• Title/Summary/Keyword: Square duct

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NUMERICAL SIMULATION OF INCOMPRESSIBLE LAMINAR ENTRY FLOWS IN A SQUARE DUCT OF $90^{\circ}$ BEND BY UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에 의한 정사각형 단면을 갖는 $90^{\circ}$ 곡관 층류유동의 수치해석)

  • Myong H. K.;Kim J. E.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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    • pp.81-85
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    • 2005
  • Three-dimensional steady incompressible laminar entry flows in a square duct of $90^{\circ}$ bend are numerically simulated by a new solution code(PowerCFD) using unstructured cell-centered method. Solutions are obtained with three unstructured grid types of hexahedron, prism and hybrid at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790. Interesting features of the flow are presented in detail. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a $90^{\circ}$ bend of a square duct with fully-developed entry flows. It is found that the code is capable of producing the nature of laminar flow in curved square duct with no grid type dependency.

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Study on the Similarity of Flows in an Orthogonally Rotating Square Duct and a Stationary Curved Square Duct (수직축을 중심으로 회전하는 직관과 정지한 곡관내의 유동 유사성에 관한 연구)

  • Lee, Gong-Hee;Baek, Je-Hyun
    • Proceedings of the KSME Conference
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    • 2001.06e
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    • pp.825-830
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    • 2001
  • A numerical study on a quantitative analogy of the fully developed flow between in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of two turbulent flows, the dimensionless parameters $K_{TR} = Re^{1/4}/\sqrt{Ro}$ and the Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to $K_{TC} = Re^{1/4}/\sqrt{{\lambda}}$ and curvature ratio, ${\lambda}$, in a stationary curved duct flow so that they have the same dynamical meaning as $K_{LR} = Re/\sqrt{Ro}$ and $K_{LC} = Re/\sqrt{{\lambda}}$ of the fully developed laminar flows. For the large values of Ro or A, it is shown that the flow field satisfies the asymptotic invariance property: there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of $K_L$ and $K_T$.

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Numerical Study on the Similarity between the Fully Developed Turbulent Flow in an Orthogonally Rotating Square Duct and that in a Stationary Curved Square Duct (수직축을 중심으로 회전하는 직관과 정지한 곡관 내에서의 완전 발달된 난류 유동의 유사성에 관한 수치적 연구)

  • Lee, Gong-Hui;Baek, Je-Hyeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.5
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    • pp.731-740
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    • 2001
  • A numerical study on the quantitative analogy between the fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and that in a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of the two flows, dimensionless parameters K(sub)TR=Re(sup)1/4/√Ro and Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to K(sub)TC=Re(sup)1/4/√λ and curvature ratio, λ, in a stationary curved duct flow so that they have the same dynamical meaning as those of the fully developed laminar flows. For the large values of Ro or λ, it is shown that the flow field satisfies the asymptotic invariance property, that is, there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of K(sub)TR and K(sub)TC.

A study on velocity profiles and inlet length of developing transitional pulsating flows in the entrance region of a square duct (정4각 덕트 입구영역에서 천이파동유동의 속도분포와 입구길이에 관한 연구)

  • 유영태;모양유;홍성삼
    • Journal of the korean Society of Automotive Engineers
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    • v.15 no.2
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    • pp.92-104
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    • 1993
  • In the present study, the velocity profiles and entrance length of developing transitional pulsating flows are investigated both analytically and experimentally in the entrance region of a square duct. The systems of conservation equations for transitional pulsating flows in a square duct are solved analytically by linearizing the non-linear convective terms. Analytical solutions are obtained in the form of infinite series for velocity pofiles. The experimental study for the air flow in a square duct(40mm*40mm*4000mm) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with a data acquisition and processing system. The distribution of velocity profiles( $u_{ps}$ / $u_{m,ta}$) in the decelerating period is higher than in the accelerating period. The distribution of the axial component of the axial component of velocity in the transitional flow is nearly uniform in the central region of the duct, and decrease rapidly near the wall. The entrance length correlation of the transitional pulsating flows in a square duct is obtained to be $L_{e}$/ $D_{h}$=0.83 $A_{1}$R $e_{ta}$ /(.omega. sup+1)$^{2}$TEX>

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Flows Characteristics of Developing Turbulent Pulsating Flows in a curved Square Duct (곡관덕트내의 입구영역에서 난류 맥동유도의 유동특성)

  • 봉태근
    • Journal of Advanced Marine Engineering and Technology
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    • v.23 no.4
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    • pp.533-542
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    • 1999
  • In this study the flow characteristics of developing turbulent pulsating flows in a square-sec-tional 180。 curved duct are investigated experimentally. The experimental study of air flow in a square-sectional curved duct is carried out to measure axial velocity distribution secondary flow velocity profiles and wall shear stress distributions by using a Laser Doppler Velocimetry system with the data acquisition and processing system of Rotating Machinery Resolver (RMR) and PHASE software at the entrance region of the duct which is divided into 7 sections from the inlet(${{\o}}=0_{\circ}$) to the outlet (${{\o}}=180_{\circ}$) in $30_{\circ}$ intervals. The results obtained from the study are summarized as follows: (1) The time-averaged critical Dean number of turbulent pulsating flow(De ta, cr) is greater than $75{\omega}+$ It is understood that the critical Dean number and the critical Reynolds number are related to the dimensionless angular frequency in a curved duct. (2) Axial velocity profiles of turbulent pulsating flows are of an annular type similar to those of turbulent stead flows. (3) Secondary flows of trubulent pulsating flows are strong and complex at the entrance region. As velocity amplitudes(A1) become larger secondary flows become stronger. (4) Wall shear stress distributions of turbulent pulsating flows in a square-sectional $180_{\circ}$ curved duct are exposed variously in the outer wall and are stabilized in the inner wall without regard to the phase angle.

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Velocity Profiles and Entrance Length of Transitional Oscillatory Flows in the Entrance Region of a Square Duct (정(正)4각(角)덕트 입구영역(入口領域)에서 천이(遷移) 진동유동(振動流動)의 입구(入口)길이와 속도분포(速度分布))

  • Choi, J.H.;Choi, B.M.;Yoo, Y.T.
    • Journal of Biosystems Engineering
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    • v.18 no.3
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    • pp.275-287
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    • 1993
  • The flow characteristics of the transitional oscillatory flows are investigated analytically and experimentally in the entrance region of a square duct. The systems of conservation equations are analytically solved by linearizing the non-linear convective terms for the developing transitional oscillatory flows in a square duct. The analytical solutions are obtained in the form of infinite series for the velocity profiles. The experimental study for the air flow in a square duct is carried out to measure the velocity profiles and waveforms by using a hot-wire anemometer with the data acquisition and processing systems. The theoretical and experimental results provide the major characteristics of the developing transitional oscillatory flows, such as velocity profiles, velocity waveforms, and entrance length. The velocity profiles in the decelerating phase are larger than those in the accelerating phase for the developing transitional oscillatory flows. The correlations of the entrance length of the transitional oscillatory flows in a square duct are found to be $Le/Dh=K{\cdot}Re_{os}/2({\omega}^+)^2$, where K is 1.23 of an experimental constant.

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Axial Direction Velocity and Wall shear Stress Distributions of Turbulent Steady Flow in a Curved Duct (곡관덕트에 난류정상유동의 축방향 속도분포와 벽면전단응력분포)

  • 이홍구;손현철;이행남;박길문
    • Journal of Advanced Marine Engineering and Technology
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    • v.25 no.1
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    • pp.131-138
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    • 2001
  • In this paper, an experimental investigation of characteristics of developing turbulent steady flows in a square-sectional $180^{\circ}$curved duct is presented. The experimental study using air in a square-sectional $180^{\circ}$ curved duct carryed out to measure axials direction velocity and wall shear stress distrbutions by using Laser Dopper Velocimeter(LDV) system with data acquistion and processing the system of FIND6260 softwere at 7 sections from the inlet($\phi=0^{\circ}$) to the outlet($\phi=180^{\circ}$) in $301^{\circ}$ intervals of a curved duct.

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A Characteristics of a Secondary flow in a Corner Section of Square Duct (정사각덕트의 코너부에서 이차유동 특성)

  • Joung, J.M.;Kim, J.H.;Yoo, Y.T.
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.753-758
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    • 2000
  • Heat engine and fluid machinery in the plant have to linked with various ducts network and the corresponding design have to be concerned about effectiveness and stability of system of plant. To optimum control and design system concerning stability, economization, operating effectiveness we have to exact analysis flow properties of a duct applying to fluid machinery, heat exchanger, cooling machine, air conditioning equipment. therefore, it is necessary to research the duct, heat transfer equipment, for increasing overall effectiveness of air conditioning system by suggesting basic data of the duct resulting from organic research. So we can contribute to technical development of the duct. In case of speeding up the flow rate of the duct, lots of wave velocity components are occurred the value of boundary layer resulting from developing the boundary layer at both walls of duct.

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A Study on Unsteady Flow measurement using Laser Doppler Velocimeter in Curved Duct (곡관에서 laser유속계를 이용한 비정상유동 계측에 대한 연구)

  • 조병기
    • Journal of Advanced Marine Engineering and Technology
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    • v.20 no.4
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    • pp.81-89
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    • 1996
  • In the present study, the unsteady in a square-selctional 180.deg. curved duct are experimentally investigated. The experimental study using air in a square-sectional 180.deg. curved duct is carried out to measure axial velocity distributions with data acquisition and processing system. In this system, Rotating Machinery Resolver(RMR) and PHASE Software are used to obtain the results of unsteady flows. In conclusion, the exact measurement of unsteady flow using LDV system depends upon uniformity of metreials, duct thickness, and scattered particles.

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Flow Characteristics of Developing Laminar Steady Flows in a Straight Duct Connected to a Square Curved Duct (곡관덕트에 연결된 정사각단면 직관덕트에서 증류정상유동의 유동장내 유동특성)

  • Sohn Hyun Chul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.5 s.236
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    • pp.545-553
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    • 2005
  • In the present study, The characteristics of developing steady laminar flows of a straight duct connected to a $180^{\circ}$ curved duct were examined In the entrance region through experimental measurement. Flow characteristics such as shear stress distributions, pressure distributions and friction coefficient experimentally in a square cross-sectional straight duct by using the PIV system. For the PIV measurement by particles produced from mosquito coils particles. The experimental data were obtained at 9 points dividing the test sections by 400mm. Experimental results can be summarized as follows. Critical Reynolds number, $Re_{cr}$ which indicates transition from laminar steady flow to transition steady flow was 2,150. Shear stress per unit length on the wall was stronger than that in the fully developed flow region. This was attributed to the fact that shear stress and pressure loss in the curvature of a duct were increased. Pressure distributions were gradually decreased irrespective of Reynolds number In the whole test section. This trends were in a good agreement with the reference results. Pipe friction coefficient in the steady state flow region was calculate from method of least squares. The co-relationship between fiction coefficient and Reynolds number was established as follow; ${\lambda}=56/Re$.