• Title/Summary/Keyword: Turbulent channel flow

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Characteristics of Accelerations in Turbulent Channel Flow (난류 채널 유동에서의 가속도 특성)

  • Yeo, Kyong-Min;Lee, Chang-Hoon
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1801-1805
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    • 2003
  • The intermittent characteristics of fluid particle accelerations near the wall are investigated with the higher-order statistics and the probability density functions (PDF) by using a direct numerical simulation of turbulent channel flow. Also, the behaviors of acceleration associated with the coherent structures are discussed. The flatness factor of wall-normal acceleration is extremely high near the wall and it exceeds the previously reported value obtained in isotropic turbulence. The presence of the wall seems to make the accelerations more intermittent and the associated mechanism is explained with the PDFs. The skewness factor of wall-normal acceleration indicates that accelerations are associated with the streamwise vortices.

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Lagrangian Investigation of Turbulent Channel Flow (I) - An Assessment of Particle Tracking Algorithms - (난류채널유동의 라그란지안 해석 (I)- 입자추적 알고리듬 평가 -)

  • Choi, Jung-Il;Lee, Chang-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.7
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    • pp.859-866
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    • 2003
  • The Lagrangian dispserion of fluid particles in inhomogeneous turbulence is investigated by a direct numerical simulation of turbulent channel flow. Fluid particle velocity and acceleration along a particle trajectory are computed by employing several interpolation schemes such as linear interpolation, high-order Lagrange polynomial interpolation and the Hermite interpolation schemes. The performances of the schemes are evaluated through comparison of errors in computed particle positions, velocities and accelerations against spectral interpolation. Adopting the four-point Hermite interpolation in the homogeneous directions and Chebyshev polynomials in the wall-normal direction appears to produce most reliable Lagrangian statistics including acceleration correlations with a reasonable amount of computational overhead.

The Distribution of Chironomids by Flow Mechanisms - Artificial Channel Measurement - (흐름 메카니즘에 의한 깔따구들의 분포(I) - 인공수로 실험 -)

  • Lee, Sang-Ho;Lee, Jung-Min;Park, Jae-Hyun;Song, Mi-Young
    • Journal of Korean Society on Water Environment
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    • v.22 no.1
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    • pp.150-158
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    • 2006
  • Over the past few years, many studies have been conducted on the flow, sediment movement, pollution transportation and scour etc. However, very few attempts have been made at the hydraulic studies reflecting upon the ecological function. The objective of this study is to examine the structures of the flow and turbulence in an open circular channel and their relationship to distribution of the organisms and chironomids. Under different flow conditions, the organic matter and some chironomids were injected into the channel. Using the obtained velocity data, the flow mechanisms and the turbulent shear stresses were analyzed. Organic matters and chironomids were distributed on the region that the velocity was slower and the turbulent shear stresses were smaller. Some habitat moved even though chironomids were inhabited. This phenomenon has relationship with the flow mechanism. Some chironomids have distributed around the habitat structure of a hemisphere. The secondary flow has affected the deposition of the organic matters and the distribution of chironomids.

An Experimental Study on the Depth Variation of Water Flow on Steep Open Channel with Constant Width (一定幅 急傾斜 開水路上을 流動하는 물의 깊이 變化에 관한 實驗的 硏究)

  • 박이동
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.1
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    • pp.86-95
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    • 1986
  • A study on film water flow on steep open channel has been seldom found up to date. Therefore, this paper dealed with the depth variation of film thickness of water (city supply normal water) flowing on steep open channel. For this purpose, Experimental apparatus (made of a normal glass with 160cm of length and 15cm of width) was made and the depths of the water flowing on the channel were measured experimentally, changing the channel slope angle from 30 to 80 degree (5 steps) and the flow rate from 0.25 to 10CPM (11 steps). The results obtained, some characteristics of the film flow on the channel are as follows. (1) When thin film water flowed on steep open channel, the depths of flow tended to increase after decreasing and was kept nearly constant in its downstream in case of laminar and transitional flow region. The turining point of the depths of flow from decrease to increase tended to move downward with the increase of Reynolds number. In turbulent flow region, the depths of flow showed reapid decrease in its upper stream, gradual decrease in its midstream and were kept nearly constant in its downstream. (2) While the differences between the depths of flow along the channel slope got small in its upper stream and got large in its downstream in case of laminar flow region, they got very large in its upper stream and were kept nearly constant in its downstream in case of transitional and turbulent flow region. And the move flow rate increases, the more the differences between the depths of flow along the channel slope got large in its upper stream.

Large eddy simulation of turbulent flow around a wall-mounted cubic obstacle in a channel using Lagrangian dynamic SGS model (Lagrangian Dynamic Sub-grid Scale 모델에 의한 평행평판내 입방체 장애물 주위 유동에 관한 대 와동 모사)

  • Ko, Sang-Cheol;Park, Nam-Seob
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.3
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    • pp.369-375
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    • 2006
  • Large eddy simulation has been applied to simulate turbulent flow around a cubic obstacle mounted on a channel surface for a Reynolds number of 40000(based on the incoming bulk velocity and the obstacle height) using a Smagorinsky model and a Lagrangian dynamic model. In order to develop the LES to the practical engineering application, the effect of upwind scheme, turbulent sub-grid scale model were investigated. The computed velocities. turbulence quantifies, separation and reattachment length were evaluated by compared with the previous experimental results.

Experimental Study on Frictional Drag Reduction of Turbulent Flow by Polymer Solution Injection (폴리머 수용액 주입에 의한 난류마찰저항 감소에 대한 실험 연구)

  • 김형태;김덕수;김우전
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.3
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    • pp.9-15
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    • 2003
  • An experimental study has been carried out as a basic research for development of the friction drag reduction technology for ships by polymer injection. Experimental apparatus and procedures have been devised and prepared to measure the changes of the wall friction with injection of a polymer solution and basic experimental data on the friction drag reduction are obtained for a turbulent fiat-plate boundary layer and fully-developed channel flows. Variations of the friction drag reduction with some important parameters of polymer injection, such as the concentration of polymer solution, its injection flow rate and the measuring position downstream from the injection slot, are also investigated. Important experimental data and results obtained in the present study are presented. The amount of friction drag reduction up to 50% is observed.

Turbulent Flow over Thin Rectangular Riblets

  • El-Samni O. A.;Yoon Hyun Sik;Chun Ho Hwan
    • Journal of Mechanical Science and Technology
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    • v.19 no.9
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    • pp.1801-1810
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    • 2005
  • The effect of longitudinal thin rectangular riblets aligned with the flow direction on turbulent channel flow has been investigated using direct numerical simulation. The thin riblets have been modeled using the immersed boundary method (IBM) where the velocities at only one set of vertical nodes at the riblets positions are enforced to be zeros. Different spacings, ranging between 11 and 43 wall units, have been simulated aiming at getting the optimum spacing corresponding to the maximum drag reduction while keeping the height/spacing ratio at 0.5. Reynolds number based on the friction velocity ${\mu}_\tau$ and the channel half depth $\delta$ is set to 150. The flow is driven by adjusted pressure gradient so that the mass flow rate is kept constant in all the simulations. This study shows similar trend of the drag ratio to that of the experiments at the different spacings. Also, this research provides an optimum spacing of around 17 wall units leading to maximum drag reduction as experimental data. Explanation of drag increasing/decreasing mechanism is highlighted.

Large Eddy Simulation of Turbulent Channel Flow Using Inhomogeneous Filter (비균질 필터를 사용한 난류 채널 유동의 Large Eddy Simulation)

  • Lee, Sang-Hwan;Kim, Kwang-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.9
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    • pp.1022-1031
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    • 2004
  • The commutation errors by the filtering process in the large eddy simulation are considered. It is compared the conventional filter with the inhomogeneous filter that is devised to reduce the commutation errors. The weighting factor of the inhomogeneous filter suggested by Vasilyev is adopted. Also, using the optimizing function that estimates test filter width to eliminate the dissipations in the region excluding the vicinity of the wall, the flow patterns are analyzed. It is evaluated in simulations of the turbulent channel flow at Reynolds number of 1020, based on friction velocity and channel half height. Results show that the commutation errors can be significantly reduced by using the inhomogeneous filter and the optimized test filter width.

NUMERICAL STUDIES ON FLOWS WITH STRONG PROPERTY VARIATIONS THROUGH STRAIGHT RECTANGULAR CHANNELS (곧은 사각채널을 통과하는 물성 변화가 큰 유동에 대한 수치해석)

  • Choi, Nam-Jung;Choi, Yun-Ho
    • Journal of computational fluids engineering
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    • v.12 no.4
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    • pp.74-84
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    • 2007
  • The flowfield characteristics in a straight rectangular channel have been investigated through a numerical model to analyze the regenerative cooling system that is used in rocket engine cooling. The supercritical hydrogen coolant introduces strong property variations that have a major influence on the developing flow and heat transfer characteristics. Of particular interest is the improved understanding of the physical characteristics of such flows through parametric studies. The approach used is a numerical solution of the full Navier-Stokes equations in the three dimensional form including the arbitrary equation of state and property variations. The present study compares constant and variable property solutions for both laminar and turbulent flow. For laminar flow, the variation of aspect ratio is examined, while for turbulent flow, the effects of variation of channel length and Reynolds number are discussed.

Flow Visualization of Turbulent Flow around a Sphere (구(球) 주위 난류유동의 정량적 가시화)

  • Jang, Young-Il;Lee, Sang-Joon
    • 한국가시화정보학회:학술대회논문집
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    • 2005.12a
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    • pp.50-53
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    • 2005
  • The turbulent flow around a sphere was investigated in a streamwise meridian plane using two experimental techniques: smoke-wire flow visualization in wind tunnel at Re=5,300 and PIV measurements in a circulating water channel at Re=7,400. The smoke-wire visualization shows flow separation points near an azimuthal angle of $90^{\circ}$, recirculating flow, transition from laminar to turbulent shear layer, evolving vortex roll-up and fully turbulent eddies in the sphere wake. In addition, the mean flow pattern extracted by particle tracing method in water tunnel at Re= 14,500 reveals two distinct comparable toroidal(not closed) vortices in the recirculation region. The mean velocity field measured using a PIV technique demonstrates the detailed wake configuration of close symmetric recirculation and near-wake configuration with two toroidal vortices, reversed velocity zone and vorticity contours.

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