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정재달(Jaedal Jeong),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Particle-laden turbulence is frequently observed in nature such as the atmosphere and ocean, as well as in many engineering flows. Recently, as the dispersion of pollutant in environmental problem is of more interest, the study on the particle-laden turbulence is more important both for predicting the behavior of particles and for understanding the fundamental characteristics. Isotropic turbulence is a good example of turbulence for understanding its the properties because if Reynolds number is high, small scale turbulence has universal characteristics of isotropic turbulence without relevance to large scale turbulence. Thus, using direct numerical simulation of particle-laden isotropic turbulence, we investigate the correlation of fluid velocities along particle trajectories for finding fluid-particle interaction mechanism. Furthermore, the results of present study can be applied to development of a solid particle dispersion model.
조성기(Seonggee Cho),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
The motion of small heavy particles in homogeneous isotropic turbulence in the present of gravity is investigated using Direct Numerical Simulations (DNS) at moderate Reynolds number. The Lagrangian velocity and acceleration statistics of particles and of flow for a wide range of Stokes number, defined as the ratio of the particle response time to Kolmogorov time scale of turbulence, were obtained for the direction of the gravity and normal direction, respectively. It is found that particles lose their correation faster than the case without gravity. Then, a significant increase in the average settling velocity was observed for a certain range of Stokes number. Our focus is placed on gravitational effect on very small particles. Our simulations show that as the Stokes number reduces to zero, their mean settling velocity aproaches the terminal velocity in still fluid.
정재달(Jaedal Jeong),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Particle suspension is frequently observed in many natural flows such as in the atmosphere and the ocean as well as in various engineering flows. Recently, airborne micro or nano-scale particles in atmosphere attract much attention from environmental society since small particle cause serious environmental problems in the industrialized areas. Also, such heavy particles' behavior is quite different from its pure fluid particles because the inertia force and buoyance force acting on the heavy particles are different than those acting on fluid particles, so that heavy particles do not follow the trajectories of the fluid particle. Therefore, our studies is to investigate the characteristics of the behavior of heavy particles considering the inertia effect under gravity. However, we do not consider modification of turbulence by the particles, that is one-way interaction. We carried out direct numerical simulation of isotropic turbulence with particles under the Stokes drag assumption for a spherical particle. These results can be used in the development of a stochastic model for predicting particle's dispersion.
심기훈(G.H. Shim),이슬기(S.G. Lee),이창훈(C. Lee) 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.4
Direct numerical simulation is conducted to observe the behavior of microbubbles in isotropic turbulence. Navier-Stokes equation and the motion of equation for microbubbles are solved with periodic boundary condition in a cube domain. Vorticity contour, enstrophy ratio, relative reduction of bubble rise velocity, and the closest distance of particles are investigated for various Stokes numbers and gravity factors to understand clustering of microbubbles. Also, clustering due to the effect of the lift force is investigated.
중력을 고려한 등방성 난류에서 다양한 스토크수에 따른 입자의 유동
정용락(Yongrak Jung),박용남(Yongnam Park),이창훈(Changhoon Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4
The motion of particles with various Stokes numbers in homogeneous isotropic turbulence in the present of gravity is investigated using Direct Numerical Simulations (DNS) at moderate Reynolds number. The Lagrangian velocity and acceleration statistics of particles and of flow for a wide range of Stokes number, defined as the ratio of the particle response time to Kolmogorov time scale of turbulence, were obtained for the direction of the gravity(vertical or settling) and normal direction, respectively. It is found that particles and fluid lose their correation faster with the Reynolds number. Our focus is placed on gravitational effect on very small particles. Our simulations show that as the Stokes number reduces to zero, their mean settling velocity approaches the terminal velocity in still fluid.
최연택(Yeontaek Choi),이창훈(Changhoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
We investigated the intermittent property of helicity of the isotropic turbulence. As well known, helicity is a quadratic invariant on the inviscid Navier-Stokes flows. But unfortunately it has no invariance in the viscous fluids. Furthermore, it has a intermittent fashion through its cascade in the inertial range. We looked for the sources to raise this intermittency, handling with local quantities such as local enstrophy, dissipation, and local coupling angle of velocity and vorticity. It seems to be the preferred angles to determine the direct relation between local velocity and local vorticity, and to be guessed the source of the intermittency.
김지연(Jiyeon Kim),이창훈(Changhoon Lee) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11
The denoising diffusion probabilistic model (DDPM), a recent addition to the landscape of generative models, has demonstrated remarkable performance comparable to state-of-the-art methods like generative adversarial networks (GANs) across various applications. Despite emerging only in 2020, DDPM has been subject to extensive research efforts aimed at refining both its model performance and cost efficiency. However, uncertainties linger regarding its applicability to diverse tasks involving turbulence data or flow field data. This study aims to present the outcomes of applying a basic DDPM to a relatively simple task of generating 2D isotropic turbulence from Gaussian noise and to validate the feasibility of DDPM in handling fluid dynamics data through rigorous quantitative and qualitative analyses on the results. Additionally, we outline directions for future development, involving enhancements for applying to other tasks to the backbone DDPM model.