• 제목/요약/키워드: Turbulent Separated Flow

검색결과 78건 처리시간 0.022초

국소교란에 의한 박리 재부착 유동에서의 난류 열전달 수치해석 (Numerical Simulation of Turbulent Heat Transfer in Locally-Forced Separated and Reattaching Flow)

  • 리광훈;성형진
    • 대한기계학회논문집B
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    • 제25권1호
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    • pp.87-95
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    • 2001
  • A numerical study was made of heat transfer in locally-forced turbulent separated and reattaching flow over a backward-facing step. The local forcing was given to the flow by means of sinusoidally oscillating jet from a separation line. A Rhee and Sung version of the unsteady $\kappa$-$\varepsilon$-f(sub)u model and the diffusivity tensor heat transfer model were employed. The Reynolds number was fixed at Re(sub)H=33,000 and the forcing frequency was varied in the range 0$\leq$fH/U(sub)$\infty$$\leq$2. The condition of constant heat flux was imposed at the bottom wall. The predicted results were compared and validated with the experimental data of Chun and Sung and Vogel and Eaton. The enhancement of heat transfer in turbulent separated and reattaching flow by local forcing was evaluated and analyzed.

자유흐름 난류강도가 후향계단유동에 미치는 영향에 대한 실험 (An Experiment on the Effects of Free Stream Turbulence Intensity on the Backward-Facing Step Flow)

  • 김사량;유정열
    • 대한기계학회논문집
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    • 제19권9호
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    • pp.2297-2307
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    • 1995
  • An experimental study on the structure of a separated shear layer downstream of the backward-facing step has been performed by examining mean flow and turbulent quantities in terms of free stream turbulence. When free stream turbulence exists, the entrainment rate of the separated shear layer and the flow rate in the recirculation region are enhanced, resulting in shorter reattachment length. The production and diffusion terms in the turbulent kinetic energy balance are shown to increase more than the dissipation term does. Rapid decrease of the pressure-strain term in the shear stress balance implies the enhancement of the three-dimensional motion by free stream turbulence.

후향 계단 주위 난류 박리 유동에 대한 비정상 후류의 영향 (Influence of Unsteady Wake on Turbulent Separated Flows over a Backward-Facing Step)

  • 전세종;성형진
    • 대한기계학회논문집B
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    • 제27권12호
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    • pp.1708-1715
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    • 2003
  • An experimental study was made of turbulent separated and reattaching flow over a backward-facing step, where unsteady wake was generated by a spoked-wheel type wake generator with cylindrical rods in front of the separated flow. The influence of unsteady wake was scrutinized in terms of the rotating speed of the wake generator (0$\leq$S $t_{H}$$\leq$0.4). A conditional averaging technique in corporation with SBF was employed to elucidate the influence of the unsteady wake on the large-scale vortical structures of the separated flow. Special attention was made during two-dimensional measurements of wall-pressure with or without unsteady wake. The wall-pressure fluctuations were used to predict dipole sound source by Curie's integral formula. It was found that the reduction of the dipole sound source was due to the reduction of turbulent kinetic energy by unsteady wake in the recirculation region.n.

난류박리 및 재부착 유동의 해석을 위한 저레이놀즈수 4-방정식 난류모형의 개발 (A Low-Reynolds-Number 4-Equation Model for Turbulent Separated and Reattaching Flows)

  • 이광훈;성형진
    • 대한기계학회논문집
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    • 제19권8호
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    • pp.2039-2050
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    • 1995
  • The nonlinear low-Reynolds-number k..epsilon. model of park and Sung is extended to predict the turbulent heat transports in separated and reattaching flows. The equations of the temperature variance( $k_{\theta}$ and its dissipation rate(.epsilon.$_{\theta}$ are solved, in concert with the equations of the turbulent kinetic energy(k) and its dissiation rate(.epsilon). In the present model, the near-wall effect and the non-equilibrium effect are fully taken into consideration. The validation of the model is then applied to the turbulent flow behind a backward-facing step and the flow over a blunt body. The predicted results of the present model are compared and evaluated with the relevant experiments.

저항감소를 위한 물체후방의 형상설계에 관한 LES 해석 (Large Eddy Simulations on the Configuration Design of Afterbodies for Drag Reduction)

  • 박종천;강대환;전호환
    • 한국해양공학회지
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    • 제17권5호
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    • pp.1-10
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    • 2003
  • When a body with slant angle behind its shoulder is moving at a high speed, the turbulent motion around the afterbody is generally associated with the flow separation, and determines the normal component of the drag. By changing the slant angle of the afterbody, the drag coefficients can be changed, drastically. Understanding and controlling the turbulent separated flows has significant importance for the design of optimal configuration of the moving bodies. In this paper, a new Large Eddy Simulation technique has been developed to investigate turbulent vortical motions around the afterbodies, using slant angle. By understanding the structure of the turbulent flow around the body, the new configuration of afterbodies is designed to reduce the drag of body, and the nonlinear effects, due to the interaction between the body configuration and the turbulent separated flows, are investigated by use of the developed LES technique.

2차원 직사각형 덕트 내부에 돌기부를 갖는 흐름의 동결특성에 관한 연구 (Freezing Characteristics in a Horizontal Rectangular Channel with the Two-Dimensional Protuberances)

  • 오철
    • Journal of Advanced Marine Engineering and Technology
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    • 제27권6호
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    • pp.721-727
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    • 2003
  • Freezing of turbulent water flow between two horizontal cooled parallel plates with the separated region has been investigated experimentally. The flow separation was induced by vertical plates (two-dimensional plates) situated at the inlet of the rectangular channel. The degree of flow separation was varied by employing vertical thin plates with various heights. Three kinds of the vertical plates with 8.0, 9.8 and 12.5 mm in height were utilized. The Reynolds number and cooling temperature ratio were ranged from $3.45\times10^3 to 1.73\times10^4$ and 7.0 to 20.0 respectively, The measurements show that the flow separation influenced remarkably on the local ice formation characteristics. The location of the first ice layer and the average heat transfer at the ice surface were found be correlated as a function of the Reynolds number, the cooling temperature ratio, and the orifice height ratio.

Numerical study of turbulent wake flow behind a three-dimensional steep hill

  • Ishihara, Takeshi;Hibi, Kazuki
    • Wind and Structures
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    • 제5권2_3_4호
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    • pp.317-328
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    • 2002
  • A numerical investigation on the turbulent flows over a three-dimensional steep hill is presented. The numerical model developed for the present work is based on the finite volume method and the SIMPLE algorithm with a non-staggered grid system. Standard $k-{\varepsilon}$ model and Shih's non-linear model are tested for the validation of the prediction accuracy in the 3D separated flow. Comparisons of the mean velocity and turbulence profiles between the numerical predictions and the measurements show good agreement. The Shih's non-linear model is found to predict mean flow and turbulence better than the Standard $k-{\varepsilon}$. Flow patterns have also been examined to explain the difference in the cavity zone between 2D and 3D hills.

압축성 박리 유동에서 Realizability 조건의 영향 (INFLUENCE OF THE REALIZABILITY CONDITION ON TURBULENT SEPARATED FLOW SIMULATIONS)

  • 박수형;사정환;김지웅
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2007년도 춘계 학술대회논문집
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    • pp.142-147
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    • 2007
  • The realizability condition has been applied to modern turbulence models, Simulations are performed to compare ${\kappa}-{\omega}$ turbulence models imposing the realizability condition. An improvement to the ${\kappa}-{\varepsilon}$ turbulence model is also presented and shown to lead to better agreement with data for supersonic base flows. The improvement is achieved by imposing a grid-independent realizability constraint in the Launder-Sharma ${\kappa}-{\varepsilon}$ model. Numerical results for several test problems show a critical role of the realizability constraint in the prediction of separated flows.

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축대칭 하향단흐름에서 자유흐름 난류강도의 영향 (Effects of the free Stream Turbulence Intensity on the Flow Over an Axisymmetric Backward-Facing Step)

  • 양종필;김경천;부정숙
    • 대한기계학회논문집
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    • 제19권9호
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    • pp.2328-2341
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    • 1995
  • An experimental study on the flow over the axisymmetric backward-facing step was carried out. The purposes of the present study are to investigate the effect of the free stream turbulence intensity on the reattachment length and to understand the turbulence structure of the recirculating flows. Local mean and fluctuating velocity components were measured in the separated and reattaching axisymmetric turbulent boundary layer over the wall of convex cylinder placed in a water tunnel by using 2-color 4-beam fiber optics laser Doppler velocimetry. As the free stream turbulence intensity increased, the reattachment length became shorter due to the enhanced mixing in the separated shear layer. It was also observed that the reverse flow velocity and turbulent kinetic energy increase with increasing free stream turbulence intensity. Spectral data and flow visualization showed that low-frequency motions occur in the separated flow behind a backward-facing step. These motions have a significant effect on the time-averaged turbulence data.

오목면 및 볼록면에 존재하는 난류경계층유동과 경사지게 분사되는 난류제트의 유동특성 (Flow Characteristics of Inclined Turbulent Jet Issuing into Turbulent Boundary Layer Developing on Concave and Convex Surfaces)

  • 이상우;이준식;이택식
    • 대한기계학회논문집
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    • 제16권2호
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    • pp.302-312
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    • 1992
  • Three dimensional velocity measurements of a 35.deg. inclined jet issuing into turbulent boundary layer on both concave and convex surfaces have been conducted. To investigate solely the effect of each curvature on the flow field, streamwise pressure variations are minimized by adjusting the shape of the opposite wall in the curved region. From the measured velocity components, streamwise mean vorticities are calculated to determine jet-crossflow interface. The results on convex surface show that the injected jet is separated from the wall and the bound vortex maintains its structure far downstream. On concave surface, the secondary flow in the jet cross-sections are enhanced and in some downstream region from the jet exit, the flow on the concave surface has been developed to Taylor-Gortler vortices