Sup;Yoo, Kwang Taek
    • The KSFM Journal of Fluid Machinery
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    • v.3 no.1 s.6
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    • pp.43-50
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    • 2000
  • Upgrade development of a high pressure ratio centrifugal compressor in marine engine turbochargers is presented. A new matched operating point at increased speed of rotation was determined through system cycle analysis using the exisitng test data of turbine performance. Under some severe restrictions for geometric parameters, the state-of-the-art methods of both aerodynamic design and CFD analysis were applied, in which only an impeller, a vaned diffusor and some part of casing wall were modified. Prototype hardware was fabricated and assembled for system performance tests. Excellent performance in pressure ratio and efficiency was obtained over whole speed region. Reduced surge and choke margin was, however, observed at design speed of rotation.

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Study on Installed Performance Simulation of Aircraft Gas-Turbine Engine Considering Inlet and Exhaust Losses (흡배기구 손실예측 및 이를 고려한 항공기 가스터빈의 장착 성능모사 연구)

  • Kong, Chang-Duk;Owino, George.Omollo.
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.4
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    • pp.100-108
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    • 2006
  • Experimental study has been a general way to evaluate inlet and exhaust duct performances, but this is not only costly but also time consuming. Computational simulation is hence replacing experimental study and consequently time and cost saving. This paper therefore aims to investigate typical component performance of the intake and exhaust ducts using 3D representation. In this study a specific inlet and exhaust was modeled and analyzed to estimate its losses and flow field using computational fluid dynamic program with flow visualization capabilities. A process that requires geometry data to be modeled. That allowed for possibility of design trade off in designing phase. Installed performance of a specific turbo shaft engine was finally evaluated with the estimated inlet, exhaust and other accessories losses.

The Passenger Evacuation Simulation Using Fluent and EXODUS (Fluent와 EXODUS를 이용한 승객피난 시뮬레이션)

  • Jang, Yong-Jun;Lee, Chang-Hyun;Park, Won-Hee;Jung, Woo-Sung
    • Journal of the Korean Society for Railway
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    • v.11 no.1
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    • pp.95-100
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    • 2008
  • The simulation analysis of fire-driven flow and passenger evacuation in Daegu subway station, Chung-Ang, have been performed. The first location of outbreak of fire is inside passenger car in the third basement in Chung-Aug station, The smoke flow in the second and third basement has been analyzed using FLUENT 6.2. The CO (carbon monoxide) and temperature distribution in the train units and station platform have been obtained and transferred to input data for evacuation simulation. The highest temperature in the train units was 1500k. For the simulation of passenger evacuation, EXODUS has been used for whole basements (level 1level 3) in the station. Total number of people was assumed to be one thousand and 640 were placed inside train and 360 were placed outside train. In evacuation simulation, an average of 135 passengers were killed and an average time to evacuate takes 10min 19sec. The main evacuation routes used by passengers were investigated and the cause of death was identified by evacuation simulation.

Numerical Study of Fluidic Device in APR1400 Using Free-Surface Model (자유수면모델을 활용한 APR1400 유량조절장치의 수치해석 연구)

  • Lim, Sang-Gyu;You, Sung-Chang;Kim, Han-Gon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.7
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    • pp.767-774
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    • 2012
  • A fluidic device (FD) has been adopted in the safety injection tanks (SITs) of APR1400. A flow control mechanism of the FD was used to vary the flow regime in the vortex chamber corresponding to the SITs water level. The flow regime in the vortex chamber has a different pressure loss from low to high in accordance with the SITs water level. Nitrogen at the top of the SIT could be released owing to inertia of discharge flow when changing from a high flow rate to a low flow rate. This phenomenon is important to design improvement perspective because it can affect the performance of the FD. This paper shows a result of a preliminary numerical study to obtain the transient data related to air release in the flow turn-down period using a two-fluid free-surface model provided from ANSYS CFX 13.0. In conclusion, there is no significant effect on the performance of the FD, though a small quantity of air is released during the flow turn-down period.