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예조건화 HLLC 기법을 이용한 저 마하수 축소-확대 노즐의 준 1차원 이상유동 해석
염금수(G.S. Yeom) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.1
In this paper, quasi-one-dimensional two-phase flows through converging-diverging nozzles are simulated using a preconditioned HLLC method applied to a compressible two-pressure, one-velocity two-phase flow model. An efficient method estimating a reference Mach number used in the preconditioned scheme has been newly proposed. The developed code has been validated by the benchmark problems of a single-phase liquid water flow and a two-phase water-air flow through a linear nozzle. The computed results are good agreement with the previous one. It is noted that the present computations for the volume fraction profile show somewhat more accurate results than the previous one. The developed code can be used for solving the cavitation problem in water flows through nozzles and hydrofoils.
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.
다양한 액체에 떠 있는 부피가 일정한 버블의 형상 비교
염금수(G.S. Yeom) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.2
In this study, an accurate numerical method has been implemented to compute the shape of floating bubbles. Using the developed code, we have compared and analyzed how the shape of bubbles with a constant volume is changed when floating on six different liquids. Except when the volume of the bubble is very small or large, it has been confirmed that the shape and the rising height from the free surface were significantly changed according to liquids or capillary lengths. In addition, it has been found that the smaller the capillary length, the higher the bubbles were floating on. Since the shape of the isovolumetric bubble differs considerably depending on the liquid, the bursting of the bubble is expected to change accordingly.
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.