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염금수 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.10
Underwater explosions are very complicated problem possessing many challenges for numerical modeling. In the present paper, a twodimensionalunderwater explosion near a free surface and a structural object is numerically investigated using a 6-equation diffuseinterfacemodel that is solved by a HLLC-type scheme with MUSCL-Hancock method based on the least-squares reconstruction andBarth and Jespersen’s limiter on quadrilateral unstructured grid. A long-time computation is performed to capture the important physicsof the underwater explosion: initial underwater shock propagation and its interaction with material interfaces, expansion and contractionof the explosive gas bubble, and water jetting near a structure on the collapse of the gas bubble. These phenomena are clearly observedby the appropriate flow visualization of the computed results.
계면마찰항을 고려한 이상유동에서 파동전파에 대한 수치적 연구
염금수(G.S. Yeom),장근식(K.S. Chang),정문선(M.S. Chung) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.11
We numerically investigated propagation of various waves in the two-phase .flows such as sound wave, shock wave, rarefaction wave, and contact discontinuity in terms of pressure, void Faction, velocity and density of the two phases. The waves have been generated by a hydrodynamic shock tube, a pair of symmetric impulsive expansion, impulsive pressure and impulsive void waves. The six compressible two-fluid two-phase conservation laws with interfacial Fiction terms have been solved in two Factional steps. The first PDE Operator is solved by the HLL scheme and the second Source Operator by the semi-implicit stiff ODE solver. In the HLL scheme, the fastest wave speeds were estimated by the analytic eigenvalues of an approximate Jacobian matrix. We have discussed how the interfacial friction terms affect the wave structures in the numerical solution.
염금수(Geum-Su Yeom),장근식(Keun-Shik Chang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
We investigate two-phase shock tube problems using the two-component two-phase flow formulations. In these problems, discontinuities are initially introduced in the properties of two-phase flow by a diaphragm located at the middle of the shock tube. Since the governing equations are of non-conservative form and the system eigenvalues are complex, numerical method is unstable. To tackle with the numerical instability, we introduce the interfacial pressure term in the momentum equations and employ HLL Riemann solvers that make use of the eigenvalues from an approximate Jacobian matrix. The present approach produced wave structures that agree well with the experiment and earlier computational results.
액적이 있는 비점성 공기유동 모델을 이용한 구름속의 천음속 에어포일 수치해석
염금수(G.S. Yeom),장근식(K.S. Chang),백승욱(S.W. Baek) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.5
In this paper, the problem of transonic aerodynamic characteristics of a NACA0012 airfoil is numerically investigated in the inviscid gas-droplet two-phase flow with the compressible two-fluid model. In the present study, the airfoil flight in the cloud is simulated by taking account of the viscous drag of the droplets, the heat transfer, the phase change, and the droplet fragmentation. The two-fluid equation system is solved by the fractional-step method and the WAF-HLL scheme. The effects of size and volume fraction of the droplets on the flow characteristics of the airfoil in the cloud are elaborated and discussed.