• Title/Summary/Keyword: bend flow

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Measurement of Turbulent Flows in a Square Sectioned $270^{\circ}$ Bend (열선 유속계에 의한 정사각형 단면의 270도 곡관에서의 난류유동 특성에 관한 연구)

  • Cho, Sok-Hyu;Chun, Kun-Ho;Lee, Gun-Hyee
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.467-472
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    • 2000
  • Most of the past experimental or analytical studies were performed for the curved bend with a square cross-section. Velocity profiles and Reynolds stresses of the turbulence flow in the 270 degree bend with circular cross-section were measured by a hot-wire anemometer. The mean velocity of primary flowing direction effected by the downstream of bend in the entry region of the bend. The flow in the inner part of the bend slowed the distribution velocity relatively large and unsymmetric phenomenon. In the strong secondary flow occurred when the flow passed in the region of 45 degree to 90 degree. The secondary flow appeared very large value in the neighbor region of inner wall.

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A Numerical Study on the Flow Development around a Rotating Square-Sectioned U-Bend(II) - Turbulent Flow - (회전하는 정사각 단면 U자형 곡관 내부의 유동 발달에 관한 수치적 연구(II) -난류 유동-)

  • Lee, Gong-Hee;Baek, Je-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.6
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    • pp.850-858
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    • 2002
  • The present study investigates in detail the combined effects of the Coriolis force and centrifugal force on the development of turbulent flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a curved region of U-bend, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal force due to the curvature of U-bend. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct. On the other hand, under negative rotation, where these two forces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces. Under the condition that the value of Rossby number and curvature ratio is large, the flow field in a rotating U-bend can be represented by two dimensionless parameters : $K_{TC}$ =Re $\sfrac{1}{4}$√λand a body force ratio F=λ/Ro. Here, $K_{TC}$ has the same dynamical meaning as $K_{TC}$ =Re√λ for laminar flow.

Study of Superelevation of Ichon-Banpo Bend Flow in the Han River (한강 이촌-반포 만곡부의 편수위 연구)

  • Lee, Jong-Kyu;Kim, Joo-Young;Park, Hyun-Jin;Kang, Ji-Ye
    • Proceedings of the Korea Water Resources Association Conference
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    • 2009.05a
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    • pp.810-814
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    • 2009
  • Two dimensional steady and unsteady numerical models are applied to bend reaches of the Lower Han River and the superelevation at the Ichon-Banpo bend area of Han River was observed. The flow characteristics in the meandering river are complicated due to the effects of the centrifugal force. The centrifugal force makes the outside water surface level increase and the outside velocity decrease. To study this complex flow studying two dimensional flow is important and useful to design flood control countermeasures, the analysis of sedimentation and the site selection of intake structures. Especially, the superelevation between inside and outside of the bend should be considered to determine the height of embankment. In this study, the water surface elevations in both bank sides of the bend were measured in two reaches during floods in 2007 and 2008. And then the two-dimensional simulation using RMA-2 model was carried out. The upstream and downstream boundary conditions on bend reaches were determined by FLDWAV which is one-dimensional unsteady model. Finally, the observed data are compared with simulation results and the results of the several superelevation formulas, and the flow characteristics of the bend are discussed.

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Measurement of turbulent flow characteristics of a rectangular duct with a 180.deg. bend by hot wire anemometer (열선유속계에 의한 180.deg.곡관을 갖는 직사각 단면덕트에서의 난류유동 특성의 측정)

  • 박호영;유석재;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.734-746
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    • 1990
  • Velocities and Reynolds stresses in 3-dimensional turbulent flow in rectangular ducts with a 180.deg. bend were measured by hot wire anemometer. Slant wire was rotated to 4 directions and I type wire was rotated to 2 directions and the voltage outputs of them were combined to obtain the mean velocities and Reynolds stresses. Flow characteristics in the 1.5:1 and 2:1 cross secioned 180.deg. bend were measured and the results were compared with the data from Moon for the square sectioned 180.deg. bend flow. Flows in rectangular sectioned 180.deg. bend show the reduction in secondary flow and therefore the reduction of double maximum in local mean velocities.

A Numerical Study on the Flow Development around a Rotating Square-Sectioned U-Bend (I) - Laminar Flow - (회전하는 정사각 단면 U자형 곡관 내부의 유동 발달에 관한 수치적 연구 (I) - 층류 유동)

  • Lee, Gong-Hui;Baek, Je-Hyeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.1
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    • pp.159-169
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    • 2002
  • The present study investigates in detail the combined effects of the Coriolis and centrifugal farce on the development of laminar flows in a square-sectioned U-bend rotating about an axis parallel to the center of bend curvature. When a viscous fluid flows through a rotating curved region, two types of secondary flow occur. One is caused by the Coriolis force due to the rotation of U-bend and the other by the centrifugal farce due to the curvature of U-bend. When the values of Rossby number and curvature ratio are large, the flow field in a rotating U-bend can be represented by two dimensionless parameters ; the Dean number K$\_$LC/=Re/√λ and a body ratio F=λ/Po. For positive rotation, where the rotation is in the same direction as that of the main flow, both the Coriolis force and the centrifugal force act radially outwards, the directions of the two secondary flows are the same. Therefore, the flow structure is qualitatively similar to that observed in a stationary curved duct with a larger f7c. On the other hand, in case of negative rotation, where two farces act in opposite direction, more complex flow fields can be observed depending on the relative magnitudes of the forces.

Study on the Analysis of Turbulent Flow in a Rotating Square Sectioned $90^{\circ}$ Curved Duct (회전하는 정사각단면 $90^{\circ}$곡관내 난류유동에 관한 수치해석적 연구)

  • 이건휘;최영돈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2206-2222
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    • 1995
  • In this study, the characteristics of the three-dimensional turbulence flow in a rotating square sectioned 90.deg. bend were investigated by numerical simulation. And a dimensionless number, Coriolis force ratio, primarily subjected to the feature of the flow in the rotating 90.deg. bend was obtained as a result of one-dimensional theory. In the simulation study, low Reynolds number ASM developed by Kim(1991) in the square sectioned 180.deg. bend flow was modified in order to consider the rotational effects in the testing flows. In the near wall region of low Reynolds number, four turbulence models were employed and compared in order to find the most appropriate model for the analysis of the rotating 90.deg. bend flow. By comparison of the results with the experimental data, it is shown that low Reynolds number Algebraic Stress Model with rotating terms reflects most correctly the rotational effects. As the results of this study, centrifugal forces associated with the curvature of the bend and Coriolis forces and centripetal forces associated with the rotation affect directly both the mean motion and the turbulent fluctuations. Their actions on the mean flow are to induce a secondary motion while their effects on turbulence are to modify the pressure strain.

Measurement of Developing Turbulent Flows in a 90-Degree Square Bend with Spanwise Rotation (횡방향으로 회전하는 90도 정사각 단면 곡덕트에서 발달하는 난류유동의 측정)

  • Kim, Dong-Chul;Choi, Young-Don;Lee, Kun-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.2
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    • pp.206-214
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    • 2003
  • Mean flow and turbulence properties of developing turbulent flows in a 90 degree square bend with spanwise rotation were measured by a hot-wire anemometer. A slanted wire is rotated into 6 orientations and the voltage outputs from them are combined to obtain the mean velocity and Reynolds stress components. The combinative effects of the centrifugal and Coriolis forces due to the curvature and the rotation of bend on the mean motion and turbulence structures are investigated experimentally. Results show that the two body forces can either enhance or counteract each other depending on the flow direction in the bend.

Effect of Secondary Flow on a Premixed Flame in the U-bend Nozzle (U-곡관 노즐에서 예혼합화염에 미치는 이차 유동의 영향)

  • Kim, H.G.;Cha, M.S.;Chung, S.H.
    • 한국연소학회:학술대회논문집
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    • 1998.10a
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    • pp.91-101
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    • 1998
  • The effect of secondary flow on both methane/air and propane/air premixed flame was investigated experimentally. By changing the radius of curvature, various flame behavior was observed. In the V-bend nozzles, flame surface is deformed from axisymmetry. As the exit velocity increased, flame lifted off partially. When the radius of curvature of the V-bend increased, the region where premixed flame is entirely on the rim increased. Since the axial velocity field is changed due to the secondary flow effect, comparison of V-bend and straight tube with the same diameter shows larger V-bend nozzle exit velocity for both flash back and flame blowout. The flame characteristics are mapped with a equivalence ratio, a velocity, and a nozzle radius of curvature. To identify physical reasoning on the flame surface deformation, numerical calculations are conducted. OH radical distributions in flames are visualized by PLIF technique.

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Numerical Study on the Turbulent Flow in the 180^{\circ}$ Bends Decreasing Cross-sectional Aspect Ratio (단면의 폭이 감소하는 180^{\circ}$ 곡덕트 내 난류유동의 수치해석적 연구)

  • 김원갑;최영돈
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.12
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    • pp.1056-1062
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    • 2002
  • This paper reports the characteristics of the three dimensional turbulent flow in the 180 degree bends with decreasing cross-sectional area by numerical method. Calculated pressure and velocity, Reynolds stress distributions are compared to the experimental data. Turbulence model employed are low Reynolds number k-epsilon model and algebraic stress model. The results show that the main vortex generated from the inlet part of the bend maintained to outlet of the bend because of the contraction of cross-sectional area. The rate of increase of turbulent kinetic energy through the bend are lower than that of mean flow. Secondary flow strength of the flow is lower about 60% than that of square duct flow.

Measurement of Developing Turbulent Flows in a 90-Degree Square Bend with Spanwise Rotation

  • Choi Young Don;Kim Dong Chul;Lee Kun Hee
    • Journal of Mechanical Science and Technology
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    • v.19 no.7
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    • pp.1503-1516
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    • 2005
  • Mean flow and turbulence properties of developing turbulent flows in a 90 degree square bend with span-wise rotation are measured by a hot-wire anemometer. A slanted wire is rotated into 6 orientations and the voltage outputs from them are combined to obtain the mean velocity and the Reynolds stress components. Combined effects of the centrifugal and Coriolis forces due to the curvature and the rotation of the bend on the mean motion and turbulence structures are investigated experimentally. Results show that the two body forces can either enhance or counteract each other depending on the flow direction in the bend.