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문현기,Yoon Sujong,Tano-Retamale Mauricio,Epiney Aaron,송민섭,정재호 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.10
A high-fidelity computational fluid dynamics (CFD) analysis was performed using the Large Eddy Simulation (LES) model for the lower plenum of the HigheTemperature Test Facility (HTTF), a ¼ scale test facility of the modular high temperature gas-cooled reactor (MHTGR) managed by Oregon State University. In most nextegeneration nuclear reactors, thermal stress due to thermal striping is one of the risks to be curiously considered. This is also true for HTGRs, especially since the exhaust helium gas temperature is high. In order to evaluate these risks and performance, organizations in the United States led by the OECD NEA are conducting a thermal hydraulic code benchmark for HTGR, and the test facility used for this benchmark is HTTF. HTTF can perform experiments in both normal and accident situations and provide high-quality experimental data. However, it is difficult to provide sufficient data for benchmarking through experiments, and there is a problem with the reliability of CFD analysis results based on Reynoldseaveraged NaviereStokes to analyze thermal hydraulic behavior without verification. To solve this problem, high-fidelity 3-D CFD analysis was performed using the LES model for HTTF. It was also verified that the LES model can properly simulate this jet mixing phenomenon via a unit cell test that provides experimental information. As a result of CFD analysis, the lower the dependency of the subgrid scale model, the closer to the actual analysis result. In the case of unit cell test CFD analysis and HTTF CFD analysis, the volume-averaged sub-grid scale model dependency was calculated to be 13.0% and 9.16%, respectively. As a result of HTTF analysis, quantitative data of the fluid inside the HTTF lower plenum was provided in this paper. As a result of qualitative analysis, the temperature was highest at the center of the lower plenum, while the temperature fluctuation was highest near the edge of the lower plenum wall. The power spectral density of temperature was analyzed via fast Fourier transform (FFT) for specific points on the center and side of the lower plenum. FFT results did not reveal specific frequencydominant temperature fluctuations in the center part. It was confirmed that the temperature power spectral density (PSD) at the top increased from the center to the wake. The vortex was visualized using the well-known scalar Q-criterion, and as a result, the closer to the outlet duct, the greater the influence of the mainstream, so that the inflow jet vortex was dissipated and mixed at the top of the lower plenum. Additionally, FFT analysis was performed on the support structure near the corner of the lower plenum with large temperature fluctuations, and as a result, it was confirmed that the temperature fluctuation of the flow did not have a significant effect near the corner wall. In addition, the vortices generated from the lower plenum to the outlet duct were identified in this paper. It is considered that the quantitative and qualitative results presented in this paper will serve as reference data for the benchmark.
CFD를 활용한 MW급 풍력발전기 블레이드 와류 발생기 형상 최적화 및 공력 특성 분석
문현기,박선호,하광태,정재호 한국풍력에너지학회 2021 풍력에너지저널 Vol.12 No.2
The aerodynamic characteristics of a vortex generator (VG) on a multi-MW wind turbine blade was investigated by computational fluid dynamics (CFD). VGs are essentially small fins that are installed toward the root of the wind turbine blade to reduce airflow separation. Separation flow on the wind turbine blade suction surface was captured by a Reynolds-averaged Navier-Stokes (RANS) steady flow simulation using a general-purpose code, ANSYS CFX. The numerical analysis methodology was verified by comparing the blade aerodynamic analysis results through CFD with blade element momentum theory (BEMT)-based program GH-Bladed results. An aerodynamic sensitivity study of the VG according to the design parameters of the VG was performed. Optimization was carried out by targeting parameters with low eddy current dissipation rates. According to the simulation, the VG reduces separation in the wind turbine blade root region. Furthermore, it was found that the aerodynamic coefficient of the wind turbine with VG installation increases up to 2.80% at the rated power.
문현기,박소현,김응수,정재호 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.1
In-vessel retention through external reactor vessel cooling (IVR-ERVC) is a severe accident management (SAM) strategy that has been adopted and used in many nuclear reactors such as AP1000, APR1400, and light water reactor etc. Some reactor accidents have raised concerns about nuclear reactors among residents, leading to a decrease in residents’ acceptability and many studies on SAM are being conducted. Experiments on IVR-ERVC are almost impossible due to its specificity, so fluid characteristics are analyzed through BALI experiments with similar condition. In this study, computational fluid dynamics (CFD) via Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) for BALI experiments were performed. Steady-state CFD analysis was performed on three turbulence models, and SST k-ω model was in good agreement with the experimental measurement temperature within the maximum error range of 1.9%. LES CFD analysis was performed based on the RANS analysis results and it was confirmed that the temperature and wall heat flux for depth was consistent within an error range of 1.0% with BALI experiment. The LES CFD analysis results were compared with those of the Lagrangian-based solver. LES matched the temperature distribution better than SOPHIA, but SOPHIA calculated the position of boundary between stratified layer and convective layer more accurately. On the other hand, Lagrangian-based solver predicted several small eddy behaviors of the convective layer and LES predicted large vortex behavior. The vibration characteristics near the cooling part of the BALI experimental device were confirmed through Fast Fourier Transform (FFT) investigation. It was found that the power spectral density for pressure at least 10 times higher near the side cooling than near the top cooling.
풍력발전기 나셀 내부 전장 시스템 하네스 모듈 대상 열적 민감도 분석
문현기,유병진,정재호 한국풍력에너지학회 2021 풍력에너지저널 Vol.12 No.3
In this study, thermal sensitivity analysis of the harness module in a wind turbine nacelle was performed through computational fluid dynamics (CFD) using a general-purpose code, ANSYS CFX, based on experimental results. Reynolds-averaged Navier-stokes (RANS) steady flow mulation results for a total of five cases and the experimental results were consistent within an error of 2.24% at the peak temperature increment. A thermal sensitivity study of the Reynolds number of the harness system operating at a low Reynolds number was performed. It was confirmed that the peak temperature increment is linearly related to the inverse of the Nusselt number. Reynolds number correlations for peak temperature and Nusselt number at low Reynolds number are presented. A thermal sensitivity study of the harness module according to the resistance of the circuit was performed, and the peak temperature was reduced by 8.3%. It is expected that decreasing the peak temperature of the harness module by optimization of circuit resistance significantly reduces the probability of fire in a wind turbine nacelle.