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강형석(H.S. Kang),김연식(Y.S. Kim),전형길(H.G. Chun),송철화(C.H. Song) 한국전산유체공학회 2006 한국전산유체공학회지 Vol.11 No.2
A CFD benchmark calculation for a steam blowdown test was performed for 30 seconds to develop the methodology of numerical analysis for the thermal mixing between steam and subcooled water. In the CFD analysis, the grid model simulating the sparger and the IRWST pool were developed by the axisymmetric condition and then the steam condensation phenomena by a direct contact was modelled by the so-called condensation region model. Thermal mixing phenomenon in the subcooled water tank was treated as an incompressible flow, a free surface flow between the air and the water, a turbulent flow, and a buoyancy flow. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small temperature difference was locally found at some locations. The commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behavior reasonably well when a sufficient number of mesh distribution and a proper numerical method are adopted.
IRWST 환형관 실험장치 내의 수소화염 가속현상에 대한 CFD 해석 연구
강형석(H.S. Kang),하광순(K.S. Ha),김상백(S.B. Kim),홍성완(S.W. Hong) 한국전산유체공학회 2012 한국전산유체공학회지 Vol.17 No.3
We developed a preliminary CFD analysis methodology to predict a pressure build up due to hydrogen flame acceleration in the APR1400 IRWST on the basis of CFD analysis results for test data of hydrogen flame acceleration in a scaled-down test facility performed by Korea Atomic Energy Research Institute. We found out that ANSYS CFX-13 with a combustion model of the so-called turbulent flame closure and a model constant of A = 5.0, a grid model with a hexahedral cell length of 5.0 mm, and a time step size of 1.0 × 10<SUP>-5</SUP> s can be a useful tool to predict the pressure build up due to the hydrogen flame acceleration in the test results. Through the comparison of the simulated results with the test results, we found out that the proposed CFD analysis methodology enables us to predict the peak pressure within an error range of about ±29% for the hydrogen concentration of 19.5%. However, the error ranges of the peak pressure for the hydrogen concentration of 15.4% and 18.6% were about 66% and 51%, respectively. To reduce the error ranges in case of the hydrogen concentration of 15.4% and 18.6%, some uncertainties of the test conditions should be clarified. In addition, an investigation for a possibility of flame extinction in the test results should be performed.
가변 단면을 가지는 비대칭 얇은 관 부품의 액압 성형 연구
강형석(H. S. Kang),주병돈(B. D. Joo),이민(M. Li),황태우(T. W. Hwang),문영훈(Y. H. Moon) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
Hydroforming of non-axisymmetric thin-wall tubular component with variable cross sections was analyzed. In order to solve sealing problem occurred due to thin and non-axisymmetric shape, punch available on hydroforming experiment with thin tube was suggested. Lead patch was attached to the punch to solve sealing problem occurred due to the stress gradient on the non-axisymmetric shape. FEM and experiments have also been performed to analyze these sealing problems associated with the punch shape and non-axisymmetric shape. Finally, lead patch is attached at tube surface where intensive local strain concentration would occur to enhance hydroformability. These methods were successfully used to fabricate non-axisymmetric thin-wall tubular component with variable cross sections that had previously failed during traditional hydroforming processing.
Westinghouse 1/7 실험장치의 증기발생기 입구플레넘 내의 자연대류 유동에 대한 CFD 해석방법론 개발
강형석(H.S. Kang),김성일(S.I. Kim),하광순(K.S. Ha) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.3
Korea Atomic Energy Research Institute performed a CFD calculation of a natural convective flow in the steam generator inlet plenum at the Westinghouse 1/7 test facility to establish an analysis methodology for generating input parameters of the MELCOR code which will be used in analyzing the temperature induced steam generator tube rupture accident in an optimized power reactor 1000 MWe. Through this CFD analysis against the test results, we developed a CFD analysis methodology to accurately predict the recirculation ratio, thermal mixing fraction, and discharge coefficient with an error range of approximately ±10%. Though this CFD analysis methodology underestimated approximately 25% for the proposed hot tube number in the steam generator of the test results, we judged that this discrepancy may not be large when considering uncertainties resulted from 51 measured tube temperatures over all 216 tubes in the test facility. Finally, we found that the buoyancy turbulence generation plays an important role to control the natural convection flow in the steam generator inlet plenum because this model can enhance the recirculation flow. As a further work, we will apply the proposed CFD analysis methodology for other test cases conducted at the Westinghouse 1/7 test facility for producing various validation results.