• Title/Summary/Keyword: 층류경계층

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Aeroacoustic Noise Generation in Unsteady Laminar Boundary-layer Separation (비정상 층류 경계층 박리에 의한 유동 소음)

  • Choi, Hyo-Won;Moon, Young-J.
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.300-305
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    • 2001
  • The unsteady flow structure and the related noise generation, which are caused by the separation of a two-dimensional, incompressible, laminar boundary-layer on the flat plate under the influence of local adverse pressure gradient, are numerically examined. The characteristic lines of the wall pressure are examined to understand the unsteady behavior of vortex shedding near the reattachment point of the separation bubble. Also, the generation and propagation of the vortex-induced noise in the separated boundary-layer are calculated by the method of computational aero-acoustics (CAA), and the effects of Reynolds number, Mach number and the strength of the adverse pressure gradient on the unsteady flow and noise characteristics are examined.

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Visualization Study on the Boundary Layer and Near-Wake of a Stationary Airfoil at Low Reynolds Numbers (저 레이놀즈수에서 정지된 에어포일의 경계층 및 근접 후류 가시화 연구)

  • Yang, Jae-Hun;Chang, Jo-Won
    • Journal of the Korean Society of Visualization
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    • v.4 no.2
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    • pp.44-50
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    • 2006
  • A visualization study on the boundary layer and near-wake of an NACA 0012 airfoil was con-ducted in order to investigate the influence of boundary layer behavior on the near-wake at low Reynolds numbers. The present study is investigated at static angles of attack ${\alpha}=0^{\circ},\;3^{\circ},\;6^{\circ}$ and $Re=2.3{\times}10^4,\;3.3{\times}10^4,\;4.8{\times}10^4$ by using a smoke-wire technique. The results of this study show that the laminar boundary layer on the airfoil surface is attached to the surface at ${\alpha}=0^{\circ}$, and that laminar separation of boundary layer on the airfoil surface occurs at ${\alpha}=3^{\circ}$. Furthermore, reattachment of the boundary layer occurs in the case of ${\alpha}=6^{\circ}$. In the current study, the location of the laminar separation point moves upstream as the Reynolds number and the angle of attack increase.

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Influence of Boundary Layer Behavior on the Near-Wake of an NACA 0012 Airfoil (NACA 0012 에어포일의 경계층 거동이 근접 후류에 미치는 영향)

  • Yang, Jae-Hun;Kim, Dong-Ha;Chang, Jo-Won
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.14 no.4
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    • pp.24-30
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    • 2006
  • An experimental study was carried out in order to investigate the influence of boundary layer behavior on the near-wake at low Reynolds numbers. An X-type hot-film probe(55R51) was used to measure the near-wake of an NACA 0012 airfoil at static angles of attack ${\alpha}=0^{\circ}$, $3^{\circ}$, and $6^{\circ}$, and the Reynolds numbers Re=2.3${\times}10^4$, 3.3${\times}10^4$, and 4.8${\times}10^4$. The results of the study show that the characteristics of the boundary layer on the airfoil surface have a close relationship with the mean velocity and turbulence intensity profiles of a near-wake. Therefore, the development of the boundary layer, the position of the separation point, and the existence and non-existence of reattachment on the airfoil surface were represented by the differences in mean velocity and turbulence intensity profiles of the near-wake.

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A Study on the Thermal Boundary Layer Flow of a Micropolar Fluid in the Vicinity of a Wedge (미세극성 유체 유동장에 놓여진 쐐기형 물체주위의 열경계층에 관한 연구)

  • 김윤제
    • The Korean Journal of Rheology
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    • v.11 no.2
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    • pp.122-127
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    • 1999
  • The characteristics of thermal boundary layer flow of a micropolar fluid in the vicinity of a wedge has been studied with constant surface temperature. The similarity variables found by Falkner and Skan are employed to reduce the streamwise-dependence in the coupled nonlinear boundary layer equations. Numerical solutions are presented for the heat transfer characteristics with Pr=1 using the fourth-order Runge-Kutta method and their dependence on the material parameters is discussed. The distributions of dimensionless temperature and Nusselt number across the boundary layer are compared with the corresponding flow problems for a Newtonian fluid over wedges. Numerical results show that for a constant wedge angle with a given Prandtl number, Pr=1, the effect of increasing values of K results in an increasing thermal boundary thickness for a micropolar fluid, as compared with a Newtonian fluid. For the case of the constant material parameter K, however, the heat transfer rate for a micropolar fluid is lower than that of a Newtonian fluid.

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Numerical Simulation of Vertical Wall Fires I. Turbulent Natural Convection Along Vertical Wall (수직벽화재의 수치 시뮬레이션 I. 수직벽 난류자연대류)

  • Park, Woe-Chul;Trouve, Arnaud
    • Fire Science and Engineering
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    • v.22 no.3
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    • pp.181-187
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    • 2008
  • Numerical simulation of natural convection along a vertical wall was carried out to evaluate the computational fluid dynamics simulator, which is to be utilized for study of vertical wall fires. The computed velocity and temperature profiles were compared with measurements over the turbulent boundary layer formed along the wall of 4m high and constant temperature. It fumed out that the simulator with default parameters failed to predict the turbulent natural convection showing the boundary layer flow laminar. The grid size $\Delta$x=5mm, ${\Delta}y={\Delta}z=10mm$ and Smagorinsky constant of the large eddy simulation $C_s$=0.1 were chosen through parametric investigations. Though turbulent mixing was not enough, the velocity distribution near wall, peak velocity, and temperature profile in the turbulent boundary layer agreed well with the measurements.

Experimental Study on Local Mass Transfer Characteristics of Flat Plate Using Tripping Wire (트리핑 와이어를 사용한 평판에서의 국소물질전달 특성에 관한 실험적 연구)

  • Yoo, Seong-Yeon;Cho, Woong-Sun;Jo, Woo-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.3
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    • pp.285-292
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    • 2013
  • The purpose of this research is to investigate how the boundary layer separation caused by a tripping wire installed in front of the flat plate affects the transition from laminar to turbulent flow, and consequently mass transfer. A naphthalene sublimation technique is used to measure the local mass transfer coefficients on the flat plate, and two boundary conditions for the developed and developing flow are considered to evaluate the effects of the flow boundary. The local mass transfer data for a flat plate with a tripping wire are compared with the data for a flat plate without a tripping wire. The variation trends of the local heat transfer coefficients for the plates with and without the tripping wire are similar to each other in the case of the developing flow, but are quite different for the developed flow. The average Sherwood number for the flat plate with a tripping wire is much higher than that without a tripping wire because of the boundary layer separation.

Shortcommings in Simulation of a Vertical Wall Fire by Using FDS (FDS를 사용한 수직벽화재 시뮬레이션의 문제점)

  • Park, Woe-Chul
    • Proceedings of the Korea Institute of Fire Science and Engineering Conference
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    • 2008.11a
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    • pp.68-75
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    • 2008
  • 화재시뮬레이션용 소프트웨어인 FDS (Fire Dynamics Simulator)의 수직벽 화재 시뮬레이션에 있어서의 문제점을 파악하기 위해, 수직벽 프로필렌 화재에 대한 시뮬레이션을 수행하였다. 성능기반설계 등에 널리 사용되고 있는 이 전산유체역학 모델에 포함되어있는 주요 매개변수의 기본값을 사용한 경우, 수직벽 화재에서는 정확도가 매우 낮음을 확인하였다. 프로필렌 연소율 $10.08g/m^2$-s과 $29.29g/m^2$-s에 대한 주요 매개변수의 조사를 수행한 결과, 스마고린스키 상수(Smagorinsky constant)가 기본값인 0.2에서 수직벽에 형성된 경계층이 층류로 예측되었다. 스마고린스키 상수가 0.1일 때 온도분포가 실험과 비교적 잘 일치하였으나 벽면에서의 열유속에는 큰 오차가 있음을 확인하였다.

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Patterns of Natural Convection around a Square Cylinder Placed Concentrically in a Horizontal Circular Cylinder (수평원관 내부에 위치한 동축정방형 물체 주위에서의 자연대류특성)

  • Chang, K. S.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.6 no.2
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    • pp.147-159
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    • 1982
  • 내부에 정방형, 외부에 원형인 두 정온동심수평관으로 이루어진 폐쇄공간에서 열부력으로 야기된 대류열전달 현상을 연구하였다. 주어진 비정규적 형상에서의 층류 정상 Boussinesq 유동을 해 석하기 위하여, 지구중력방향에 대하여 가능한 두 개의 대칭형 위치에 관하여, Galerkin 유한요 소법을 사용하였다. 이론의 결과를 확증하기 위하여 실험적으로도 온도측정과 유선의 가시화를 수행하였다. 정방형내관의 직각인 선단은 국소 및 총체열전달에 있어서 소극적인 역할을 하지만, 이들로 인한 경계층 유동의 박리는 발생하지 아니함을 보였다. 이 내관의 상부 수평면상에서는 유동속도와 온도구배가 낮기는 하나 확연한 대칭형의 열상승류(Plume)가 가능하였다. 내관의 벽면들이 지구중력방향에 관하여 .+-.45.deg.의 각을 이룰 경우 과류의 중심부가, Rayleigh수가 6.5*$10^{4}$보다 작을 때는 4개, 이보다 클때는 2개가 폐쇄공간 안에서 발생하였다.

A Study on flow characteristics around mountain using CFD method (풍속표준화를 위한 산악지형의 영향에 관한 수치해석적 연구)

  • Lee, Jong-Hoon;Kwon, Ji-Hyuk;Lee, Yeon-Won;Kim, Young-Duk
    • 유체기계공업학회:학술대회논문집
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    • 2006.08a
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    • pp.109-112
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    • 2006
  • Recently, when we conducted meteorological observations, complicated land or building around weather station has influenced on the wind distribution. So, we should understand the effect of geometry to get more accurate data. In this study, we analyze the ideal geometry whose shape is hemisphere using CFD method. And then we apply this method to real geometry. And we investigate the velocity at the location of weather station. As the results, we could find out an important relationship between geometry and flow field.

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A Numerical Analysis of Characteristics of Combined Heat Transfer in Laminar Layer Along Cylinderical Periphery by P-N Method (P-N 근사법을 이용한 원관주위 층류 경계층내 조합 열전달 전달 특성 해석)

  • 이종원;이창수
    • Journal of Advanced Marine Engineering and Technology
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    • v.19 no.2
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    • pp.10-19
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    • 1995
  • Heat trnasfer for absorbing and emitting media in laminar layer along the cylinders has been analyzed. Governing equation are transformed to local nonsimilarity equations by the dimensional analysis. The effects of the Stark number, Prandtl number, Optical radius and wall emissivity are mainly investigated. For the formal solution a numerical integration is performed and the results are compared with those obtained by P-1 and P-3 approximation. The results show that boundary layers consist of conduction-convection-radiation layer near the wall and convection-radiation layer far from the wall. As the Stark number of wall emissivity increases the local radiative heat flux is increased. The Pradtl number or curvature variations do not affect the radiative heat flux from the wall, but The Prandtl number or wall emissivity variations affect the conduction heat flux. Consequently the total heat flux from the wall are affected by the Prandtl number or wall emissivity variation.

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