• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.27.1-27.1
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• 2015

천문학적 유체는 대부분 자기장을 가지고 있으며 난류상태에 있다고 믿어진다. 본 발표에서는 다양한 환경에서 존재하는 자기유체역학적(MHD) 난류를 소개하고자 한다. 첫째, 가장 간단한 경우로 비압축성 유체에서 발생하는 MHD 난류를 살펴보고자 한다. 이 경우, 평균자기장의 세기가 약한 경우와 강한 경우로 나누어 볼 수가 있는데, 평균자기장의 세기가 아주 약한 경우 난류에 의한 자기장의 증폭 현상이 특히 중요하다. 평균자기장의 세기가 강한 경우는 난류의 스펙트럼과 구조가 큰 관심사가 되고 있다. 둘째, 작은 스케일 난류와 초음속 압축성 난류를 간단히 소개하고자 한다. 작은 스케일(이온의 자이로 반경 부근) 난류는 아직 연구가 미진한 분야 중 하나이고 초음속 압축성 난류는 해석적 연구가 어렵기 때문에 연구의 많은 부분을 수치계산에 의존하고 있다. 마지막으로, MHD 난류에 대한 지식이 어떻게 관측에 응용될 수 있는지 간단한 예를 들고자 한다.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.48.1-48.1
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• 2005

• Proceedings of the Korea Society for Simulation Conference
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• 1999.04a
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• pp.133-137
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• 1999

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.43.1-43.1
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• 2005

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.389-396
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• 2010

In this paper, a new computational code was developed using Chorin's artificial compressibility method to solve the two-dimensional incompressible Navier-Stokes equations. In spatial derivatives, Roe's flux difference splitting was used for the inviscid flux, while central differencing was used for the viscous flux. Furthermore, AF-ADI with dual time stepping method was implemented for accurate unsteady computations. Two-equation turbulence models, Menter's $k-{\omega}$ SST model and Coakley's $q-{\omega}$ model, hae been adopted to solve high-Reynolds number flows. A number of numerical simulations were carried out for steady laminar and turbulent flow problems as well as unsteady flow problem. The code was verified and validated by comparing the results with other computational results and experimental results. The results of numerical simulations showed that the present developed code with the artificial compressibility method can be applied to slve steady and unsteady incompressible flows.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.614-617
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulations of three dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence free flow field at each physical time step. The one equation Spalart-Allmaras turbulence model has been adopted to solve the high-Reynolds number flow fields. This method has been applied to calculate the steady flow fields around submarine configurations and unsteady flow fields around a 3-D infinite cylinder.

• Journal of computational fluids engineering
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• v.17 no.3
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• pp.99-107
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• 2012

In this paper, the shock waves in compressible solids and liquids are simulated using a six-equation diffuse interface multiphase flow model that is extended to the Cochran and Chan equation of state. A pressure relaxation method based on a volume fraction function and a pressure-correction equation are newly implemented to the six-equation model. The developed code has been validated by a shock tube problem with liquid nitromethane and an impact problem of a copper plate on a solid explosive. In addition, a new problem, an impact of a copper plate on liquid nitromethane, has been solved. The present code well shows the wave structures in compressible solids and liquids without any numerical oscillations and overshoots. After the impact of a solid copper plate on liquid, two shock waves (one propagates into liquid and the other into solid) are generated and a material interface moves to the impacting direction. The computational results show that the shock velocity inside the liquid linearly increases with the impact velocity.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.9-16
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• 2013

Cavitation on an axi-symmetric hemispherical head-form body was studied using an Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. To consider compressibility effects on the vapor phase and cavity interface, a pressure-based compressible flow CFD code was developed. To validate the developed CFD code, cavitating flow around the hemispherical head-form body was simulated using pressure-based incompressible and compressible CFD codes and validated against existing experimental data in the three-way comparison. The cavity shedding behavior, length of re-entrant jet, drag history, and Strouhal number of the hemispherical head-form body were compared between two CFD codes. The results, in this paper, suggested that the computations of cavitating flow with compressibility effects improve the description of cavity dynamics.

• Journal of computational fluids engineering
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• v.19 no.3
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• pp.85-90
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• 2014

The purpose of this study is to develop a new Meshless Method to solve 2-D compressible flow problems numerically. This paper includes a revised Least Square method that improves robustness compared with its original version by removing excessive numerical oscillation which occurs when points are randomly distributed. Numerical analyses of hypersonic flow over a blunt body were carried out using the method, then robustness, accuracy and convergence of their results were compared with those obtained from the original method.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.223-232
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• 1998

To investigate the flow inside the centrifugal impeller, computer program which can solve Three-dimensional compressible turbulent flow has been developed. The Navier-Stokes equations were chosen as the governing equation for viscous flow while Euler equations for inviscid case. Time marching method was incorporated with the Flux Difference Splitting method suggested by Roe to capture the steep gradients such as a shock. For high order of accuracy, MUSCL approach was adopted while differentiable limiter to ensure TVD property. For turbulence closure, Baldwin- Lomax model was applied due to its simplicity. To demonstrate the capabilities of present program, several validation problems have been solved and compared with experiments and other available data. From the above calculations generally good agreements were obtained. Finally, the developed code was applied to Eckardt's impeller and the performance prediction was carried out. Some important aspects on boundary condition for successful simulation were discussed and the remedy was also introduced.