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여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The intermittent characteristics of fluid particle accelerations near the wall are investigated with the<br/> higher-order statistics and the probability density functions (PDF) by using a direct numerical simulation of<br/> turbulent channel flow. Also, the behaviors of acceleration associated with the coherent structures are<br/> discussed. The flatness factor of wall-normal acceleration is extremely high near the wall and it exceeds the<br/> previously reported value obtained in isotropic turbulence. The presence of the wall seems to make the<br/> accelerations more intermittent and the associated mechanism is explained with the PDFs. The skewness<br/> factor of wall-normal acceleration indicates that accelerations are associated with the streamwise vortices.
정재달(Jaedal Jung),여경민(Kyongmin Yeo),이창훈(Changhoon Lee) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
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, the characteristics of such heavy particles' behavior is quite different from its fluid particles because the inertia force and buoyance force acting on the heavy particles are different than those acting on fluid particles. Therefore, our studies is to investigate the characteristics of the behavior of heavy particles considering the inertia effect with or without gravity effect, but 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 behavior.
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.
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 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.