• 국제초고층학회논문집
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• 제1권2호
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• pp.87-97
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• 2012

The indoor environments in high-rise buildings are generally well enclosed by defined boundary conditions. Here, a numerical simulation method based on the Lattice Boltzmann method (LBM), which aims to model and simulate the turbulent flow accurately in an enclosed environment, and its comparison with traditional computational fluid dynamics (CFD) results, are presented in this paper. CFD has become a powerful tool for predicting and evaluating enclosed airflows with the rapid advance in computer capacity and speed, and various types of CFD turbulence modeling and its application and validation have been reported. The LBM is a relatively new method; it involves solving of the discrete Boltzmann equation to simulate the fluid flow with a collision model instead of solving Navier-Stokes equations. In this study, the LBM-based scheme of flow pattern and particle dispersion analyses are validated using the benchmark test case of two- and three-dimensional and isothermal conditions (IEA/Annex 20 case); the prediction accuracy and advantages are also discussed by comparison with the results of CFD.

• 수산해양기술연구
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• 제53권4호
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• pp.446-455
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• 2017

The improvement of resistance performance for the 4.99 ton class fishing boats was shown. The 4.99 ton fishing boats are the most commonly used one in the Korean coastal region. The evaluation of resistance performance was estimated by the Computational Fluid Dynamics (CFD) analysis. The CFD simulation was performed by the validation for various types of bow shapes on the hull. The optimized hull form from the simulation was selected and showed the best resistance performance. This hull type was tested on the towing tank in the National Institute of Fisheries Science (NIFS). The effective horsepower (EHP) was estimated by the resistance test on the towing tank with the bare hull condition. The drag force on the three service speed conditions was obtained for the resistance analysis to power prediction. The measured drag forces are compared with the results from the CFD simulation with one another. As results of the model tests, it was confirmed that the shape of the bow is an important factor in the resistance performance. The effective horsepower decreased about 30% in comparison with the conventional hull form. Also, the resistance performance improved the reduction of required horsepower, which especially contributed to the energy-saving for the fisheries industry. In the CFD analysis, the resistance performance improved slightly. In this case, the ratio of the residual resistance ($C_R$) in the total resistance ($C_T$) was high. Therefore, the CFD analysis was not enough to satisfy with reflection for the free surface and wave form in the CFD procedure. Both model test and CFD calculation in this study can be applied to the initial design process for the coastal fishing vessel.

• 한국태양에너지학회 논문집
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• 제26권3호
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• pp.99-110
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• 2006

This study focused on the emission rate of the construction materials. The method of study is as follows. First, validation of small chamber method to determine emission rate of construction material was performed by CFD simulation. For the result of this study, uniform air velocity in small chamber was founded, and small chamber as a test material for emission rate was validated. Second, the construction materials were categorized by their feature and the emission rate of volatile organic compound was determined. Totally, VOCs emission rate of 49 materials were determined.

• 한국전산유체공학회지
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• 제21권2호
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• pp.62-69
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• 2016

It has been highly demanded to improve the accuracy of CFD(Computational Fluid Dynamics) methods for the assessment of the hydrodynamic performance of marine propellers in cavitating and non-cavitating flows. This paper presents a validation study on the numerical simulation of the tip vortex flow of a non-cavitating marine propeller SVA VP1304. The calculations are carried out by using the Reynolds averaged Navier-Stokes(RANS) approach, where the Reynolds Stress Model(RSM) is used for turbulence closure. The present paper contains a grid dependence test for the propeller open water simulations and a special emphasis is placed on conducting a local grid adaptation on the blade tip and in the tip vortex to reasonably reproduce the velocity and the pressure in the tip vortex flow field. The numerical results are compared with the experimental validation data, which are published in the second International Symposium on Marine Propulsors 2011(SMP'11). The present numerical results show a reasonable agreement with the experiments.

• Wind and Structures
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• 제22권4호
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• pp.503-524
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• 2016

The suitability of Computational Fluid Dynamics (CFD) simulations on the built environment for the purpose of estimating average roughness characteristics and for studying wind flow patterns within the environment is assessed. Urban models of various levels of complexity are considered including an empty domain, array of obstacles arranged in regular and staggered manners, in-homogeneous roughness with multiple patches, a semi-idealized built environment, and finally a real built environment. For each of the test cases, we conducted CFD simulations using RANS turbulence closure and validated the results against appropriate methods: existing empirical formulas for the homogeneous roughness case, empirical wind speed models for the in-homogeneous roughness case, and wind tunnel tests for the semi-idealized built environment case. In general, results obtained from the CFD simulations show good agreement with the corresponding validation methods, thereby, giving further evidence to the suitability of CFD simulations for built environment studies consisting of wide-ranging roughness. This work also provides a comprehensive overview of roughness modeling in CFD-from the simplest approach of modeling roughness implicitly through wall functions to the most elaborate approach of modeling roughness explicitly for the sake of accurate wind flow simulations within the built environment.

• 한국항공우주학회지
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• 제45권3호
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• pp.217-225
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• 2017

본 연구는 국내 외 풍동기관들의 정적 공력측정 결과의 상호 비교검증 및 EFD-CFD 검증을 위해 수행되었다. 공군사관학교에서는 NRC 모델 기반 표준 동안정 모델을 제작하여 정적 특성을 측정하고, 풍동시험의 정확성 검증을 위하여 한국항공우주연구원 및 NRC에서 측정된 정적 공력측정 데이터를 상호 비교하였다. 또한 풍동시험 결과를 전산해석 결과와 비교하였으며 전산해석 유동장에서 분석된 오차원인을 확인하기 위하여 스트레이크 영향성을 검토하였다. 그 결과, EFD-CFD 간 피칭모멘트의 경향성이 상이하였으며, 스트레이크 효과는 크게 나타나지 않았다. 따라서 후방 지지대, 표준 동안정 모델의 흡입구에서 발생하는 와류에 의한 오차 분석과 전산해석의 격자해상도 재구성 등의 추가연구 진행이 필요한 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제42권4호
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.14-16
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• 2007

A critical problem in the integration of stores into new and existing aircraft is the safe separation of the stores from the aircraft at a variety of flight conditions representative of the aircraft flight regime. Typically, the certification of a particular store/aircraft/flight condition combination is accomplished by a flight test. Flight tests are very expensive and do expose the pilot and aircraft to a certain amount of risk. Wind tunnel testing, although less expensive than flight testing, is still expensive. Computational Fluid Dynamics(CFD) has held out the promise of alleviating expensive and risk by simulating weapons separation computationally. The forces and moments on a store at carriage and at various points in the flow field of te aircraft can be computed using CFD applied to the full aircraft and store geometry. This study needs full dynamic characteristics study and flow analysis for securing store separation safety. Present study performs dynamic simulation of store separation with flow analysis using Chimera grid scheme which is usually used for moving simulations.

• 한국산업융합학회 논문집
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• 제25권1호
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• pp.55-60
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• 2022

This study conducted the measurements of air flow rate for blower systems with experiment and numerical. A new airflow rate test method is suggested, with which it is possible to accurate measurements and calculate the air flow rate for blower systems. The blower(axial fan) is an industrial fluid machine device that supplies a large amount of air by driving an impeller with an electric motor, and it is widely used throughout the industry such as steel, power plant, chemical, semiconductor, LC D, food, and cement. The airflow from the blower is for exchanging the heat in the cooling unit or heat exchanger. The temperature of coolants and hydraulic oil primarily depends on the amount of airflow rate through the cooling package so its accurate estimation is very important. Moreover, it required a larger investment in time and cost since it could not be executed until the system is actually made. Therefore, this research is intended to examine the phenomenon of air flow pattern when testing air flow rate, suggested new test method, and show the result of the validation test.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4382-4394
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• 2023

Passive auto-catalytic recombiners (PARs) are widely used to mitigate a hydrogen hazard. The first step to evaluate the hydrogen safety by PARs is to obtain qualified test data of the PARs for validation of their analytical model. SPARC PAR tests SP8 and SP9 were conducted to evaluate the hydrogen recombination characteristics of a honeycomb-shaped catalyst PAR. To obtain the hydrogen recombination rate from the PAR test data, two methods, Method-1 and Method-2, introduced by the THAI project, were applied. Since a large gradient of hydrogen concentration developed during hydrogen injection can cause a large error in the hydrogen mass obtained by integrating the measured hydrogen concentrations, a gate was installed at the PAR inlet to homogenize hydrogen in the test vessel before the PAR operation in the tests. A computational fluid dynamics (CFD) code with a PAR model was also applied to evaluate the characteristics of the PAR recombination according to the PAR inlet conditions, and the results were compared with those from Method-1 and Method-2. It was confirmed that the recombination rates from Method-1 require a correction factor to be compatible with results from Method-2 and the CFD simulation in the case of the SPARC-PAR tests.