• Title, Summary, Keyword: turbulent flow

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Large Eddy Simulation of Turbulent Pipe Flow (LES에 의한 원관 내 난류의 유동 해석)

  • 고상철
    • Journal of the Korean Society of Marine Engineering
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    • v.27 no.3
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    • pp.437-446
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    • 2003
  • A large eddy simulation (LES) is performed for turbulent pipe flow. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The effects of grid fineness which can be well prediction of turbulent behavior in near wall region is investigated. The subgrid scale turbulent models are applied and validated emphasis is placed on the flow details of turbulent pipe flow The calculated Reynolds number is 360 based on the wall shear velocity and the inlet pipe diameter. The predicted turbulent statistics are evaluated by comparing with the DNS data of turbulent pipe flow Performed by Eggels et al. The agreement of LES with DNS data is shown to be satisfactory. The proper grid fineness of the well prediction of turbulent pipe flow is suggested and the turbulent behavior is analyzed by depict the contour plot of fluctuating velocity components.

Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models

  • Sato, T.;Hagishima, A.;Ikegaya, N.;Tanimoto, J.
    • International Journal of High-Rise Buildings
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    • v.2 no.2
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    • pp.105-113
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    • 2013
  • Recent studies proved turbulent flow properties in high-rise building models differ from those in low-rise building models by comparing turbulent statistics. Although it is important to understand the flow characteristics within and above high-rise building models in the study of urban environment, it is still unknown and under investigation. For this reason, we performed wind tunnel experiment using Particle Image Velocimetry (PIV) to investigate and identify the turbulent flow properties and characteristic flow patterns in high-rise building models. In particular, we focus on instantaneous flow field near the canopy and extracted flow field when homogeneous flow field were observed. As a result, six characteristic flow patterns were identified and the relationship between these flow patterns and turbulent organized structure were shown.

REYNOLDS NUMBER EFFECTS ON TURBULENT PIPE FLOW PART II. INSTANTANEOUS FLOW FIELD,HIGHER-ORDER STATISTICS AND TURBULENT BUDGETS (난류 파이프 유동에서의 레이놀즈 수 영향: Part II. 순간유동장, 고차 난류통계치 및 난류수지)

  • Kang, Chang-Woo;Yang, Kyung-Soo
    • Journal of computational fluids engineering
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    • v.16 no.4
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    • pp.100-109
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    • 2011
  • Large eddy simulation(LES) of fully developed turbulent pipe flow has been performed to investigate the effect of Reynolds number on the flow field at $Re_{\tau}$=180, 395, 590 based on friction velocity and pipe radius. A dynamic subgrid-scale model for the turbulent subgrid-scale stresses was employed to close the governing equations. The mean flow properties, mean velocity profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The Reynolds number effects were observed in the higher-order statistics(Skewness and Flatness factor). Furthermore, the budgets of the Reynolds stresses and turbulent kinetic energy were computed and analyzed to elucidate the effect of Reynolds number on the turbulent structures.

Drag Prediction of Elliptic Airfoil (타원형 에어포일의 항력 예측)

  • Kim C. W.;Park Y. M.;Kwon K. J.;Lee J. Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.23-26
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    • 2004
  • Drag prediction is sought for the aifoil having laminar and turbulent flow characteristics with CFD code being unable to predict transition to turbulent flow. Laminar flow simulation presents some insight to the transition position. Separate simulations with laminar and turbulent flow and their combination estimate the drag of the airfoil containing laminar and turbulent flow characteristics.

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A Study on Pressure Distribution, Wall Shear Stress and Friction Factor of Developing Turbulent Pulsating Flows in a Square Duct(Ⅰ), -Experimental Analysis- (정4각단면덕트의 입구영역에서 난류맥동유동의 압력분포, 전단응력분포와 관마찰계수에 관한 연구(Ⅰ), - 실험해석-)

  • Park, Gil-Mun;Cho, Byeong-Gi;Koh, Yeong-Ha;Bong, Tae-Geun
    • Journal of the Korean Society of Marine Engineering
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    • v.20 no.5
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    • pp.58-67
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    • 1996
  • In the present study, the pressure distribution, wall shear stress distribution and friction factor of developing turbulent pulsating flows are investigated theoretically and experimentally in the entrance region of a square duct. The pressure distribution for turbulent pulsating flows are in good agreement with the theoretical values. The time-averaged pressure gradients of the turbulent pulsating flows show the same tendency as those of turbulent steady flows as the time-averged Reynolds number $(Re_{ta})$ increase. Mean shear stresses in the turbulent pulsating flow increase more in the inlet flow region than in the fully developed flow region and approach to almost constant value in the fully developed flow region. In the turbulent pulsating flow, the friction factor of the quasi-steady state flow $({\lambda}_{q, tu})$ follow friction factor's law in turbulent steady flow. The entrance length of the turbulent pulsating flow is not influenced by the time-averaged Reynolds number $(Re_{ta})$ and it is about 40 times as large as the hydraulic diameter.

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Pipe Friction in Transition Flow (천이류에서의 관마찰)

  • Yoo, Dong Hoon
    • Journal of The Korean Society of Civil Engineers
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    • v.13 no.4
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    • pp.101-109
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    • 1993
  • On the basis of Nikuradse laboratory experiments. two transition flow regimes are defined with respect to the characteristics of boundary layer. One is the transitional turbulent flow which has a transitional characteristics between smooth turbulent flow and rough turbulent flow, and the other may be called as transitional laminar flow which has transitional features between laminar flow and turbulent flow. The laboratory results of Nikuradse are carefully re-examined, and the flow regions are clearly defined. The velocity profile of the transitional turbulent flow is described by newly formulated equation, and the Darcy-Weisbach friction coefficient for the transitional turbulent flow is determined based on the theoretical form of profile equation, which is far better accurate than Colebrook-White equation. Difficulties still arise for the description of velocity profile when the flow undergoes from laminar to turbulent. In this case a linear interpolation procedure is proposed for the estimation of friction coefficient.

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Visualization of Turbulent Flow around a Sphere (구 주위 난류유동에 관한 가시화 연구)

  • Jang, Young-Il;Lee, Sang-Joon
    • 유체기계공업학회:학술대회논문집
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    • pp.401-402
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    • 2006
  • The turbulent flow around a sphere was investigated using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5300, 11000 and PIV measurements in a circulating water channel. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. The mean velocity field measured using a PIV technique in x-y center plane demonstrates the detailed near-wake structure such as nearly symmetric recirculation region, two toroidal vortices, laminar separation, transition and turbulent eddies. The PIV measurements of turbulent wake in y-z planes show that a recirculating vortex pair dominates the near-wake region.

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Investigation on the Turbulent Swirling Flow Field within the Combustion Chamber of a Gun-Type Gas Burner (Gun식 가스버너의 연소실내 난류 선회유동장 고찰)

  • Kim, Jang-Kweon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.9
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    • pp.666-673
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    • 2009
  • The turbulent swirling flow field characteristics of a gun-type gas burner with a combustion chamber were investigated under the cold flow condition. The velocities and turbulent quantities were measured by hot-wire anemometer system with an X-type probe. The turbulent swirling flow field in the edge of a jet seems to cause a recirculation flow from downstream to upstream due to the unbalance of static pressure between a main jet flow and a chamber wall. Moreover, because the recirculation flow seems to expand the main jet flow to the radial and to shorten it to the axial, the turbulent swirling flow field with a chamber increases a radial momentum but decreases an axial as compared with the case without a chamber from the range of about X/R=1.5. As a result, these phenomena can be seen through all mean velocities, turbulent kinetic energy and turbulent shear stresses. All physical quantities obtained around the slits, however, show the similar magnitude and profiles as the case without a chamber within the range of about X/R=1.0.

Numerical Investigation on Turbulent Flow Characteristics in the Gap connecting with Two parallel Channels using Large Eddy Simulation (평행한 두 사각유로를 연결하는 협소유로내의 난류유동 특성에 관한 대형 와 수치 모사)

  • Hong, Seong-Ho;Seo, Jeong-Sik;Shin, Jong-Keun;Choi, Young-Don
    • Proceedings of the SAREK Conference
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    • pp.55-60
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    • 2008
  • Turbulent flow characteristics on the gap of two parallel channels are investigated using LES(large eddy simulation) approach. Two parallel channels have the same cross-section area and are connected by the narrow channel named the gap. Turbulent flow near the gap makes the flow pulsation along the streamwise direction of two channels. The flow condition is the Reynolds number of $2.5{\times}10^{-5}$. We compared the predicted results with the previous experimental results and presented the axial mean velocity, turbulent intensities, Reynolds shear stresses and turbulent kinetic energy.

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An Experimental Study on Velocity Profiles and Turbulence Intensity of Developing Turbulent Pulsating Flows in the Entrance Region of a Square Duct

  • Park, G.M.;Koh, Y.H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.5 no.4
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    • pp.235-242
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    • 1993
  • The flow characteristics of developing turbulent pulsating flows are investigated experimentally in the entrance region of a square duct ($40mm{\times}40mm$ and 4,000mm). Mean velocity profiles, turbulence intensity and entrance length are measured by using a hot-wire anemometer system together with data acquisition and processing systems. It is found that the velocity waveforms are not changed in the fully developed flow region where that $x/Dh{\geq}40$. For turbulent pulsating flow, the turbulent components in the velocity waveforms increase as the dimensionless transverse position approaches the wall. Mean velocity profiles of the turbulent steady flows follow the one-seventh power law profile in the fully developed flow region. Turbulence intensity increases as the dimensionless transverse position increases from the center to the wall of the duct, and is slightly smaller in the accelerating phase than in the decelerating phase for the turbulent pulsating flows. The entrance length of the turbulent pulsating flow is about 40 times as large as the hydraulic diameter under the present experimental conditions.

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