• Title, Summary, Keyword: Turbulent channel flow

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PIV Analysis of a Pulsating Flow through a Square Channel

  • SAGA Tetsuo;UEDA Toshiyuki;TANIGUCHI Nobuyuki
    • 한국가시화정보학회:학술대회논문집
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    • pp.157-168
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    • 2004
  • The effects of pulsation in a pulsating flow through a rectangular channel have been investigated by Particle Image Velocimetry in both laminar and turbulent flow conditions. PIV results on a square channel (aspect ratio:1) have been reported on the cases of Reynolds number Re=80 in laminar and Re=8800 in turbulent region. For both in the laminar and turbulent regions, the influence of the pulsation onto the magnitude changes of the average velocity was negligible. In the turbulent region, the magnitude profiles of the stream-wise pulsating component obtained by the theoretical analysis based on the Stokes analogy were slightly different from the experimental ones due to the influence of the turbulent viscosities onto the pulsating flows.

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Effects of the Temporal Increase Rate of Reynolds Number on Turbulent Channel Flows (레이놀즈 수의 시간 증가율에 따른 난류 채널유동의 변화)

  • Jung, Seo Yoon;Kim, Kyoungyoun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.40 no.7
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    • pp.435-440
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    • 2016
  • Effects of the increase rate of Reynold number on near-wall turbulent structures are investigated by performing direct numerical simulations of transient turbulent channel flows. The simulations were started with the fully-developed turbulent channel flow at $Re_{\tau}=180$, then temporal accelerations were applied. During the acceleration, the Reynolds number, based on the channel width and the bulk mean velocity, increased almost linearly from 5600 to 13600. To elucidate the effects of flow acceleration rates on near-wall turbulence, a wide range of durations for acceleration were selected. Various turbulent statistics and instantaneous flow fields revealed that the rapid increase of flow rate invoked bypass-transition like phenomena in the transient flow. By contrast, the flow evolved progressively and the bypass transition did not clearly occur during mild flow acceleration. The present study suggests that the transition to the new turbulent regime in transient channel flow is mainly affected by the flow acceleration rate, not by the ratio of the final and initial Reynolds numbers.

Numerical Investigation of the Moving Wall Effects in Turbulent Channel Flows (난류채널유동에서 움직이는 벽면에 대한 수치연구)

  • Hwang, Jun Hyuk;Lee, Jae Hwa
    • Journal of the Korean Society of Visualization
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    • v.15 no.3
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    • pp.27-33
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    • 2017
  • Direct numerical simulations of turbulent channel flows with moving wall conditions on the top wall are performed to examine the effects of the moving wall on the turbulent characteristics. The moving wall velocity only applied to the top wall with the opposite direction to the main flow is systematically varied to reveal the sustained-mechanism for turbulence. The turbulence statistics for the Couette-Poiseuille flow, such as mean velocity, root mean square of the velocity fluctuations, Reynolds shear stress and pre-multiplied energy spectra of the velocity fluctuations, are compared with those of canonical turbulent channel flows. The comparison suggests that although the turbulent activity on the top wall increases with increasing the Reynolds number, that on the bottom wall decreases, contrary to the previous finding for the canonical turbulent channel flows. The increase of the turbulent energy on the top wall is attributed to not only the increase of the Reynolds number but also elongation of the logarithmic layer due to increase of the wall layer on the top wall. However, because the logarithmic layer is shortened on the bottom wall due to the decrease of the wall layer, the turbulence energy on the bottom wall decreases despite of the increase of the Reynolds number.

The study of turbulent flow structures in a wavy channel using direct numerical simulation (직접수치모사를 통한 Wavy Channel 내의 난류 유동 구조의 연구)

  • Lee, Dae-Sung;Ha, Man-Yeong;Yoon, Hyun-Sik;Chun, Ho-Hwan;Jeon, Chung-Hwan
    • Proceedings of the KSME Conference
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    • pp.1807-1812
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    • 2004
  • Sinusoidal wavy channel is one of the most commonly used devices in the industry for achieving mixing and heat transfer. Here we report on results obtained from the DNS of flow inside the wavy channel performed using the finite volume technique. As a primary stage to obtain the optimal design for heat transfer and mixing, this study observed the basic flow structures in a wavy channel. The mass flow rate is kept constant with friction Reynolds number of $Re_{\tau}$ = 140 . Time- and space-averaged and instantaneous flow fields are illustrated to observe the flow structures. Although the direct comparison of results between turbulent wavy and flat channel is somehow difficult due to the different flow phenomena derived from different configuration, here the mean streamwise velocity and RMS of velocities at same $Re_{\tau}$ of two different channels are compared. The basic difference between wavy and flat channel flow is the existence of small scale wall vortices along the walls in a wavy channel. These vortices make flow more complex, which will accompany the increase of heat transfer, pressure drop and drag.

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Large Eddy Simulation of Turbulent Premixed Flame in Turbulent Channel Flow

  • Ko Sang-Cheol;Park Nam-Seob
    • Journal of Mechanical Science and Technology
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    • v.20 no.8
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    • pp.1240-1247
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    • 2006
  • Large eddy simulation of turbulent premixed flame in turbulent channel flow is studied by using G-equation. A flamelet model for the premixed flame is combined with a dynamic subgrid combustion model for the filtered propagation flame speed. The objective of this work is to investigate the validity of the dynamic subgrid G-equation model to a complex turbulent premixed flame. The effect of model parameters of the dynamic sub grid G-equation on the turbulent flame speed is investigated. In order to consider quenching of laminar flames on the wall, wall-quenching damping function is employed in this calculation. In the present study, a constant density turbulent channel flow is used. The calculation results are evaluated by comparing with the DNS results of Bruneaux et al.

Flow Characteristics of Drag Reducing Channel Flows Induced by Surfactant (계면활성제를 첨가한 마찰감소 채널흐름의 유동특성)

  • Park, S.R.;Yoon, H.K.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.8 no.4
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    • pp.519-526
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    • 1996
  • A 2D-LDV system was employed to investigate the flow field characteristics in fully developed drag reducing turbulent channel flows. The additive used in this study was Habon-G which showed splendid drag reduction effect and minimum mechanical degradation trend in the closed flow circulation loop. In order to have better understanding of the drag reduction mechanism, the instantaneous velocities were carefully measured under various experimental conditions and the flow characteristics including time-averaged velocity, turbulent intensity and Reynolds shear stresses were carefully assessed. The time-averaged velocity profiles of surfactant flows showed more parabolic shape(typically shown in a laminar flow) together with significant suppression of turbulent production, yielding the shear induced micelle structure orienting in the flow direction due to its isotropic characteristics. Especially it was observed that the maximum intensity for drag reducing flows was shifted away from the wall and that the streamwise and normal turbulent intensities were strongly altered. This phenomenon strongly suggests that the viscous sublayer becomes thicker with addition of surfactant. Turbulent momentum transport was drastically suppressed across the whole drag reducing channel flow.

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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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Fluid Particle Dispersion in a Turbulent Channel Flow (난류 채널 유동에서의 유체 입자 분산)

  • Choi Jung-Il;Lee Changhoon
    • Proceedings of the KSME Conference
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    • pp.803-806
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    • 2002
  • The dispersion of Lagrangian fluid particles in a turbulent channel flow is studied by a direct numerical simulation. Four points Hermite interpolation in the homogeneous direction and Chebyshev polynomials in the inhomogeneous direction is adopted by assesing the acceleration of fluid particles. In order to characterize the inhomogeneous Lagrangian statistics, accurate single particle Lagrangian statistics are obtained along the wall normal direction. Integral time scales of Lagrangian velocity can be normalized by Eulerian mean shear stresses.

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Analysis of the turbulent flow on the periodically arranged semi-circular ribs in a rectangular channel (사각채널 내 주기적으로 배열된 반원 리브 영향의 유동해석)

  • Lee, G.H.;Nine, Md.J.;Choi, S.H.;Jeong, H.M.;Chung, H.S.
    • Journal of Power System Engineering
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    • v.15 no.2
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    • pp.31-36
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    • 2011
  • The flow characteristics on the periodically arranged semi-circular ribs in a rectangular channel for turbulent flow have been investigated numerically. The aspect ratio of the rectangular channel was AR=5, the rib height to hydraulic diameter ratio was 0.07 and rib height to channel height ratio was e/H=0.117. The v2-f turbulence model and SST k-${\omega}$ turbulence model were used to find the flow characteristics of near the wall which are suited for realistic phenomena. The numerical analysis results show turbulent flow characteristics and pressure drop at the near the wall as observed experimentally. The results predict that turbulent kinetic energy(k) is closely relative to the diffusion of recirculation flow, and v2-f turbulence model simulation results have a good agreement with experimental.