• 한국전산유체공학회:학술대회논문집
• /
• 2003.08a
• /
• pp.43-48
• /
• 2003

When the Eulerian-Lagrangian method is used to analyze the particle laden two-phase flow, a large number of particles should be used to obtain statistically meaningful solutions. Then it takes too much time to track the particles and to average the particle properties in the numerical analysis of two-phase flow. The purpose of this paper is to reduce the computation time by means of a set of particle gird separate to the flow grid. Particle motion equation here is the simplified B-B-O equation, which is integrated to get the particle trajectories. Particle turbulent dispersion, wall collision, and wall roughness effects are considered but the two-way coupling effects between gas and particles are neglected. Particle laden 2-D channel flow is solved and it is shown that the computational efficiency is indeed improved by using the current method

• Journal of Korean Society for Atmospheric Environment
• /
• v.15 no.6
• /
• pp.757-765
• /
• 1999

Lagrangian particle dispersion model(LPDM) is an effective tool to calculate the dispersion from a point source since it dose not induce numerical diffusion errors in solving the pollutant dispersion equation. Fictitious particles are released to the atmosphere from the emission source and they are then transported by the mean velocity and diffused by the turbulent eddy motion in the LPDM. The concentration distribution from the dispersed particles in the calculation domain are finally estimated by applying a particle count method or a Gaussian kernel method. The two methods for calculating concentration profiles were compared each other and tested against the analytic solution and the tracer experiment to find the strength and weakness of each method and to choose computationally time saving method for the LPDM. The calculated concentrations from the particle count method was heavily dependent on the number of the particles released at the emission source. It requires lots fo particle emission to reach the converged concentration field. And resulting concentrations were also dependent on the size of numerical grid. The concentration field by the Gaussian kernel method, however, converged with a low particle emission rate at the source and was in good agreement with the analytic solution and the tracer experiment. The results showed that Gaussian kernel method was more effective method to calculate the concentrations in the LPDM.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.1851-1856
• /
• 2003

A new Lagrangian stochastic dispersion model is developed by combining the GLM(generalized Langevin model) and the elliptic relaxation method. Under the physically plausible assumptions a simple analytical solution of elliptic relaxation is obtained. To compare the performance of our model with other model, the statistics of particle velocity as well as concentration are investigated. Numerical simulation results show good agreement with available experimental data.

• Nuclear Engineering and Technology
• /
• v.55 no.12
• /
• pp.4395-4407
• /
• 2023

Bubble columns are widely encountered in several industries, especially in the field of nuclear safety. The Eulerian-Eulerian and the Eulerian-Lagrangian methods are commonly used to investigate bubble columns. Eulerian approaches require additional tasks such as strict volume conservation at the interface and a predefined well-structured grid. In contrast, the Lagrangian approach can be easily implemented. Hence, we introduce a fully Lagrangian approach for the simulation of bubble columns using the discrete bubble model (DBM) and moving particle semi-implicit (MPS) methods. Additionally, we propose a rigorous method to estimate the volume fraction accurately, and verified it through experimental data and analytical results. The MPS method was compared with the experimental data of Dambreak. The DBM was verified by analyzing the terminal velocity of a single bubble for each bubble size. It agreed with the analytical results for each of the four drag correlations. Additionally, the improved method for calculating the volume fraction showed agreement with the Ergun equation for the pressure drop in a packed bed. The implemented MPS-DBM was used to simulate the bubble column, and the results were compared with the experimental results. We demonstrated that the MPS-DBM was in quantitative agreement with the experimental data.

• Journal of Korean Society for Atmospheric Environment
• /
• v.33 no.1
• /
• pp.45-53
• /
• 2017

A high resolution model is proposed for calculating the temperature field of a large city, based upon a Lagrangian particle model. Utilizing the analogy between the heat and mass transport phenomena in turbulent flows, a Lagrangian particle model, originally developed for air pollutant dispersion problems, is adapted for simulating heat transport. In the model conceptual heat particles are released into the atmosphere from the heat sources and move along with the turbulent winds in accordance with the Markov process. The potential temperature assumed to be conserved along with heat particles serves as a tag, so the temperature fields can be deduced from the distribution of particles. The wind fields are constructed from a diagnostic meteorology model incorporating a morphological model designed for building flows. Test run shows the robustness of the modeling system.

• Journal of Korean Society for Atmospheric Environment
• /
• v.33 no.6
• /
• pp.583-592
• /
• 2017

A method is proposed for locating the heat sources from temperature observations, and its applicability is investigated for urban thermal environment simulations. A Lagrangian particle dispersion model, which is originally built for simulating the pollutants spread in the air, is exploited to identify the heat sources by transporting the Lagrangian heat particles backwards in time. The urban wind fields are estimated using a diagnostic meteorological model incorporating the morphological model for the urban canopy. The proposed method is tested for the horizontally homogeneous urban boundary layer problems. The effects of the turbulence levels and the computational time on the simulation are investigated.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.1
• /
• pp.23-30
• /
• 2004

In the Lagrangian vortex particle method based on the vorticity-velocity formulation for solving the incompressible Navier-Stokes equations, a numerical scheme for calculating pressure fields is presented. Implementation of the numerical method is directly connected with the well-established surface panel methods, just by dealing with the dynamic coupling among vorticity field. Assuming the vorticity and the velocity fields are to be calculated in time domain analysis, the pressure calculation for a complete set of solution at present time step is performed in a similar way to the one used in the Eulerian description. For a validation of the present method, we illustrate the early development of the viscous flow about an impulsive started circular cylinder for Reynolds number 550. The comparative study with the Eulerian finite Volume method provides an extensive understanding and application of the mesh-free Lagrangian vortex methods for numerical simulation of viscous flows around arbitrary bodies of general shape.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.241-251
• /
• 1991

The present simulation model relies on a new approach of the heavy particle motion in a turbulent flow considering the time and space correlation to the Lagrangian point of view. The turbulent field is, here, assumed that its characteristic scales are random and follow a Poisson's distribution. Using this model, we have computed the trajectory of each particle, that is, its velocity and position at each time in order to study the dispersion of particles in a grid turbulent flow. The computed results have been compared to the corresponding experimental data. Due to the complex mechanism of turbulence and the theoretically and experimentally lacking information, we had to make some assumptions for simplifying the situation, but we have found the good agreement between simulated and measured results. In particular, the application of the present method on the Lagrangian correlation of particle provides an interesting alternative to the usual computational methods.

• 한국전산유체공학회:학술대회논문집
• /
• 2002.10a
• /
• pp.41-46
• /
• 2002

A numerical simulation was made to determine the motion of particles in the fluid. The simulation is based on the Eulerian-Lagrangian method. The fluid motion was solved using a PISO-based finite-element method and a $\kappa-\epsilon$ model of turbulence. In the Lagrangian method for the solid phase, the trajectories of particles are calculated by integrating the equations of motion of a single Particle, and the collision between particles are taken into account. The influence of particles on the fluid phase is taken into account by introducing source terms in the Eulerian equations govering the fluid flow. It is known as the particle-source-in-cell (PSIC) method. Also, the turbulent effect in the particles and fluid notion is considered. The numerical results were compared with the experiment for a two-phase flow in a vertical pipe.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.7
• /
• pp.944-951
• /
• 2001

The purpose of this study is to investigate the effect of shear on turbulent diffusion. Turbulent Couette flows at low Reynolds number are numerically simulated using a Lagrangian PDF method. Flow field and particle trajectories are computed and analyzed in detail. Statistics for particle dispersion obtained from numerical simulations is compared with the classical scaling relations for dispersion in a shear flow.