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임계 노즐을 통하는 기체 유동의 유출계수와 임계 압력비에 관한 연구
김재형(J. H. Kim),우선훈(S. H. Woo),김희동(H. D. Kim),박경암(K. A. Park) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
The air flow through a critical nozzle with a small throat diameter is significantly affected by viscous<br/> effect. In this paper, computational study using the axisymmetric, compressible, Navier-Stokes Equations is<br/> carried out to analy ze flow characteristic through a critical nozzle at low-Reynolds numbers. The nozzle<br/> throat diameters of D=0.28~4.48mm are used in this study. Computational results are compared with the<br/> previous experimented ones. It is found that the present computational results predict the critical pressure ratio<br/> and the discharge coefficient well. As the diameter of a critical nozzle increases, the discharge coefficient and<br/> critical pressure ratio increase. At the nozzle throat, the displacement and momentum thicknesses of the<br/> boundary layer are obtained by an empirical equation.
김환열(H. Y. Kim),박종화(J. H. Park),김희동(H. D. Kim),홍성완(S. W. Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
If a molten core is released from a reactor vessel into a reactor cavity during a severe accident, an important safety issue of coolability of the molten core from top-flooding and concrete ablation due to a molten core concrete interaction (MCCI) is still unresolved. The released molten core debris would attack the concrete wall and basemat of the reactor cavity, which will lead to inevitable concrete decompositions and possible radiological releases. In a OECD/MCCI project scheduled for 4 years from 2002. 1 to 2005. 12, a series of tests were performed to secure the data for cooling the molten core spread out at the reactor cavity and for the 2-D long-term core concrete interaction (CCI). The tests included not only separate effect tests such as a melt eruption, water ingression, and crust failure tests with a prototypic material but also 2-D CCI tests with a prototypic material under dry and flooded cavity conditions. The paper deals with the transient simulations on the CCI-2 test by using a severe accident analysis code CORQUENCH, which was developed at Argonne National Laboratory (ANL). Similar simulations had been already performed by using MELCOR 1.8.5 code. Unlike the MELCOR 1.8.5, the CORQUENCH includes a melt eruption model and a newly developed water ingression model based on the water ingression tests under the OECD/MCCI project. In order to adjust the geometrical differences between the CCI-2 test (rectangular geometry) and the simulations (cylindrical geometry), the same scaling methodology as used in the MELCOR simulation was applied. For the direct comparison of the simulation results, the same inputs for the MELCOR simulation were used. The simulation results were compared with the previous results by using MELCOR 1.8.5.
3-D CFD Investigation of the Compressible Flows through Pipe Bends
Abhilash Suryan,H. D. Kim(김희동) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Pipe bends are encountered in many compressible flow applications. The characteristics of compressible gas flow through pipe bends are not yet fully understood since the flow can choke at the bend, with possibly strong oscillations due to the secondary flow or separation. As a result, the mass flow rate through the pipe bend to vary with time, affecting the performance of whole flow system. In the present investigation the characteristics of compressible gas flow through pipe bends is studied by computational fluid dynamics method. Three dimensional, compressible Navier-Stokes equations are solved using a fully implicit finite volume scheme. The pressure ratio, downstream to upstream pressure, of the bend is varied to investigate the effects on the flow characteristics for two geometries of pipe bends. The results obtained are compared with experimental results.