Ph.D. Students

Donghwi Kim

Donghwi Kim

Name

Donghwi Kim, 김동휘

Course

Ph.D. Candidate  (박사과정)

Research Area

The Navier-Stokes equation, which are now almost universally believed to apply to the physics of all fluid flows (on the assumption for continuum hypothesis). These equations are nonlear and difficult to solve. To solve that governing eqaution, we need to perform the projection method which use ‘Two-step time-advancement scheme’ as the two part of momentum and pseudo-pressure solver. We can obtain the velocity profiles by using the theorem of conservation law to the pseudo-pressure. Using the concept of solver, we can extend that to turbulent flow as well as laminar flow. Priorly, the important properties of fluid are a viscosity and density. The viscosity means that ‘the distance of wall is a critical factor in channel turbulent flows’. The purpose of my basic research is what understand the characteristic of turbulent particle motion near wall, examine turbulent structure in a boundary layer.

 

Local error-u velocity Local error-v velocity Streamline contour Vorticity contour

 

Email

ehdgnl3939@nate.com

Entrance date

2015/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1366

Sangwoo Kang

Name

Sangwoo Kang, 강상우

Course

Ph.D. Candidate  (박사과정)

Research Area

I am interested in theoretical and computational analysis for fluid and heat transfer in the domain with roughness wall by homogenization theory.

Since porous media layer equivalent to surface roughness, I have been studied application of the homogenization theory to Stokes equations in porous media. In the porous media domain, Stokes equation can be changed the Brinkman’s law and Darcy for each size of the hole in the domain.

강상우

Email

swkang87@yonsei.ac.kr

Entrance date

2015/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1359

Soomin Chun

천수민

Name

Soomin Chun, 천수민

Course

Integrated Ph.D Student (통합과정)

Research Area

There are many living things in the water like algae. They need specific material to live, so have tendancy going to position which is high concentration. It can be expressed by Keller-Segel equation. The moving of living things and material effects to the motion of fluid, and vice versa. Considering this, I want to solve combination of Keller-Segel and Navier-Stokes equations. Thesedays there are several problems due to algae or such like that. I hope by doing this research, someday I can expect and warn for the environmental problem. (though I’m solving 1D problem because I’m just a freshman)

Email

catcan@naver.com

Entrance date

2015/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1262

Yoonyeong Choi

 최윤영

Name

Yoonyeong Choi, 최윤영

Course

Integrated Ph.D Student (통합과정)

Research Area

To know some kind of flow  around multiple bodies(like patch of circular cylinders, porous media, vegetation), computation and study about circular patches arrangement. But it needs a lot of computation task and time. So i study multiple body flow for making multiscale modeling and using it.

DNS data about one multiple body is used for making multiscale model.

First, i study vorticity contour and find some small scale influence on big scale. Even one cylinder in patch has steady flow, patch has unsteady flow.

Second, each multiscale domain has averaged DNS data . Using this data , i make some equations using Multiple Linear Regression Analysis.

And i evaluate how much data from these equations accord DNS data.

최윤영-research 최윤영-research2

Email

choi2223@naver.com

Entrance date

2015/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1253

Xiang Sun

Xiang Sun

Name

Xiang Sun

Course

Ph. D. Student (박사과정)

Research Area

Uncertainty quantification (UQ) is both a new field and one that is as old as the disciplines of probability and statistics. The present novelty lies in the synthesis of probability, statistics, model development, mathematical and numerical analysis, large-scale simulations, experiments, and disciplinary sciences to provide a computational framework for quantifying input and response uncertainties in a manner that facilitates predictions with quantified and reduced uncertainty.

My interest is to study the UQ in CFD. I am trying to study how to model uncertainty and stochastic inputs, and how to formulate algorithms to accurately reflect the propagation of the uncertainty in CFD, such as modeling the input uncertainty and its propagation in incompressible flow simulations, quantifying the epistemic uncertainties in RANS model and so on.

Email

sxltlg2312@gmail.com

Entrance date

2014/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1268

Seulgi Lee

 이슬기

Name

Seulgi Lee 이슬기

Course

Ph. D. Student (박사과정)

Research Area

Suspended particles in a turbulent flow can be observed in a nature phenomenon found atmosphere, ocean and a lot of industrial applications, many of which are making air pollution, water pollution such as environmental issues and engineering problems. Thus it is very important to expect behavior of the suspended particles.

I have been studying Isotorpic turbulence and homogeneous shear turbulence. Using direct numerical simulation (DNS). I am trying to explain behavior of suspended particles in homogeneous shear turbulent or isotropic turbulent.

이슬기-research

Email

sg.lee@yonsei.ac.kr

Entrance date

2014/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=989

Seungho Song

송승호

Name

Seungho Song, 송승호

Course

Ph.D. Student (박사과정)

Research Area

The blast wave from the detonation of a nuclear explosion is studied based on results of a numerical calculation in two dimensions. The 2D blast wave propagation carries out by solving the Euler equation. The piecewise parabolic method (PPM) and the approximate riemann solver (Roe’s method) are used to discretize inviscid fluxes. We performed the initial condition blast waves by using the one dimensional radiation hydro-dynamics (RHD) at the breakaway that the blast waves are firstly came into view on the surface of the fireball. The new method is proposed to get the second order accuracy in the 1D-RHD which is coupling radiation and hydro-dynamics. The method makes to improve the initial blast wave values. Characteristics of the blast wave propagations are investigated because of the various heights and amount of the nuclear detonations.

송승호-research

Email

seunghosong@yonsei.ac.kr

Entrance date

2014/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=796

Seongjin Won

원성진

Name

Seongjin Won, 원성진

Course

Integrated Ph.D Student (통합과정)

Research Area

There are various ways to express virtual object in Computational Domain. One of the efficient methods is Immersed Boundary Method (IBM). IBM makes virtual object in flow field with setting lagrangian points on the virtual object and calculates forcing on the eulerian and lagrangian points. I studied basic of Immersed boundary method and calculating temperature in laminar flow. And it is adopted my undergraduate research paper.

Also these days, studying Large Eddy Simulation (LES) in 3D turbulent channel flow is my new research area. LES is calculate flow field with turbulent modelling and it is different with DNS. Direct Numerical Simulation (DNS) means just calculate flow filed without modelling. So it needs huge amount of grid to resolve small size turbulent motions. The advantage of LES is using less number of grids which means calculation costs is effectively saved. For the nice approach, more effective turbulent modelling’s are needed. There are various kinds of models to predict turbulent motions of sub grid scales. My research will be applying various LES models to real world turbulent phenomena for prediction with cost efficiency.

원성진-research1 원성진-research2

Email

sjwon1991@nate.com

Entrance date

2014/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1065

Kiha Kim

김기하

Name

Kiha Kim, 김기하

Course

Integrated Ph.D Student (통합과정)

Research Area

Understanding of interactions between an oscillating circular cylinder and wake flows is very important in many engineering problems such as structural applications, bluff body dynamics, etc. The objective of my study is to characterize the interactions between an arbitrary oscillating circular cylinder wake and uniform stream. Especially, our aim is to analyze the lock-in region in terms of oscillation conditions and to find a linear relation for the aerodynamic forces with respect to the oscillation direction.

We extended the semi-implicit projection method in a Cartesian coordinate to cylindrical coordinate. In addition, the Fourier diagonalization scheme was used for Poisson equation.

The result shows that the drag coefficient increases as the cross-flow angle increases. Local extrema for the drag coefficients are observed when the forced frequency is closed to natural frequency. And result indicates that a strong linearity of the drag coefficients for the oscillation directions in the lock-in region.

김기하-research

Email

k-kiha@yonsei.ac.kr

Entrance date

2014/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1058

Sajjad ur Rehman

Sajjad

Name

Sajjad ur Rehman

Course

Ph.D Student (박사과정)

Research Area

Study of Isotropic turbulence

The term “turbolenze ” is first introduce by an Italian mathematician, engineer Leonardo da Vinci 500 years ago. Initially turbulence is considered as random process. The first attempt is done in 1930s by G. I. Taylor who introduced statistical methods involving correlation, Fourier transform and power spectra into turbulence literature. Then in 1941 Russian statistician A. N. Kolmogorov published three papers that provide some important and most-often quoted results of turbulence theory.

Statistically Homogenous Turbulence is that in which all statistics of fluctuating quantities are invariant under translation of the coordinate system. Scalar dissipation rate in statistically homogenous turbulence is look like as,

Statistically Isotropic turbulence is that in which all statistics are invariant under translation, rotation and reflection of coordinate system. In this case mean velocities are zero. Simplifications allow theoretical conclusions about turbulence. Turbulent motions on small scales are typically assumed to be isotropic (Kolmogorov hypotheses).

Numerical treatment for Isotropic turbulence:

In order to solve isotropic turbulence problem Direct Numerical Simulation (DNS) is used. This method is first introduced by Orszag and Patterson in 1970. In this method Naiver-Stokes equations are solved without any turbulence model. DNS is performed with and without using Pseudo-Spectral methods. Initial conditions can be controlled in such simulations. First convert Naiver-Stokes equation into rotational form by replacing a nonlinear term by a relationship. Pressure Possion equation is used to eliminate pressure. Then by applying Fourier series all derivatives are expanded. Viscous terms are solved analytically. For temporal discretization a low storage 3rd –order 3-stage Runge-Kutta scheme is applied. Nonlinear terms are solved by using Pseudo-spectral method. External forcing is necessary to maintain turbulence. Stochastic spectral scheme as proposed by Eswaren and Pope is used.

Eulerian Statistics are calculated other interesting results for example one dimensional spectra, structure functions and correlation function are calculated.

Sajjad-research-RMS_VELFigure 1. RMS(Root mean square) VelocitySajja-research-1D_energy_spectraFigure 2. 1D Energy Spectrum

Email

sajjadqau2@gmail.com

Entrance date

2013/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1061

Geunwoo Oh

오근우

Name

Geunwoo Oh, 오근우

Course

Integrated Ph.D Student (통합과정)

Research Area

Understanding of flow over a bluff body is very important in various aerodynamic designs. Wake patterns behind a bluff body are associated with its geometric configurations, which leads to variations of aerodynamic characteristics. Since the orientation of the elliptic cylinder to cross flows introduces asymmetric wake patterns, it is worthy to investigate the change of the aerodynamic characteristics due to the angle of attack. The objective of the present study is to investigate the effect of geometric configurations of elliptic cylinder on aerodynamic forces and to provide general correlations between the configurations and the force coefficients.오근우-research

 

Email

genugenu@naver.com

Entrance date

2013/08

Permanent link to this article: http://euler.yonsei.ac.kr/?p=1040

Hojun Lee

이호준

Name

Hojun Lee, 이호준

Course

Integrated Ph.D Student (통합과정)

Research Area

The motion of particles in turbulence is often seen in air and water flows and also occurs in many engineering application. Because a solid particle is generally modeled as a sphere, it is important to understand the flow over a sphere. Solid particles in a flow both translate and rotate simultaneously. In particle laden turbulence, the rotation in the streamwise or transverse direction may be induced by inter-particle interactions. Therefore, it is important to understand the effect of rotation on the flow.

The characteristics of flow over a sphere depend significantly on the direction of rotation. One is the transverse direction, where the axis of rotation is orthogonal to that of translation. the other is the streamwise direction, where the rotational direction is the same as that of translation.

 

cp_80D20D

Email

macros21@yonsei.ac.kr

Entrance date

2013/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=446

Xiaomin Pan

Xiaomin Pan

Name

Xiaomin Pan

Course

Integrated Ph.D Student (통합과정)

Research Area

Various projection methods have been widely studied and used for time-dependent incompressible Navier–Stokes equations, and stability and accuracy properties are the key issues for investigating the performance of projection methods. The present study focus on analyzing the stability property and temporal accuracy of the implicit projection methods, linearized convection projection method and velocity decoupled projection method, based on Kim et al.’s work (2002, An implicit velocity decoupling procedure for the incompressible Navier–Stokes equations). In the linearized convection projection method, the Crank–Nicolson scheme is used for both the convection and diffusion terms with a block LU decomposition employed for pressure-velocity decoupling. For avoiding the iterative procedure, based on the linearized convection projection method, additional decoupling procedure is applied to the intermediate velocity components which leads to the velocity decoupled projection method. Three types of discrete operators, advective, skew-symmetric and divergence operators are is used for the nonlinear convection term.

We prove that the two methods are second-order accurate in time by evaluating the differences between the numerical solutions and Crank–Nicolson solutions (solutions without any decoupling procedure) for velocities and pressure in discrete L2-norm. We present the stability properties of the two methods via estimating the kinetic energy estimation for fully-discrete Navier-Stokes equations which confirms almost unconditionally stability of the methods and performing the von Neumann analysis of linearized Navier-Stokes equations for getting the distribution of maximum magnitude of the eigenvalues for the corresponding matrix. The influences of three discrete operators are considered in the theoretical discussion. Finally, we consider 2D lid-driven cavity flow and periodic forced flow to validate the theoretical assertions.

[Simulations based on the lid-driven cavity flow]

Re=100, CFL=130

Re=100 and CFL=130

Re=100, CFL=130Re=400 and CFL=115

[Simulations based on the periodic forced flow]

velocity decoupled method

Linearized convection method

Linearized convection method Velocity decoupled method

Email

sanhepanxiaomin@gmail.com

Entrance date

2012/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=958

Juwon Jang

장주원

Name

Juwon Jang, 장주원

Course

Integrated Ph.D Student (통합과정)

Research Area

Particle laden turbulent channel flow simulation by using Immersed boundary method

In the nature, We can easily see moving particles in the air or liquid in our life. We use particles to improve our living life and to get the safety. For example, We make the spring cooler to put out the fire. And we use solid fuel particles in a rocket and so on.

Many researchers have studied about the particle in the fluid to understand how particle move, react, collide. To study about the particle, we can approach through the experiment or simulation. When we simulate the particle motion, Immersed boundary method is the popular method. By using this method, we can easily represent the particle motion in the fluid dynamic simulation like picture.

Recently, I am developing the fully resolved particle laden turbulent channel flow by using immersed boundary method and the parallel computing.

 

장주원-research

Email

deicity@naver.com

Entrance date

2012/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=799

Ki young, Moon

Ki young, Moon (문기영)

Ph.D. candidate

Research area: Turbulence Model, Urban Flow

 

Email: moon7711@paran.com

Permanent link to this article: http://euler.yonsei.ac.kr/?p=428

Jongsu Kim

김종수

Name

Jongsu Kim, 김종수

Course

Integrated Ph.D Student (통합과정)

Research Area

There are numerous theories to describe the process of rain, it is not enough to explain. According to observation, a rainfall from the rapidly formed hot cloud, like squall or shower, comes down more faster than theory. For hot cloud, droplet collision is a dominant process of rainfall.
I’m studying a droplet collision. Using level set method, I’m trying to explain a relationship between droplets. I made a level set solver and now implement Navier-Stokes equation solver in incompressible multi-phase flow. I will validate my results with experiments and extend to many droplet collision cases. Here is a result of my level set solver (Zalesak’s disk) and it seems good at preserving its interface with rotating flow despite of large curvature at some points.

김종수-research

Figure 1. Zalesak disk, high curvatured slotted disk in rotating flow

Email

skyobserver@yonsei.ac.kr

Entrance date

2011/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=356

Battsetseg Gereltbyamba

Battsetseg Gereltbyamba

Name

Battsetseg Gereltbyamba

Course

Ph.D. Student (박사과정)

Research Area

Problem and areas I am working Direct Numerical Simulation (DNS) of natural convection in a differentially heated air filled cavity. Natural convection is one kind of heat transport without any external force but only by presence of a temperature gradient. This problem is importance in many engineering and science applications such as air flow in building, thermal insulation, room ventilation and solar energy devices.
Natural convection of air is observed within a cubic cavity with the assumption two opposite vertical walls are differentially heated, and four other walls are insulated. Governing equations of problem are a system of nonlinear partial differential equation and no general analytic solution. Therefore we should be solving numerically using some assumptions. Direct numerical simulation was performed via a projection method which is proposed by Kim and Moin. In this simulation we are observing effect of Rayleigh number which flows become laminar, periodic and quasi periodic and chaotic respectively. Some flow dynamic results related to turbulent statistics and heat transfer rate, velocities and temperature distributions are simulated.

Email

battsetseg_g@yahoo.com

Entrance date

2011/09

Permanent link to this article: http://euler.yonsei.ac.kr/?p=345

Weiwei Fang

Name

Weiwei Fang

Course

Integrated Ph.D Student (통합과정)

Research Area

Plane Couette flow is attractive for developing theoretical models for turbulence and for hydrodynamic stability, because of the simplicity of the governing equation and the geometry. Plane Couette flow is caused by the motion of two parallel infinite planes in directions opposite to each other (see Figure 1 and Figure 2). The mean pressure gradient of the Couette flow is zero and the driving force is a constant shear stress transmitted through the fluid from one plane to the other. A fully developed plane Couette flow has a constant shear stress, across the entire channel for both laminar and turbulent.

The simulation is made using pseudo-spectral method with Fourier and Chebyshev polynomial expansion in horizontal plane and vertical direction. In order to eliminate alias error, the -rule is employed in horizontal directions and not employed in the vertical direction because of the incompatibility with the no-slip boundary condition at the wall.

Email

fwwatqd@gmail.com

Entrance date

2011/09

 

Permanent link to this article: http://euler.yonsei.ac.kr/?p=421

Junghoon Lee

이정훈

Name

Junghoon Lee, 이정훈

Course

Ph.D. Candidate (박사과정)

Research Area

Particle-laden turbulence,

A knowledge of turbulent flows laden with small, inertial particles is of importance in understanding and predicting many industrial and geophysical flows, such as chemical reactors, aerosols in atmosphere and sediment transport. Such particle-laden turbulence is investigated by using direct numerical simulation coupled with Lagrangian particle tracking. In particular, turbulence modification by particles, inter-particle collisions and particle-wall interactions are my main research fields.

이정훈-research

Email

j.h.lee@yonsei.ac.kr

Entrance date

2011/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=432

Hyunwook Park

박현욱

Name

Hyunwook Park, 박현욱

Course

Integrated Ph.D Student (통합과정)

Research Area

Understanding of flow over a bluff body is very important in various aerodynamic designs. Wake patterns behind a bluff body are associated with its geometric configurations, which leads to variations of aerodynamic characteristics. Since the orientation of the elliptic cylinder to cross flows introduces asymmetric wake patterns, it is worthy to investigate the change of the aerodynamic characteristics due to the angle of attack. The objective of the present study is to investigate the effect of geometric configurations of elliptic cylinder on aerodynamic forces and to provide general correlations between the configurations and the force coefficients.

박현욱-research

Email

deukgyun@naver.com

Entrance date

2011/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=604

Sangro Park

박상로

Name

Sangro Park, 박상로

Course

Integrated Ph.D (통합과정)

Research Area

Rayleigh-Bénard convection is a natural convection frequently observed in our environment, like boiling water, atmospheric convection, etc. Therefore it causes many interesting phenomena: convective spreading of dust particles, cloud formation and cooling of industrial devices. Simulation of particle-laden Rayleigh-Bénard convection with pseudo-spectral method is one of the most important ways to analyze the phenomena. Especially, we study inertial particles in Rayleigh-Bénard convection with significant considerations of interactions between coherent flow structures and particles. The figures show particle accumulation affected by thermal structures in Rayleigh-Bénard convection.

박상로-research1-St1_xy

Figure 1. Side view of domain with temperature contour and particle distribution

박상로-research1-St1_xz

Figure 2. Over view of domain with temperature contour and particle distribution

Email

psr4109@naver.com

Entrance date

2010/03

Permanent link to this article: http://euler.yonsei.ac.kr/?p=430