• 대한기계학회논문집B
• /
• 제41권4호
• /
• pp.239-248
• /
• 2017

원형 실린더 주위의 유동에 부유된 입자가 실린더 근처에서 분산되거나 실린더에 부착되는 특성을 이해하는 것이 중요하다. 본 연구에서는 입자의 부착을 조절하는 방안으로 실린더의 회전을 고려해 보았고, 실린더의 회전 속도 및 입자의 Stokes 수가 실린더 주위의 유동과 입자의 분산 및 부착 특성에 미치는 영향을 수치해석적으로 연구하였다. 해석 결과 4보다 작은 Stokes 수에서는 회전속도가 증가함에 따라 부착효율이 크게 감소하였고, 4보다 큰 Stokes 수에서는 회전속도가 증가함에 따라 부착효율이 다소 증가하였다. 한편, 회전속도가 일정한 경우에는 Stokes 수가 증가함에 따라 입자의 부착효율이 증가하고, 입자의 부착 위치도 넓어졌다.

• 한국기계가공학회지
• /
• 제18권2호
• /
• pp.73-81
• /
• 2019

Numerical simulations are performed for the thermal fluid flow around a circular cylinder, and the particle trajectories are calculated to investigate the particle motions and deposition characteristics. We aim to understand the effects of three important parameters (particle Stokes number, temperature difference in the flow and on the cylinder surface, and thermal conductivity ratio between the fluid and the particles) on the deposition efficiency. The results show that the thermophorectic effect is insignificant for particles with large Stokes numbers, but it affects particles with small Stokes numbers. The deposition efficiency increases with the increase in temperature difference between the flow and the cylinder or the decrease in ratio of thermal conductivity of the particles to the fluid. When thermophoresis becomes significant, the particles are deposited even on the back side of the cylinder.

• 대한기계학회논문집B
• /
• 제31권1호
• /
• pp.29-39
• /
• 2007

A second-moment closure is applied to the prediction of a homogeneous turbulent shear flow laden with mono-size particles. The closure is curried out based on a 'two-fluid' methodology in which both carrier and dispersed phases are considered in the Eulerian frame. To reduce the number of coupled differential equations to be solved, Reynolds stress transport equations and algebraic stress models are judiciously combined to obtain the Reynolds stress of carrier and dispersed phases in the mean momentum equation. That is, the Reynolds stress components for carrier and dispersed phases are solved by modelled transport equations, but the fluid-particle velocity covariance tensors are treated by the algebraic models. The present predictions for all the components of Reynolds stresses are compared to the DNS data. Reasonable agreements are observed in all the components, and the effects of the coupling of carrier and dispersed phases are properly captured in every aspects.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
• /
• pp.9-11
• /
• 2003

A homogeneous flow field including more than 2000 spherical particles was directly simulated. Particles are settling by gravity with the Reynolds number ranging from 50 to 300, based on diameter and slip velocity. Particular attention was focused on the distribution of particles. The Reynolds-number dependence, influences of particle rotation and loading ratio, and the dynamics of particle clusters are discussed. In the higher Reynolds number case, the wake attraction causes particle clusters and the average drag coefficient decreases significantly. Non-rotating particles maintain cluster structure and rotating ones moves randomly in the horizontal direction. It is because of the difference in the direction of the lift force.

• 대한기계학회논문집
• /
• 제19권9호
• /
• pp.2342-2352
• /
• 1995

Deposition of flame-synthesized silica particles onto a target is utilized in optical fiber preform fabrication processes. The particles are convected and deposited onto the target. Falkner-Skan wedge flow was chosen as the particle laden flow. Typically the particles are polydisperse in size and follow a lognormal size distribution. Brownian diffusion, thermophoresis, and coagulation of the particles were considered and effects of these phenomena on particle deposition were studied. A moment model was developed in order to predict the particle number density and the particle size distribution simultaneously. Particle deposition with various wedge configurations was examined for conditions selected for a typical VAD process. When coagulation was considered, mean particle size and its standard deviation increased and particle number density decreased, compared to the case without coagulation. These results proved the fact that coagulation effect expands particle size distribution. The results were discussed with characteristics of thermal and diffusion boundary layers. As the boundary layers grow in thickness, overall temperature and concentration gradients decrease, resulting in decrease of deposition rate and increase of particle residence time in the flow and thus coagulation effect.

• 대한기계학회논문집B
• /
• 제22권11호
• /
• pp.1499-1508
• /
• 1998

A numerical study is performed to investigate pressure drops, particle trajectories and erosion around orifice plates in pulverized coal pipe lines. Particle impaction rates change significantly with orifice shapes and Stokes numbers. At Reynolds number of $5{\times}10^5$, the pulverized coal flows well with streamlines and do not collide at the orifice plates at small sizes (${\sim}20{\mu}m$). However, the large particles (over $70{\mu}m$) impact on the front face of the orifice and erode the orifice surface. The pressure loss coefficients around the erode orifice are largely different from the designed original orifice.

• 한국입자에어로졸학회지
• /
• 제13권4호
• /
• pp.173-182
• /
• 2017

An Eulerian-Lagrangin approach is used to compute particle dispersion from a power plant chimney. For air flow, three-dimensional incompressible filtered Navier-Stokes equations are solved with a subgrid-scale model by integrating the Newton's equation, while the dispersed phase is solved in a Lagrangian framework. The velocity ratios between crossflow and a jet of 0.455 and 0.727 are considered. Flow fields and particle distribution of both cases are evaluated and compared. When the velocity ratio is 0.455, it demonstrates a Kelvin-Helmholtz vortex structure above the chimney caused by the interaction between crossflow and a jet, whereas the other case shows flow structures at the top of the chimney collapsed by fast crossflow. Also, complex wake structures cause different particle distributions behind the chimney. The case with the velocity ratio of 0.727 demonstrates strong particle concentration at the vortical region, whereas the case with the velocity ratio of 0.455 shows more dispersive particle distribution. The simulation result shows similar tendency to the experimental result.

• 대한기계학회논문집B
• /
• 제30권11호
• /
• pp.1101-1106
• /
• 2006

To investigate a relation between fine scale eddies and particle dispersion in a near-wall turbulence, direct numerical simulations of turbulent channel flow laden particle are performed for $Re_{\tau}$=180. The motions of 0,8 million particles are calculated for several particle response times ($t_p$) which is the particle response time based on stokes’ friction law. The number density of particles has a tendency to increase with approaching the near-wall regions ($y^+$<20) except for cases of very small and large particle response times (i.e. $t_p$=0.02 and 15). Near the wall, the behavior and distribution of particles are deeply associated with the fine scale eddies, and are dependent on particle response times and a distance from the wall. The Stokes number that causes preferential distribution in turbulence is changed by a distance from the wall. The influential Stokes number based on the Burgers' vortex model is derived by using the time scale of the fine scale eddies. The influential Stokes number is also dependent on a distance from the wall and shows large value in the buffer layer.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
• /
• pp.301-308
• /
• 1999

The present study investigates numerically particle laden flow through compressor cascades and a rocket nozzle. Engines are affected by various particles which are suspending in the atmosphere. Especially in the case of aircraft aviating in volcanic, industrial and desert region including many particles, each components of engine system are damaged severely. That damage modes are erosion of compressor blading and rotor path components, partial or total blockage of cooling passage and engine control system degradation. Numerical prediction and experimental data, erosion rates are predicted for two materials - ceramic, soft metal - on compressor blade surface. Aluminum oxide ($Al_2O_3$) Particles included in solid rocket propelant make ablative the rocket motor nozzle and imped the expansion processes of propulsion. By the definition of particle deposition efficiency, characteristics of particles impaction are considered quantitatively Stoke number is defined over the various particle sizes and particle trajectories are treated by Lagrangian approach. Particle stability is considered by definition of Weber number in rocket nozzle and particle breakup and evaporation is simulated in a rocket nozzle.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.3197-3202
• /
• 2007

An analysis program for pedestrian flow has been developed to investigate the flow patterns of passenger in railway stations. Analysis algorithms for pedestrian flow based on DEM(Discrete Element Method) are newly developed. There are lots of similarity between particle-laden two phase flow and passenger flow. The velocity component of 1st phase corresponds to the unit vector of calculation cell, each particle to passenger, volume fraction to population density and the particle velocity to the walking velocity, etc. And, the walking velocity of passenger is also represented by the function of population density. Key algorithms are developed to determine the position of passenger, population density and numbering to each passenger. By using the developed program, we compared the simulation results of the effects of the location and size of exit and elapsed time.