• Proceedings of the KSME Conference
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• 2003.11a
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• pp.816-821
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• 2003

The pumping characteristics of a disk-type drag pump (DTDP) from free molecular flow region to the slip flow region are calculated by the direct simulation Monte Carlo (DSMC) method. In this study, the pumping performance is studied numerically for several channel depths. The interaction between molecules is modeled by variable hard-sphere (VHS). The no time counter method is used as a collision sampling technique. The clearance between rotor and stator is considered an effect on performance. Spiral channels are cut on both upper and lower sides of rotating disks, and stationary disks are planar. A three-dimensional DSMC method for the analysis of steady rarefied flows in a single-stage DTDP has been developed. Velocity and density fields were obtained by the DSMC simulation in the rotor. The present experimental data in the outlet pressure range of $7.5{\times}10^{-3}{\sim}4$ Torr were compared with the DSMC results in the single-stage DTDP. Comparison between the experimental data and DSMC results showed good agreement.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.11-19
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• 2005

First, methods of numerical analysis of gas-particle flows is classified into micro, meso and macro scale approaches based on the concept of multi-scale mechanics. Next, the explanation moves on to discrete particle simulation where motion of individual particles is calculated numerically using the Newtonian equations of motion. The author focuses on the cases where particle-to-particle interaction has significant effects on the phenomena. Concerning the particle-to-particle interaction, two cases are considered: the one is collision-dominated flows and the other is the contact-dominated flows. To treat this interaction mathematically, techniques named DEM(Distinct Element Method) or DSMC (Direct Simulation Monte Carlo) have been developed DEM, which has been developed in the field of soil mechanics, is useful for the contact -dominated flows and DSMC method, developed in molecular gas flows, is for the collision-dominated flows. Combining DEM or DSMC with CFD (computer fluid dynamics), the discrete particle simulation becomes a more practical tool for industrial flows because not only the particle-particle interaction but particle-fluid interaction can be handled. As examples of simulations, various results are shown, such as hopper flows, particle segregation phenomena, particle mixing in a rotating drum, dense phase pneumatic conveying, spouted bed, dense phase fluidized bed, fast circulating fluidized bed and so on.

• Journal of Aerospace System Engineering
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• v.12 no.5
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• pp.8-15
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• 2018

The geostationary satellite uses a liquid apogee engine, to obtain a required velocity increment to enter a geostationary orbit. However, as the liquid apogee engine operates in the vacuum, a considerable disbursement of exhaust plume flow, from the liquid apogee engine can trigger a backflow. As this backflow may possibly collide with the satellite directly, it can cause adverse effects such as surface contamination, thermal load, and altitude disturbance, that can generate performance reduction of the geostationary satellite. So, this study investigated exhaust plume behavior of 400 N grade liquid apogee engine numerically. To analyze exhaust plume behavior in vacuum condition, the DSMC (Direct Simulation Monte Carlo) method based on Boltzmann equation is used. As a result, thermal fluid characteristics of exhaust plume such as temperature and number density, are observed.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.1-11
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• 2021

To develop technologies for the stable operation of electric propulsion systems, the exhaust plume behavior of electric thrusters was studied using PIC-DSMC(particle-in-cell and direct simulation Monte Carlo). For the numerical analysis, the Simple Electron Fluid Model using Boltzmann relation was employed, and the charge and momentum exchanges due to atom-ion collisions were considered. The results of this study agreed with the plasma potentials measured experimentally. Near the thruster exit, active collisions among particles and charge exchanges created slow ions and fast atoms, which were expected to significantly affect the trajectory and velocity of the thruster exhaust plume.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.12
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• pp.1501-1510
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• 2004

The pumping characteristics of a single-stage disk-type drag pump (DTDP) are calculated for the variation of the vertical clearance between a rotor and stator by the three-dimensional direct simulation Monte Carlo (DSMC) method. The gas flow mainly belongs to the molecular transition flow region. Spiral channels of a DTDP are cut on the both the upper and lower sides of a rotating disk, but a stationary disk is planar. The interaction between molecules is described by the variable hard-sphere model. The no time counter method is used as a collision sampling technique. The vertical clearance has a significant effect on the pumping performance. Experiments are performed under the outlet pressure range of 0.4∼533 Pa. When the numerical results are compared with the experimental data, the numerical results agree well quantitatively

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.10
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• pp.1406-1418
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• 2002

The direct simulation Monte Carlo(DSMC) method is employed to calculate the etch rate on Al wafer. The etchant is assumed to be Cl$_2$. The etching process of an Al wafer in a helicon plasma etcher is examined by simulating molecular collisions of reactant and product. The flow field inside a plasma etch reactor is also simulated by the DSMC method fur a chlorine feed gas flow. The surface reaction on the Al wafer is simply modelled by one-step reaction: 3C1$_2$+2Allongrightarrow1 2AIC1$_3$. The gas flow inside the reactor is compared for six different nozzle locations. It is found that the flow field inside the reactor is affected by the nozzle locations. The Cl$_2$ number density on the wafer decreases as the nozzle location moves toward the side of the reactor. Also, the present numerical results show that the nozzle location 1, which is at the top of the reactor chamber, produces a higher etch rate.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.142-149
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• 1996

이차원 노즐을 통하여 저밀도 환경으로 팽창하는 희박류의 분석에 있어서 불연속좌표법과 결합된 유한차분법(finite-difference method coupled with the discrete-ordinate method, FDDO)과 직접모사법(direct-simulation Monte-Carlo method, DSMC)이 비교되었다. FDDO를 이용한 분석에서는 충돌적분모델을 도입하여 간단해진 볼츠만식(Boltzmann equation)이 불연속좌표법을 이용하여 물리적 공간에서는 연속이나 분자속도 공간에서는 불연속좌표로 표시되는 편미분방정식군으로 변환되어 유한차분법에의하여 수치해석 되었다. 직접모사법에서는 분자모델로 가변강구모델(variable hard sphere model, VHS)이, 충돌샘플링모델로는 비시계수법(no time counter method, NTC)이 채택되었다. 전혀 다른 두 가지 방법에 의한 노즐 내부에서의 유체흐름 해석결과는 매우 잘 일치하였으며, 노즐 외부의 plume 영역에서는 FDDO에 의한 해석결과가 직접모사법에 의한 해석결과에 비하여 약간 느린 팽창을 보였다.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.347-359
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• 2015

A method of describing the rovibrational energy transitions and coupled chemical reactions in the direct simulation Monte Carlo (DSMC) calculations is constructed for $H(^2S)+H_2(X^1{\Sigma}_g)$ and $He(^1S)+H_2(X^1{\Sigma}_g)$. First, the state-specific total cross sections for each rovibrational states are proposed to describe the state-resolved elastic collisions. The state-resolved method is constructed to describe the rotational-vibrational-translational (RVT) energy transitions and coupled chemical reactions by these state-specific total cross sections and the rovibrational state-to-state transition cross sections of bound-bound and bound-free transitions. The RVT energy transitions and coupled chemical reactions are calculated by the state-resolved method in various heat bath conditions without relying on a macroscopic properties and phenomenological models of the DSMC. In nonequilibrium heat bath calculations, the state-resolved method are validated with those of the master equation calculations and the existing shock-tube experimental data. In bound-free transitions, the parameters of the existing chemical reaction models of the DSMC are proposed through the calibrations in the thermochemical nonequilibrium conditions. When the bound-free transition component of the state-resolved method is replaced by the existing chemical reaction models, the same agreement can be obtained except total collision energy model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.3
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• pp.169-176
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• 2019

In the present study, a CFD/DSMC hybrid method performed by a coupled analysis between the CFD method and the DSMC method was developed to obtain the flow information on the rarefied gas flows effectively. Flow simulations around the high speed vehicles on the transition flow regimes were conducted by using the developed method. The FRESH-FX vehicle made of cone and cylinder shapes was considered for the simulations. The results of the hybrid method were compared with the results of the pure CFD and the pure DSMC method to confirm the reliability and efficiency of the hybrid method. It was found that the gradient and the intensity of the shock waves were weakened due to the relatively low density on the transition flow regime. It was confirmed that the results of the hybrid analysis were different to those of the pure CFD analysis and almost identical to those of the pure DSMC analysis. In addition, the computational time of the hybrid method was reduced than that of the pure DSMC method. As a result, it was obtained that the validity and the efficiency of the CFD/DSMC hybrid method.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.2
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• pp.8-18
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• 2001

The direct simulation Monte Carlo Method is applied to investigate the two-dimensional flow fields of a turbomolecular pump(TMP) in both molecular and transition flow regions. The pumping characteristics of the TMP are investigated for a wide range of the Knudsen number. The maximum of compression ratio and of pumping speed strongly depend on the Knudsen number in transition region, while they weakly depend on the Knudsen number in free molecular flow region. The present numerical results show good agreement with the previously known experimental data. Finally. the results of the single blade row in both molecular and transition regions are used to predict the overall performance of a TMP, which has three kinds of blade with 24-rows.