• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.193-200
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• 2009

Recently, there have been efforts to construct hybrids among the existing methodologies for multiphase flow such as VOF, Level Set, and Front Tracking with the intention of facilitating simulations of general three-dimensional problems. As one of the hybrid method, we have developed the Level Contour Reconstruction Method (LCRM) for general three-dimensional multiphase flows including phase change. The main idea was focused on simplicity and a robust algorithm especially for the three-dimensional case. It combines characteristics of both Front Tracking and Level Set methods. While retaining an explicitly tracked interface using interfacial elements, the calculation of a vector distance function plays a crucial role in the periodic reconstruction of the interface elements in the LCRM method to maintain excellent mass conservation and interface fidelity. In addition, compact curvature formulation is incorporated for the calculation of the surface tension force thereby reducing parasitic currents to a negligible level.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.6
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• pp.443-453
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• 2009

The Rayleigh-Taylor instability, the bubble rising in both partially and fully filled containers and the droplet splash are simulated by an in-house solution code(PowerCFD), which are typical benchmark problems among multiphase flows with material interface due to density difference. The present method(code) employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The present results are compared with other numerical solutions found in the literature. It is found that the present method simulates efficiently and accurately complex free surface flows such as multiphase flows with material interface due to both density difference and instability.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.214-219
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• 2007

Both the bubble rising in a fully filled container and the droplet splash are simulated by a solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method (CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The present results are compared with other numerical solutions found in the literature. It is found that the present code simulate complex free surface flows such as multi phase flows due to large density difference efficiently and accurately.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.99-108
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• 2010

Fractional Step Methods(FSM) are popular in simulation of unsteady incompressible flow. In this study, we demonstrate that FSM, combined with a Volume-Of-Fluid method, can be further applied to simulation of multiphase flow. The interface between the fluids is constructed by the effective least squares volume-of-fluid interface reconstruction algorithm and advected by the velocity using the operator split advection algorithm. To verify our numerical methodology, our results are compared with other authors' numerical and experimental results for the benchmark problems, revealing excellent agreement. The present FSM sheds light on accurate simulation of turbulent multiphase flow which is found in many engineering applications.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.572-575
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• 2008

Two-dimensional multiphase flows due to density difference such as the Rayleigh-Taylor instability problem and the droplet splash are simulated by an in-house solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method in a volume of fluid(VOF) scheme for phase interface capturing. The present results are compared with other numerical solutions found in the literature. It is found that the present code simulates complex free surface flows such as multiphase flows due to density difference efficiently and accurately.

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.21-25
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• 2007

A general purpose program NUFLEX has been extended for two-phase flows with topologically complex interface and cavitation flows with liquid-vapor phase change caused by large pressure drop. In analysis of two-phase flow, the phase interfaces are tracked by employing a LS(Level Set) method. Compared with the VOF(Volume-of-Fluid) method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. Also, the cavitation process is computed by including the effects of evaporation and condensation for bubble formation and collapse as well as turbulence in flows. The volume-faction and continuity equations are adapted for cavitation models with phase change. The LS and cavitation formulation are implemented into a general purpose program for 3-D flows and verified through several test problems.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.187-194
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• 2005

For the analysis of compressible multi-phase and real gas flows, characteristic form of Roe's Riemann solver was derived using real gas equation of state. It was extended to multi component reactive system considering variable specific heat. From this study, it is known that some correction should be made for the use of existing numerical algorithm. 1) Sonic speed and characteristic variable should be corrected with real gas effect. 2) Roe's average was applicable only with the assumption of constant properties. 3) Artificial damping term and characteristic variables should be corrected but their influences may not be significant.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.576-579
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• 2008

Electrical impedance(EIT) for the multi-phase flow visualization is an imaging modality in which the resistivity distribution of the unknown object is estimated based on the known sets of injected currents and measured voltages on the surface of the object. In this paper, an EIT reconstruction algorithm based on the extended Kalman filter(EKF) is proposed. The EIT reconstruction problem is formulated as a dynamic model which is composed of the state equation and the observation equation, and the unknown resistivity distribution is estimated recursively with the aid of the EKF. To verify the reconstruction performance of the proposed algorithm, experiments with simulated multi-phase flow are performed.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.95-102
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• 2017

Debris flow is a composition of solid objects of various sizes, suspension and water, which occurs frequently as the results of landslide following heavy rainfall. This often causes extensive damage in the form of socio-economic losses and casualties as witnessed during the incident around Mt. Umyeon, Seoul in 2011. There have been numerous investigation to mitigate the impacts from debris flow; however, the estimation as preparedness measure has not been successful due to nonlinear and multiphase characteristics of phenomena both in material and process inherent in the debris flow. This study presents a numerical approach to simulate the debris flow using open source code of computational fluid dynamics, OpenFOAM with non-Newtonian viscosity model for three phase material modeling. In order to validate the proposed numerical method, the quantitative evaluations were made by comparisons with experimental results and qualitative analysis for the dispersion characteristics was carried for the case of debris flow in the actual incident from Mt. Umyeon.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.15-22
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• 2018

A compressible multiphase flow was investigated using a DIM consisting of seven equations, including the fifth-order MLP and a modified HLLC Riemann solver to achieve a precise interface structure of liquid and gas. The numerical methods were verified by comparing the flow structures of the high-pressure water and low-pressure air in the shock tube. A 2D air-helium shock-bubble interaction at the incident shock wave condition (Mach number 1.22) was numerically solved and verified using the experimental results.