• 제목/요약/키워드: knudsen number

검색결과 61건 처리시간 0.021초

공기윤활 범프 저어널 베어링의 부상 특성에 관한 연구 (A Study on the Lift-off Characteristics of an Air-lubricated Bump Foil Journal Rearing)

  • 이용복;김창호;이남수;최동훈
    • Tribology and Lubricants
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    • 제17권6호
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    • pp.441-446
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    • 2001
  • In this paper the effect of bump compliance, load, and the number of pad on the lift-off speed is studied. When the load is greater and bump compliance lower, the shaft is lifted off at higher rotating speed. And when the load is applied near the center of pad, lift-off speed is lower. When the number of pad increases, the lift-off speed is higher. The lift-off characteristics can be used to lengthen the lift time of the coating and design the rotating machinery supported by bump bearings.

저궤도 재진입 비행체의 공력해석 (AERODYNAMIC ANALYSIS OF SUB-ORBITAL RE-ENTRY VEHICLE)

  • 김철완;이융교;이대성
    • 한국전산유체공학회지
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    • 제13권2호
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    • pp.1-7
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    • 2008
  • For Aerodynamic analysis of vehicle at altitude, 100km, the validity of governing equations based on continuum model, was reviewed. Also, as the preliminary study for the sub-orbital space plane development, a candidate geometry was suggested and computational fluid dynamic(CFD) analysis was performed for various angles of attack in subsonic and supersonic flow regimes to analyze the aerodynamic characteristics and performance. The inviscid flow analyses showed that the stall starts at angle of attack above $20^{\circ}$, the maximum drag is generated at angle of attack, $87^{\circ}$ and the maximum lift to drag ratio is about 8 in subsonic flow. In supersonic, the stall angle is about $40^{\circ}$ and the maximum drag is generated at angle of attack, $90^{\circ}$. Also, mach number distribution of re-entry vehicle was computed versus altitudes.

Numerical Prediction of the Flow Characteristics of a Micro Shock Tube

  • ;;김희동
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2011년도 제37회 추계학술대회논문집
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    • pp.178-181
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    • 2011
  • Recently, micro shock tube is being extensively used in various fields of engineering applications. The flow characteristics occurring in the micro shock tube may be significantly different from that of conventional macro shock tube due to very low Reynolds number and Knudsen number effects which are, in general, manifested in such flows of rarefied gas, solid-gas two-phase, etc. In these situations, Navier-Stokes equations cannot properly predict the micro shock tube flow. In the present study, a two-dimensional CFD method has been applied to simulate the micro shock tube, with slip velocity and temperature jump boundary conditions. The effects of wall thermal conditions on the unsteady flow in the micro shock tube were also investigated. The unsteady behaviors of shock wave and contact discontinuity were, in detail, analyzed. The results obtained show much more attenuation of shock wave, compared with macro-shock tubes.

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HALL EFFECTS ON HYDROMAGNETIC NATURAL CONVECTION FLOW IN A VERTICAL MICRO-POROUS-CHANNEL WITH INJECTION/SUCTION

  • BHASKAR, P.;VENKATESWARLU, M.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • 제24권1호
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    • pp.103-119
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    • 2020
  • In this work, the hydromagnetic and thermal characteristics of natural convection flow in a vertical parallel plate micro-porous-channel with suction/injection is analytically studied in the presence of Hall current by taking the temperature jump and the velocity slip at the wall into account. The governing equations, exhibiting the physics of the flow formation are displayed and the exact analytical solutions have been obtained for momentum and energy equations under relevant boundary conditions. The impact of distinct admissible parameters such as Hartmann number, Hall current parameter, permeability parameter, suction/injection parameter, fluid wall interaction parameter, Knudsen number and wall-ambient temperature ratio on the flow formation is discussed with the aid of line graphs. In particular, as rarefaction parameter on the micro-porous-channel surfaces increases, the fluid velocity increases and the volume flow rate decreases for injection/suction.

Numerical Simulation of the Effect of Finite Diaphragm Rupture Process on Micro Shock Tube Flows

  • ;김희동
    • 한국추진공학회:학술대회논문집
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    • 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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    • pp.309-317
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    • 2012
  • Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.

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The Static and Dynamic Performance of a MEMS/MST Based Gas-Lubricated proceeding Bearing with the Slip Flow Effect

  • Kwak, H.-D.;Lee, Y.-B.;Kim, C.-H.;Lee, N.-S.;Choi, D.-H.
    • 한국윤활학회:학술대회논문집
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    • 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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    • pp.103-104
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    • 2002
  • The influence of the slip flow on the MEMS/MST based gas-lubricated proceeding bearing is investigated. Based on the modified Reynolds equation, the numerical analysis of the finite difference method was developed by applying the first order slip flow approximation. The numerical prediction of bearing performance provides the significant results concerning the slip flow effect in micro scale gas-lubricated proceeding bearing. The result indicates that the load-carrying capacity as well as the rotordynamic coefficients were significantly reduced due to the slip flow. Through this work, it is concluded that the slip flow effect could not be ignored in the micro gas-lubricated proceeding bearing.

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원판형 드래그펌프의 성능특성에 관한 연구 (A Study on the Performance Characteristics of a Disk-type Drag Pump)

  • 황영규;허중식
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집E
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    • pp.643-648
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    • 2001
  • The direct simulation Monte Carlo(DSMC) method is applied to investigate steady and unsteady flow fields of a single-stage disk-type drag pump. Two different kinds of pumps are considered: the first one is a rotor-rotor combination, and the second one is a rotor-stator combination. The pumping channels are cut on a rotor and stator. The rotor and stator have 10 Archimedes' spiral blades, respectively. In the present DSMC method, the variable hard sphere model is used as a molecular model, and the no time counter method is employed as a collision sampling technique. For simulation of diatomic gas flows, the Borgnakke-Larsen phenomenological model is adopted to redistribute the translational and internal energies. The DSMC results are in good agreement with the experimental data.

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미끄럼 영역에 있는 나노입자 프랙탈 응집체의 전기이동도 거동 특성 (Electrical Mobility Behavior of Nanoparticle Fractal Agglomerates in the Slip Regime)

  • 신원규
    • 한국대기환경학회지
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    • 제29권2호
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    • pp.211-216
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    • 2013
  • For diffusion limited cluster agglomerates the ratio of the mobility radius to the radius of gyration $R_m/R_g$ vs. N and the ratio of the mobility radius to the radius of primary particle $R_m$/a are determined using experimental data obtained with DMA-APM and tandem DMA over a range of Knudsen numbers extending into the transition region where there is a lack of data. It was found that in slip regime with the number of primary particles between 100 and 400, datapoints are found to be between the two asymptotic lines for the continuum and free molecular regimes as those datapoints are plotted in both $R_m/R_g$ vs. N and $R_m$/a vs. N.

Slip flow 영역에서의 미소채널 내 열전달 및 유동에 관한 수치적 연구 (A Numerical Study of Heat transfer and Flow Analysis for a Micro-channel in The Slip Flow Regime)

  • 정수인;김귀순;강범수
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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    • pp.391-394
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    • 2006
  • In this paper, the thermal lattice Boltzmann method(TLBM) proposed by Guo et al.(2002) is applied to analyze the forced convective flow and heat transfer of 2-D micro channel. Nonequilibrium extrapolation boundary condition is adopted to simulate the velocity and temperature behavior at wall boundaries. Numerical results obtained by the present study give a good prediction of the micro fluidic characteristics with thermal effects.

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마이크로채널 흐름에 관한 종횡비의 영향 (Effect of Aspect Ratio on Gas Microchannel Flow)

  • 타줄 이슬람;이연원
    • 동력기계공학회지
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    • 제11권3호
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    • pp.16-21
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    • 2007
  • Three dimensional numerical study was carried out to investigate the effect of aspect ratio on microchannel flow. We considered five straight rectangular channels with aspect ratios (height/width) 0.2, 0.4, 0.6, 0.8 and 1.0. Nitrogen gas flow was investigated for both slip and noslip wall boundary conditions. Isothermal wall condition was assumed. We used control volume method for this simulation. The slip velocity increases with the increase of aspect ratio. Friction coefficient decreases with the increase of aspect ratio. Slip friction coefficient is lower than noslip friction coefficient. Mass flow rate of slip model is higher than that of noslip model. We compared our results with the experimental result reported in the literature. The agreement was good.

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