• 제목/요약/키워드: Boundary Layer dynamics

검색결과 144건 처리시간 0.033초

기액계면의 경계층 두께에 관한 연구 (A Study on the Boundary Layer Thickness at a Liquid-Vapor Interface)

  • 최순호;송치성;최현규;이정혜;김경근
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 추계학술대회
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    • pp.1086-1091
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    • 2004
  • The boundary layer is a very important characteristic of a liquid-vapor interface since it governs the heat and mass transfer phenomena across an interface. However, the thickness of a boundary layer is generally micro- or nano-sized, which requires highly accurate measurement devices and, consequently, costs the related experiments very high and time-consuming. Due to these size dependent limitations, the experiments related with a nano-scaled size have suffered from the errors and the reliability of the obtained data. This study is performed to grasp the characteristics of a liquid-vapor interface, by using a molecular dynamics method. The simulation results were compared with other studies if possible. Although other studies reported that there existed a temperature discontinuity over an interface when the system was reduced to micro- or nano-sized, we confirmed that there was no such a temperature discontinuity.

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PUSHCHINO DYNAMICS OF INTERNAL LAYER

  • Yum, Sang Sup
    • Korean Journal of Mathematics
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    • 제12권1호
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    • pp.7-14
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    • 2004
  • The existence of solutions and the occurence of a Hopf bifurcation for the free boundary problem with Pushchino dynamics was shown in [3]. In this paper we shall show a Hopf bifurcation occurs for the free boundary which is given by (1).

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다공도 및 팽창파의 영향을 고려한 BLEED 경계조건 수치 모델링의 정확도 향상 연구 (ACCURACY IMPROVEMENT OF THE BLEED BOUNDARY CONDITION WITH THE EFFECTS OF POROSITY VARIATIONS AND EXPANSION WAVES)

  • 김광현;최요한;김종암
    • 한국전산유체공학회지
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    • 제21권1호
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    • pp.94-102
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    • 2016
  • The present paper deals with accuracy improvement of a bleed boundary condition model used to improve the performance of supersonic inlets. In order to accurately predict the amount of bleed mass flow rates, this study performs a scaling of sonic flow coefficient data for 90-degree bleed holes in consideration of Prandtl-Meyer expansion theory. Furthermore, it is assumed that porosity varies with stream-wise location of the porous bleed plate to accurately predict downstream boundary layer profiles. The bleed boundary condition model is demonstrated through Computational Fluid Dynamics(CFD) simulations of bleed flows on a flat plate with/without an oblique shock. As a result, the bleed model shows the improved accuracy of bleed mass rates and downstream boundary layer profiles.

충격파 경계층 상호작용에서 난류모델 및 난류점성의 효과 (EFFECTS OF TURBULENCE MODEL AND EDDY VISCOSITY IN SHOCK-WAVE / BOUNDARY LAYER INTERACTION)

  • 전상언;박수형;변영환
    • 한국전산유체공학회지
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    • 제18권2호
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    • pp.56-65
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    • 2013
  • Two compression ramp problems and an impinging shock problem are computed to investigate influence of turbulence models and eddy viscosity on the shock-wave / boundary layer interaction. A Navier-Stokes boundary layer generation code was applied to the generation of inflow boundary conditions. Computational results are validated well with the experimental data and effects of turbulence models are investigated. It is shown that the behavior of turbulence (eddy) viscosity directly affects both the extent of the separation and shock-wave positions over the separation.

원반형 경계층 펌프의 전산 설계 (Computational Design of a Disk-Shape Boundary-Layer Pump)

  • 정수윤;장세명;양재삼
    • 한국유체기계학회 논문집
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    • 제13권2호
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    • pp.12-17
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    • 2010
  • A kind of disk-shape boundary layer pump is designed numerically by using a software of computational fluid dynamics, which is widely used for the special purposes such as artificial hearts, bio-fluidics and transportation of oceanic lives, etc. From the numerical simulation with an axisymmetric model, some benchmark problems are tested and compared with experimental results. The performance of disk pump is graphically visualized from the computational results, and converted to the dimensionless parameters. Finally, the obtained numerical data in the present investigation can be used for the baseline for new design to achieve a more efficient disk pump.

UCD 대기경계층 풍동을 이용한 경계층 형성 (Modeling of Boundary Layer using Atmospheric Boundary Layer Wind Tunnel of UCD)

  • 부루스 알 와이트;김봉환;김대성
    • 한국기계가공학회지
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    • 제11권2호
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    • pp.118-124
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    • 2012
  • The simulation of the air flow over models in atmospheric boundary layer wind tunnel is a research region based on advanced scientific technologies imposed by the necessity of studying the turbulent fluid dynamics in the proximity of the Earth's surface. In this study, the atmospheric boundary layer wind tunnel of UCD is used, the mean velocities are measured by augmentation devices such as roughness blocks and spires. The experimental results of mean velocity profile are well fitted with the value of power law.

Developments and applications of a modified wall function for boundary layer flow simulations

  • Zhang, Jian;Yang, Qingshan;Li, Q.S.
    • Wind and Structures
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    • 제17권4호
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    • pp.361-377
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    • 2013
  • Wall functions have been widely used in computational fluid dynamics (CFD) simulations and can save significant computational costs compared to other near-wall flow treatment strategies. However, most of the existing wall functions were based on the asymptotic characteristics of near-wall flow quantities, which are inapplicable in complex and non-equilibrium flows. A modified wall function is thus derived in this study based on flow over a plate at zero-pressure gradient, instead of on the basis of asymptotic formulations. Turbulent kinetic energy generation ($G_P$), dissipation rate (${\varepsilon}$) and shear stress (${\tau}_{\omega}$) are composed together as the near-wall expressions. Performances of the modified wall function combined with the nonlinear realizable k-${\varepsilon}$ turbulence model are investigated in homogeneous equilibrium atmosphere boundary layer (ABL) and flow around a 6 m cube. The computational results and associated comparisons to available full-scale measurements show a clear improvement over the standard wall function, especially in reproducing the boundary layer flow. It is demonstrated through the two case studies that the modified wall function is indeed adaptive and can yield accurate prediction results, in spite of its simplicity.

금강 하구의 해수순환역학 (CIRCULATION DYNAMICS OF THE KEUM RIVER ESTYARY)

  • 정종율;이재학;안희수
    • 한국해양학회지
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    • 제18권2호
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    • pp.142-148
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    • 1983
  • 錦江河口의 6個定點에서 大.小潮기에 Instantaneous profiling技法으로 同時 觀測한 鹽分値를 분석하여 鹽分境界層의 變化特性을 밝혔다. 錦江河口를 鹽分境界層의 變化特性으로 分流해 본 缺課 定常波型河口(standing wave type estuary)임이 再次確認(Chung, 1981)되었으며 變化의 크기는 上流로 갈수록 커짐도 아울러 밝혀 졌다. 또한 鹽分境界層의 變化는 大潮期 보다 小潮期에 큼도 밝혀 졌다. 鹽分境界層(S<10%)의 持續時間은 小潮期에 越等히 긴데, Shinri-Saugke斷面 보다 上流域에서는 6時間以上 持續되고 Sochgot-Kupo斷面 사이에서는 0-3時間童 顔 持續됨이 밝혀 졌다. 따라서 錦江河口에서의 堆積作用은 持續時間의 分布特性에 따른 區域別의 Flocculation作用의 强弱에 의해 支配되고 있음도 아울러 밝혀 졌다.

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