• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.70-70
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• 2003

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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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.

• 대한기계학회논문집B
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• 제40권7호
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• pp.435-440
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• 2016

레이놀즈 수의 시간 증가율이 벽면난류 구조에 미치는 영향을 난류 채널유동에 대한 직접수치모사를 수행하여 조사하였다. 완전 발달된 $Re_{\tau}=180$의 난류 채널유동이 가속을 받게 되어 평균속도로 무차원화된 레이놀즈 수가 5600에서 13600까지 선형적으로 변화하게 된다. 다양한 가속 시간에 대한 계산을 수행하여 벽면난류에 대한 가속율의 효과를 파악하였다. 유량의 증가율이 큰 경우에는 우회 천이와 유사한 현상이 발견되었으며, 유량의 증가율이 낮은 경우에는 우회 천이 현상이 거의 나타나지 않았다. 본 연구 결과는 초기 레이놀즈 수와 최종 레이놀즈 수의 비 보다는 레이놀즈 수의 시간 증가율이 채널 내 과도유동에서의 우회 천이 현상 발생에 주요인자 임을 제시한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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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.

• 한국가시화정보학회지
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• 제15권3호
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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.

• Journal of Mechanical Science and Technology
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• 제20권8호
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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.

• 설비공학논문집
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• 제8권4호
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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.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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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.

• 동력기계공학회지
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• 제15권2호
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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.