원형 단면을 갖는 180° 굽은 곡관내 발달하는 난류유동에 관한 수치해석

명현국,Myong Hyon-Kook 대한기계학회 2006 大韓機械學會論文集B Vol.30 No.10

A numerical simulation is performed fur developing turbulent flow in a strongly curved 180 deg pipe and its downstream tangent by a new solution code(PowerCFD) which adopts an unstructured cell-centered method. The governing equations are discretized as the full elliptic from of the equations of motion. Three typical two-equation turbulence models of low-Reynolds-number form are used to approximate the turbulent stress field. Solutions fur both streamwise and circumferential velocity components are compared with the experimental data by Azzola et at.(1986). The ${\kappa}-{\omega}$ model by Wilcox(1988) is found to give better prediction performance than the other two. Predicted secondary velocities and streamwise velocity component contours at sequential longitudinal stations are also presented in order to enable a detailed description of the complete flow. It is also found that, in the bend both mean streamwise and secondary velocities never achieve a fully-developed state and the code is capable of producing very well the complex nature of steady flow in a strongly curved pipe.

난류에 의해 야기되는 이차유동 예측성능에 대한 비선형 κ-ε 난류모델의 평가

명현국,Myong, Hyon-Kook 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.8

Nonlinear relationship between Reynolds stresses and the rate of strain of nonlinear k-$\varepsilon$models is evaluated theoretically by using the boundary layer assumptions against the turbulence-driven secondary flows in noncircular ducts and then their prediction performance is validated numerically through the application to the fully developed turbulent flow in a square duct. Typical predicted quantities such as mean axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared with available experimental data. The nonlinear k-$\varepsilon$ model adopted in a commercial code is found to be unable to predict accurately duct flows with the prediction level of secondary flows one order less than that of the experiment.

비선형 저레이놀즈수 κ-ε 난류모델에 따른 정사각형 덕트내 완전 발달된 난류유동 예측

명현국,Myong, Hyon-Kook, 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.6

Fully developed turbulent flow in a square duct is numerically predicted with two nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ models. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in detail with each other. It is found that the nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ model adopted in a commercial code is unable to predict accurately duct flows involving turbulence-driven secondary motion with the prediction level of secondary flows one order less than that of the experiment.

고속전철 객실의 공기 분배 및 기류에 관한 수치해석적 연구

명현국,유경훈,황정호,Myong, Hyon-Kook,Yoo, Kyung-Hoon,Hwang, Jungho 한국입자에어로졸학회 2019 Particle and Aerosol Research Vol.15 No.1

Numerical analysis has been conducted on three-dimensional airflow distribution in the passenger cabin of a high-speed electric train. The types of air distribution systems investigated in the present study were those of TGV and Shinkansen. The Reynolds-averaged Navier-Stokes equations governing the mass and momentum conservations of the airflow in the cabin were solved by using a finite volume method, which are coupled with the standard $k-{\varepsilon}$ turbulence model equations. Predicted velocity distributions were presented on several selected planes in the passenger cabin. The present three-dimensional simulations were found to show the overall features of the airflow in the passenger cabin fairly well. In particular, it was shown that the type of air distribution for Shinkansen was more suitable for a non-smoking cabin than that for TGV.

다양한 조건하에서 모세관력 불균형에 의해 구동되는 수평 표면 위의 액적 거동

명현국(Hyon Kook Myong),권영후(Young Hoo Kwon) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.4

본 연구는 다양한 조건하에서 모세관력 불균형에 의해 구동되는 수평 표면 위의 액적 거동을 수치해석적으로 연구한 것이다. 액적 거동은 자체개발 코드(PowerCFD)를 사용하여 수치해석하였다. 수치해석에 사용된 코드는 보존적인 압력기반 유한체적방법에 기초한 비정렬 셀 중심 방법 및 VOF 방법에 체적포착법인 CICSAM을 채용하고 있다. 상세한 액적 거동이 다양한 초기 액적형상, 접촉각 및 표면장력(또는 Bond 수)의 조건하에서 얻어졌다. 또한 액적 이송 메커니즘이 액적 형상에 대한 수치해석 결과로부터 검토되었다. The present study aims to numerically investigate the behavior of liquid droplet driven by capillarity force imbalance on horizontal surfaces ranging from hydrophilic to hydrophobic, under various conditions. The droplet behavior has been simulated using an in-house solution code(PowerCFD), which 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 detailed droplet behavior was obtained under various conditions for droplets with different initial shapes, contact angles and surface tension forces(or Bond number). The mechanism of droplet transport was examined using the numerical results on the droplet shapes.

OOP 개념에 기초한 유동해석용 후처리 프로그램 개발

명현국(Hyon Kook Myong),안종기(Jong Ki Ahn) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.1

A post-processing program based on the OOP(Object-Oriented Programming) concept has been developed for flow visualization of the flow analysis code(PowerCFD) using unstructured cell-centered method. User-friendly GUI(Graphic User Interface) has been built on the base of MFC(Microsoft Foundation Class). The program is organized as modules by classes including those based on VTK(Visualization ToolKit)-library, and these classes are made to function through inheritance and cooperation which is an important and valuable OOP concept. The major functions of this post-processor program are introduced and demonstrated, which include mesh plot, contour plot, vector plot, surface plots, cut plot, clip plot, xy-plot and streamline plot as well as view manipulation (translation, rotation, scaling etc).

유동해석용 후처리 프로그램 개발

명현국(Hyon Kook Myong),안종기(Jong Ki Ahn) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

A post-processing program based on the OOP(object-oriented programming) concept has been developed for flow visualization of the flow analysis code(PowerCFD) using unstructured cell-centered method. User-friendly GUI(graphic user interface) has been built on the base of MFC(Microsoft Foundation Class). The program is organized as modules by classes based on VTK-library, and these classes are made to function through inheritance and cooperation which is an important and valuable concept of object-oriented programming. The major functions of this post-processor program are introduced and demonstrated, which include mesh plot, contour plot, vector plot, surface plots, cut plot, clip plot, xy-plot, animation and streamline plot as well as view manipulation (translation, rotation, scaling etc).

OOP 개념에 기초한 유동해석용 전처리 프로그램 개발

명현국(Hyon Kook Myong),안종기(Jong Ki Ahn) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.1

A pre-processing program based on the OOP(object-oriented programming) concept has been developed. The program consists of the input of a 2D or 3D flow problem to a CFD program by means of an user-friendly interface and the subsequent transformation of this input into a form suitable for the solver(PowerCFD) using unstructured cell-centered method. User-friendly GUI(graphic user interface) has been built on the base of MFC(Microsoft Foundation Class). The program is organized as modules by classes based on VTK(Visualization ToolKit)-library, and these classes are made to function through inheritance and cooperation which is an important and valuable concept of object-oriented programming. The major functions of this program are introduced and demonstrated, which include mesh generation, boundary settings, solver settings, generation of grid connectivity and geometric data etc.

벽면부착에 의해 야기되는 다상유동에 관한 수치적 연구

명현국(Hyon Kook Myong) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.7

본 연구에서는 벽면부착에 의해 야기되는 다상유동에 대한 수치적 연구를 제시한다. 먼저 다상유동 해석을 위해 표면장력에 대한 CSF(Continuum Surface Force) 모델 및 벽면부착 경계조건 모델을 비정렬격자계에 적합하도록 수치해석방법을 정립시키고, Myong(2009)이 개발한 비정렬격자계와 VOF 방법으로 체적포착법(volume capturing method)을 사용한 수치해석방법(코드)에 삽입하였다. 또한 본 수치해석방법을 사용하여 중력을 포함하여 어떤 외력도 존재하지 않고 오직 벽면부착에 의해 야기되는 유동현상인 원통형 탱크의 바닥에 위치한 얕은 물풀(water pool)에 대해 물이 벽면을 적시는 경우와 적시지 않는 경우에 대해 수치해석 하였다. 연구결과, 본 수치해석방법은 벽면부착에 의해 야기되는 다상유동 문제에 대한 유용성이 입증되었다. The present paper presents a numerical study on multiphase flows induced by wall adhesion. The continuum surface force (CSF) model with the wall adhesion boundary condition model is used for calculating the surface tension force; this model is implemented in an in-house solution code (PowerCFD). The present method (code) employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with a volume capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. The effects of wall adhesion are then numerically simulated by using the present method for a shallow pool of water located at the bottom of a cylindrical tank with no external forces such as gravity. Two different cases are computed, one in which the water wets the wall and one in which the water does not wet the wall. It is found that the present method efficiently simulates the surface tension-dominant multiphase flows induced by wall adhesion.

유동해석용 전처리 프로그램 개발

명현국(Hyon Kook Myong),안종기(Jong Ki Ahn) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

A pre-processing program based on the OOP(object-oriented programming) concept has been developed, which consists of the input of a 2D or 3D flow problem to a CFD program by means of an user-friendly interface and the subsequent transformation of this input into a form suitable for use by the solver(PowerCFD) using unstructured cell-centered method. User-friendly GUI(graphic user interface) has been built on the base of MFC(Microsoft Foundation Class). The program is organized as modules by classes based on VTK-library, and these classes are made to function through inheritance and cooperation which is an important and valuable concept of object-oriented programming. The major functions of this program are introduced and demonstrated, which include mesh generation, boundary settings, solver settings, generation of grid connectivity and geometric data etc.