• Title/Summary/Keyword: Turbulent Pipe Flows

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Turbulence in temporally decelerating pipe flows (시간에 대해 감속하는 난류 파이프 유동에 관한 연구)

  • Jeong, Wongwan;Lee, Jae Hwa
    • Journal of the Korean Society of Visualization
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    • v.14 no.1
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    • pp.46-50
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    • 2016
  • Direct numerical simulations (DNSs) of turbulent pipe flows with temporal deceleration were performed to examine response of the turbulent flows to the deceleration. The simulations were started with a fully-developed turbulent pipe flow at the Reynolds number, $Re_D=24380$, based on the pipe radius and the laminar centerline velocity, and three different constant temporal decelerations were applied to the initial flow with varying dU/dt = -0.001274, -0.00625 and -0.025. It was shown that the mean flows were greatly affected by temporal decelerations with downward shift of log law, and turbulent intensities were increased in particular in the outer layer, compared to steady flows at a similar Reynolds number. The analysis of Reynolds shear stress showed that second- and fourth-quadrant Reynolds shear stresses were increased with the decelerations, and the increase of the turbulence was attributed to enhancement of outer turbulent vortical structures by the temporal decelerations.

Fluid and Heat Transfer Characterization of Surfactant Turbulent Pipe Flows (계면활성제가 첨가된 관내 난류의 열유동 특성에 관한 고찰)

  • Shin, Kwang-Ho;Yoon, Hyung-Kee;Chang, Ki-Chang;Ra, Ho-Sang
    • Proceedings of the SAREK Conference
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    • 2006.06a
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    • pp.982-987
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    • 2006
  • The fluid mechanics and heat transfer of surfactant turbulent pipe flows are characterized with particular emphasis on the effects of surfactant concentration and solution temperature on drag reduction and heat transfer reduction. The test fluids are the surfactant solutions of DR-IW616 supplied by Akzo Nobel Chemical in concentration of $100{\sim}3000ppm$. The solution temperatures studied are $5^{\circ}C$ to $50^{\circ}C$. The critical values of surfactant concentration and solution temperature are clearly identified for drag reduction phenomena.

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Validation of Magnetic Resonance Velocimetry by Turbulent Pipe Flow (자기공명유속계를 이용한 난류 유동장 가시화)

  • Lee, Jeesoo;Song, Simon;Cho, Jee-Hyun
    • Journal of the Korean Society of Visualization
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    • v.12 no.1
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    • pp.35-42
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    • 2014
  • Magnetic resonance velocimetry (MRV) is a versatile flow visualization technique using magnetic resonance imaging machine developed for the medical purpose. Recently, MRV is often utilized to analyze engineering flows due to its superior features of MRV such as capabilities of measuring flows with complicated, opaque flow geometry unlike optical techniques, 3-dimensional volumetric velocity vectors within a few hours, and etc. The purpose of this study was to validate the MRV data and evaluate the accuracy of the mean velocity profiles that we acquired for a turbulent flow in a circular pipe using a MR machine installed in Korea Basic Science Institute, Ochang, Korea. In addition, we briefly describe a procedure of parameter optimization for the operation of MRV. The results indicate that the MRV measurements provided well resolved mean velocity fields with a quite reasonable accuracy according to the inner and outer layer scaling laws of the turbulent pipe flows.

REYNOLDS NUMBER EFFECTS ON MASS TRANSFER IN TURBULENT PIPE FLOW: PART II. INSTANTANEOUS CONCENTRATION FIELD, HIGHER-ORDER STATISTICS AND MASS TRANSFER BUDGETS (난류 파이프 유동 내 물질전달에 대한 레이놀즈 수 영향: Part II. 순간농도장, 고차 난류통계치 및 물질전달수지)

  • Kang, Chang-Woo;Yang, Kyung-Soo
    • Journal of computational fluids engineering
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    • v.17 no.3
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    • pp.59-67
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    • 2012
  • Large Eddy Simulation(LES) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of Reynolds number on the concentration fields at $Re_{\tau}=180$, 395, 590 based on friction velocity and pipe radius. Dynamic subgrid-scale models for the turbulent subgrid-scale stresses and mass fluxes were employed to close the governing equations. Fully developed turbulent pipe flows with constant mass flux imposed at the wall are studied for Sc=0.71. The mean concentration profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The effects of Reynolds number on the turbulent mass transfer are identified in the higher-order statistics(Skewness and Flatness factor) and instantaneous concentration fields. The budgets of turbulent mass fluxes and concentration variance were computed and analyzed to elucidate the effect of Reynolds number on turbulent mass transfer. Furthermore, to understand the correlation between near-wall turbulence structure and concentration fluctuation, we present an octant analysis in the vicinity of the pipe wall.

REYNOLDS NUMBER EFFECTS ON MASS TRANSFER IN TURBULENT PIPE FLOW: PART I. MEAN CONCENTRATION FIELD AND LOW-ORDER STATISTICS (난류 파이프 유동 내 물질전달에 대한 레이놀즈 수 영향: Part I. 평균 농도장 및 저차 난류통계치)

  • Kang, Chang-Woo;Yang, Kyung-Soo
    • Journal of computational fluids engineering
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    • v.17 no.3
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    • pp.1-10
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    • 2012
  • Large Eddy Simulation(LES) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of Reynolds number on the concentration fields at $Re_{\tau}=180$, 395, 590 based on friction velocity and pipe radius. Dynamic subgrid-scale models for the turbulent subgrid-scale stresses and mass fluxes were employed to close the governing equations. Fully developed turbulent pipe flows with constant mass flux imposed at the wall are studied for Sc=0.71. The mean concentration profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. To show the effects of Reynolds number on the turbulent mass transfer, the mean concentration profile, root-mean-square of concentration fluctuations, turbulent mass fluxes, cross-correlation coefficient, turbulent diffusivity and turbulent Schmidt number are presented.

Friction Factor for Circular Pipe with Uniform Roughness (균일조도 원형관 마찰계수)

  • Yoo, Dong Hoon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.5
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    • pp.165-172
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    • 1993
  • On the basis of Nikuradse laboratory experiments conducted in circular pipe with uniform roughness, five flow regimes are defined with respect to the characteristics of boundary layer such as laminar, transition laminar, smooth turbulent, transition turbulent and rough turbulent flows. Two cases are found for the transition laminar flow: one for the transition between laminar flow and smooth turbulent flow and the other for the one between laminar flow and rough turbulent flow. They all can be clearly determined by the relative roughness or the ratio of pipe diameter to the roughness. Explicit functions are developed for the estimation of pipe friction factor for the various flow conditions including turbulent flow regimes, which have excellent agreement with the Nikuradse laboratory data.

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DNS of turbulent concentric annular pipe flow (동심 환형관 내의 난류유동의 직접수치모사)

  • Chung, Seo-Yoon;Rhee, Gwang-Hoon;Sung, Hyung-Jin
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.461-466
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    • 2000
  • Direct numerical simulations (DNS) is carried out to study fully-developed turbulent concentric annular pipe flow with two radius ratios at $Re_{Dh}\;=\;8900$. In case of $R_1/R_2\;=\;0.5$, the present result for the mean flow is in good agreement with the previous experimental data. Because of the transverse curvature effects, the distributions of mean flow and turbulent intensities are asymmetric in contrast to those of other fully-developed flows (channel and pipe flow). From the distributions of skewness of radial velocity fluctuations, it co be identified that all of the characteristics of channel, pipe and turbulent flow on a cylinder in axial flow can be appeared in concentric annular pipe flow.

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THE EFFECTS OF WALL BOUNDARY CONDITIONS ON MASS TRANSFER IN TURBULENT PIPE FLOW (난류 파이프 유동 내 물질전달에서의 경계조건 영향)

  • Kang, Chang-Woo;Yang, Kyung-Soo
    • Journal of computational fluids engineering
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    • v.17 no.2
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    • pp.42-52
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    • 2012
  • Direct Numerical Simulation(DNS) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of wall boundary conditions on the concentration fields at $Re_{\tau}$=180 based on friction velocity and pipe radius. Fully developed turbulent pipe flows for Sc=0.71 are studied with two different wall boundary conditions, namely, constant mass flux and constant wall concentration. The mean concentration profiles and turbulent mass fluxes obtained from the present DNS are in good agreement with the previous numerical results currently available. To investigate the effects of wall boundary condition on the turbulent mass transfer, the mean concentration profile, root-mean-square of concentration fluctuation, turbulent mass fluxes and higher-order statistics(Skewness and Flatness factor) are compared for the two cases. Furthermore, the budgets of turbulent mass fluxes and concentration variance were computed and analyzed to elucidate the effects of wall boundary conditions on the turbulent mass transfer.

The Effects of Copolymer Additives for Drag Reduction on Turbulent Flow (합성고분자첨가제의 난류마찰저항 감소효과 연구)

  • Kim, N.S.;Kim, C.B.;Kim, I.S.;Choi, H.J.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.5 no.3
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    • pp.207-216
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    • 1993
  • Experimental investigations have been carried out to find the effect of drag reduction caused by effective polymer additives in turbulent flows. The experiments were undertaken with a test section of 9.8mm pipe diameter and 3500 mm pipe length(L/D=357) in a closed loop, and Copolymer-X and Polyacrylamide(PAAM) were used as polymer additives for comparisons. The tests were carried out under different polymer concentrations, and the temperatures of the flow considered were $26^{\circ}C$, $60^{\circ}C$ at the flow velocity of 5.3 m/s. The rate of drag reduction obtained by Copolymer-X is found to be considerably higher than that of PAAM in turbulent flows. Copolymer-X is also found to be very reliable for mechanical degradation, which has not been the case in any other additives. It is concluded that Copolymer-X is considered to be one of the most effective agents as an additive especially for long time hydraulic transports. It is also found that polymer degradation in more likely at lower polymer concentrations in the turbulent flows.

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Prediction of strongly swirling turbulent flow downstream of an abrupt pipe expansion (원관내 급확대부 하류의 강선회난류에 관한 수치해석)

  • Kim, K.Y.;Chang, Y.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.1
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    • pp.23-32
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    • 1997
  • Swirling turbulent flows downstream of an abrupt axisymmetric expansion in a pipe are analyzed numerically by a second-order turbulence closure. Predictions for the flows without swirl and with strong swirl are obtained. The governing differential equations are discretized by finite volume approach. The results show that the on-axis recirculation induced by the strong swirl is correctly reproduced. The predictions for mean velocity components and turbulent normal stresses agree well with experimental data far downstream of expansion, but show large discrepancies in wall-bounded recirculation zone.

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