• Title/Summary/Keyword: Reynolds number

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Prediction of Fully Developed Turbulent Flow in a Square Duct with Nonlinear Low-Reynolds-Number κ-ε Models (비선형 저레이놀즈수 κ-ε 난류모델에 따른 정사각형 덕트내 완전 발달된 난류유동 예측)

  • Myong, Hyon-Kook,
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.6
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    • pp.821-827
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    • 2003
  • Fully developed turbulent flow in a square duct is numerically predicted with two nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ models. Typical predicted quantities such as axial and secondary velocities, turbulent kinetic energy and Reynolds stresses are compared in detail with each other. It is found that the nonlinear low-Reynolds-number ${\kappa}-{\varepsilon}$ model adopted in a commercial code is unable to predict accurately duct flows involving turbulence-driven secondary motion with the prediction level of secondary flows one order less than that of the experiment.

3-D Numerical Analysis on a low Reynolds Number Mixed Convection in a Horizontal Rectangular Channel (수평 사각채널 내 저 레놀즈수 혼합대류 유동의 3차원 수치해석)

  • Piao, Ri-Long;Bae, Dae-Seok
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2005.06a
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    • pp.210-215
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    • 2005
  • A three-dimensional numerical simulation is performed to investigate on a low Reynolds number mixed convection in a horizontal rectangular channel with the upper part cooled and the lower part heated uniformly. The three-dimensional governing equations are solved using a finite volume method. For convective term, the central differencing scheme is used and for the pressure correction, the PISO algorithm is used. Solutions are obtained for A=4, Pr=0.72, 10, 909, the Reynolds number ranging from $2.1{\times}10^{-2}$ to $1.2{\times}10^{-1}$, the Rayleigh number is $3.5{\times}10^4$. It is found that vortex roll structures of mixed convection in horizontal rectangular channel can be classified into three roll structures which affected by Prandtl number and Reynolds number.

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Flow Field Analysis of Smoke in a Rectangular Tunnel

  • Lee, Yong-Ho;Park, Sang-Kyoo
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.5
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    • pp.679-685
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    • 2009
  • In order to simulate a smoke or poisonous gas emergency in a rectangular tunnel and to investigate a better way to exhaust the smoke, the characteristics of smoke flow have been analyzed using flow field data acquired by Particle Image Velocimetry(PIV). Olive oil has been used as tracer particles with the kinematic viscosity of air, $1.51{\times}10^{-5}\;m^2/s$. The investigation has done in the range of Reynolds number of 1600 to 5333 due to the inlet velocities of 0.3 m/s to 1 m/s respectively. The average velocity vector and instantaneous kinematic energy fields with respect to the three different Reynolds numbers are comparatively discussed by the Flow Manager. In general, the smoke flow becomes more disorderly and turbulent with the increase of Reynolds number. Kinematic energy in the measured region increases with the increase of Reynolds number while decreasing at the leeward direction about the outlet region.

Characteristics of Sparkover Discharge in Flowing Air with Reynolds Numbers' Variable (Reynolds Number를 변수(變數)로한 유동공기(流動空氣)의 방전특성(放電特性)에 관한 연구)

  • Kim, Y.H.;Oh, J.Y.;Lee, K.S.;Lee, D.I.
    • Proceedings of the KIEE Conference
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    • 1990.07a
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    • pp.286-288
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    • 1990
  • This paper reports the characteristics of sparkover discharge in flowing air ranging from 0[m/s] to 30 [m/s] under the needle-needle gap. Flowing air duct of this investigation is circular tube. The important results obtained form this study are as follows. 1. the ratio of sparkover voltage to the Reynolds number decreases with increasing the Reynolds number. 2. The duration time of sparkover(t) decreases with increasing the Reynolds number. 3. the empirical equation obtained form this experiment is [ %]${\frac{Vs}{Re}}$ = A + $B{\varepsilon}^{C.Re}$ where A = 10.2 b = 125 c = -4.66 ${\times}$ $10^{-5}$

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Numerical Study on Combined Heat Transfer in NIR Dryer for Agricultural and Marine Products (근적외선 농수산물 건조기의 복합열전달특성에 관한 수치적 연구)

  • Choi, H.K.
    • Journal of Biosystems Engineering
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    • v.31 no.5 s.118
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    • pp.395-402
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    • 2006
  • Mixed heat transfer in an indirected NIR (Near Infrared Ray) dry chamber was investigated numerical analysis. It is Important that the miked heat transfer effects on double parameters which the Reynolds number and the position of emit lamp. Reynolds number are based on the outer diameter of the cylinder range from 103 to $30{\times}105$. Four difference heat transfer regimes of behavior are apparent: forced convection and radiation on the outer surface of the cylinder, pure conduction, pure natural convection and radiation between lamp surface and inner surface of the cylinder. The temperature and flow patterns are illustrated by iso-contour lines for the double parameters. Also presented are results on the convective heat transfer flux and the radiative heat transfer flux as increased with Reynolds number.

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.

FLOW INSTABILITY IN A BAFFLED CHANNEL FLOW (배플이 부착된 채널 유동의 불안정성)

  • Kang, C.;Yang, K.S.
    • Journal of computational fluids engineering
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    • v.16 no.1
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    • pp.1-6
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    • 2011
  • Flow instability is investigated in a two-dimensional channel with thin baffles placed symmetrically in the vertical direction and periodically in the streamwise dircetion. At low Reynolds numbers, the flow is steady and symmetric. Above a critical Reynolds number, the steady flow undergoes a Hopf bifurcation leading to unsteady periodic flow. As Reynolds number further increases, we observe the onset of secondary instability. At high Reynolds numbers, the two-dimensional periodic flow becomes three dimmensional. To identify the onset of secondary instability, we carry out Floquet stability analysis. We obseved the transition to 3D flow at a Reynolds number of about 125. Also, we computed dominant spanwise wavenumbers near the critical Reynolds number, and visualized vortical structures associated with the most unstable spanwise wave.

Experimental Study on the Unsteady Behavior of a Confined Impinging Slot Jet (국한 충돌 슬롯 제트의 비정상 거동에 대한 실험적 연구)

  • Kim, Kyung-Chun;Oh, Sung-Jin;Lee, In-Won
    • Journal of the Korean Society of Visualization
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    • v.3 no.2
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    • pp.57-62
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    • 2005
  • The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using proper orthogonal decomposition.

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A flow characteristic of non-newtonian fluid in coutte flow of concentric cylinder (동심원통속의 Coutte flow에 있어서 비 Newton 유체의 유동특성)

  • 권혁칠;이성노;부전유사
    • Journal of the korean Society of Automotive Engineers
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    • v.14 no.3
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    • pp.109-114
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    • 1992
  • The purpose of this study is to experimentally research the effects of polymer additives on turbulent transition of Couette flow between concentric cylinders when outer one is rotating and inner one is at rest; the diameter ratio being 0.2. Aqueous polymer solution generate the degradation phenomena in machine forming work, but this is not effected in about 10 minute at 5ppm. aqueous polymer solution testing. The Reynolds number, referred to the gap distance and rotation velocity of the outer cylinder, of turbulent transition is about 20000 for water flow. In the laminer region, the torque value is as same as theoretical one in the region of low Reynolds number, but becomes high with an increase in the Reynolds number. The polymer additives reduce the Reynolds number for turbulent transtition. In the turbulent region, the torque is remarkably reduced by the polymer additives, soluble polymer take down effect of turbulent transition boundary torque.

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Experimental and numerical aerodynamic investigation of a prototype vehicle

  • Akansu, Selahaddin Orhan;Akansu, Yahya Erkan;Dagdevir, Toygun;Daldaban, Ferhat;Yavas, Feridun
    • Wind and Structures
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    • v.20 no.6
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    • pp.811-827
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    • 2015
  • This study presents experimental and numerical aerodynamic investigation of a prototype vehicle. Aerodynamics forces examined which exerted on a prototype. This experimental study was implemented in a wind tunnel for the Reynolds number between $10^5-3.1{\times}10^5$. Numerical aerodynamic analysis of the vehicle is conducted for different Reynolds number by using FLUENT CFD software, with the k-$\varepsilon$ realizable turbulence model. The studied model aims at verifying the aerodynamic forces between experimental and numerical results. After the Reynolds number of $2.8{\times}10^5$, the drag coefficient obtained experimentally becomes independent of Reynolds number and has a value of 0.25.