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Second Order Model for Free Surface Convection
김성오(Seong-O Kim) 한국전산유체공학회 1997 한국전산유체공학회지 Vol.2 No.2
VOF 방법에 의한 자유표면 유동계산의 정확성을 개선하기 위해 이차정도 모델을 개발하였다. 개발된 이차원 모델의 정확성을 비교하기 위하여 여러 가지 크기의 원형 및 Solitary wave 형상의 자유표면 유동을 통하여 기존에 개발된 두 가지의 일차정도 모델과 비교하였다. 비교결과 반경이 큰 원과 같이 곡률이 작은 형상의 경우에는 일차정도 모델도 비교적 정확한 결과를 보여주고 있으나 작은 반정의 원형이나 Solitary wave 와 같이 곡률이 큰 형상의 경우 일차정도 모델은 많은 오차를 보여주는 반면에 이차정도 모델은 어느 경우에나 매우 정확한 결과를 보여준다.
Second Order Model for Free Surface Convection
김성오(Seong-O Kim) 한국전산유체공학회 1997 한국전산유체공학회지 Vol.2 No.2
VOF 방법에 의한 자유표면 유동계산의 정확성을 개선하기 위해 이차정도 모델을 개발하였다. 개발된 이차원 모델의 정확성을 비교하기 위하여 여러 가지 크기의 원형 및 Solitary wave 형상의 자유표면 유동을 통하여 기존에 개발된 두 가지의 일차정도 모델과 비교하였다. 비교결과 반경이 큰 원과 같이 곡률이 작은 형상의 경우에는 일차정도 모델도 비교적 정확한 결과를 보여주고 있으나 작은 반정의 원형이나 Solitary wave 와 같이 곡률이 큰 형상의 경우 일차정도 모델은 많은 오차를 보여주는 반면에 이차정도 모델은 어느 경우에나 매우 정확한 결과를 보여준다.
김성오(Seong-O Kim),어재혁(Jae-Hyuk Eoh),최훈기(Hoon-Ki Choi) 한국전산유체공학회 2002 한국전산유체공학회지 Vol.7 No.3
An analytic methodology was developed for free surface motions between liquid metal coolant and cover gas in order to calculate the phenomena of gas entrainment in hot pool surface through IHX EMF and reactor core. The methodology was setup by applying the first order VOF convection model to CFX4 general purpose fluid dynamics analysis code. The methodology was validated by applying it to an experimental apparatus designed for free surface motions of KALIMER reactor. The distributions of free surface calculated by the present methodology were almost coincident with the experimental data. The developed methodology was applied to the KALIMER reactor of full power operating condition. The shapes of the free surface were nearly uniform. From the results, it was found that the altitude of the free surface from the IHX inlet nozzle of KALIMER reactor is high enough not to affect to free surface motions of generating gas bubbles from the turbulent shear flows such as hydraulic jump and water falls.
Second Order method for Free Surface Convectiona
김성오(Seong-O. Kim) 한국전산유체공학회 1997 한국전산유체공학회 학술대회논문집 Vol.1997 No.-
To improve the numerical analysis of free surface convection and its reconstruction, a second-order algorithm was developed based on the volume of fraction method. The second-order method is compared with the first-order methods through the simulation of the convection for various sizes circles and solitary waves. For the small curvature of a free surface, e. g. circles with a large diameter, the first order method such as the FLAIR's and the centered slope method, show relatively good predictions. However, for large curvature configurations, the first order methods show large distortion of free surface. On the contrary, the second-order model always shows powerful prediction capabilities of free surface convection.
이차모멘트 난류모델을 사용한 Rayleigh-Benard 자연대류 유동 해석
최석기(Seok-Ki Choi),김성오(Seong-O Kim) 한국전산유체공학회 2008 한국전산유체공학회 학술대회논문집 Vol.2008 No.-
This paper reports briefly on the computational results of a turbulent Rayleigh-Benard convection with the elliptic-blending second-moment closure (EBM). The primary emphasis of the study is placed on an investigation of accuracy and numerical stability of the elliptic-blending second-moment closure for the turbulent Rayleigh-Benard convection. The turbulent heat fluxes in this study are treated by the algebraic flux model with the temperature variance and molecular dissipation rate of turbulent heat flux. The model is applied to the prediction of the turbulent Rayleigh-Benard convection for Rayleigh numbers ranging from Ra=2×10? to Ra=10?, and the computed results are compared with the previous experimental correlations, T-RANS and LES results. The predicted cell-averaged Nusselt number follows the correlation by Peng et al.(2006) (Nu=0.162Ra<SUP>0.286</SUP>) in the ‘soft’ convective turbulence region (2×10?≤Ra≤4×10?) and it follows the experimental correlation by Niemela et al. (2000) (Nu=0.124Ra<SUP>0.309</SUP>) in the ‘hard’ convective tubulence region (10?≤Ra≤10?) within 5% accuracy. This results show that the elliptic-blending second-moment closure with an algebraic flux model predicts very accurately the Rayleigh Benard convection.
Lattice Boltzmann 방법을 사용한 자연대류 해석에서 열모델의 선택에 관한 연구
최석기(Seok-Ki Choi),김성오(Seong-O Kim) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.4
A comparative analysis of thermal models in the lattice Boltzmann method(LBM) for the simulation of laminar natural convection in a square cavity is presented. A HYBRID method, in which the thermal equation is solved by the Navier-Stokes equation method while the mass and momentum conservation are resolved by the lattice Boltzmann method, is introduced and its merits are explained. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with a deferred correction method to ensure stability of the solutions. The HYBRID method and the double ?population method are applied to the simulation of natural convection in a square cavity and the predicted results are compared with the benchmark solutions given in the literatures. The predicted results are also compared with those by the conventional Navier-Stokes equation method. In general, the present HYBRID method is as accurate as the Navier-Stokes equation method and the double-population method. The HYBRID method shows better convergence and stability than the double-population method. These observations indicate that this HYBRID method is an efficient and economic method for the simulation of incompressible fluid flow and heat transfer problem with the LBM.