Flow visualization and skin friction determination in transitional channel flow
Flow visualization and skin friction determination in transitional channel flow
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过渡通道流动中的流动可视化和表面摩擦力测定
DOI：
10.1007/s00348-020-03102-6
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发表时间：
2021
影响因子：
2.4
通讯作者：
M.
中科院分区：
文献类型：
--
作者：
Yimprasert;S.;Kvick;M.;Alfredsson;P.H.;Matsubara;M.
摘要本文通过实验确定了平面通道流动的过渡雷诺数范围，并对其过渡状态进行了表征。测量沿通道的压力，以确定表面摩擦系数作为雷诺数的函数，从层流状态，通过过渡区域进入完全湍流状态。通过流动可视化对流动结构进行了研究，结果表明，随着雷诺数从层流状态增加，过渡区开始出现随机出现的湍流点。随着雷诺数的增加，黑点转变为斜斑块和小尺度湍流带，形成横跨通道宽度的小尺度湍流带，以及在湍流区域之间的区域发现的大规模条纹结构。利用图像分析技术确定了间歇系数，即流动中的湍流率作为雷诺数的函数。发现表面摩擦系数在流动完全紊流之前达到其紊流值（间歇系数仍小于1）。这表明在非湍流区域观察到的条纹结构有助于增强动量的壁法向转移。在紊流表面摩擦系数已建立的雷诺数以上，还发现了不规则条纹结构构成的大规模特征。它们具有与过渡流中的非湍流斑块和湍流斑块相似的倾斜形状，表明即使在表面摩擦达到湍流水平的雷诺数以上，过渡过程也没有完全完成。图形抽象对流动可视化图像进行处理，以确定过渡区域的湍流间歇性。流程图从左到右，(a)未处理，(b)滤波后(c) (b)标准差，(d)二值图
AbstractThe present study experimentally determines the transitional Reynolds number range for plane channel flow and characterizes its transitional state. The pressure along the channel is measured to determine the skin friction coefficient as function of Reynolds number from the laminar state, through the transitional region into the fully turbulent state. The flow structure was studied through flow visualisation which shows that as the Reynolds number increases from the laminar state the transitional region starts showing randomly occurring turbulent spots. With increasing Reynolds number the spots shift into oblique patches and bands of small scale turbulence that form across the channel width, together with large-scale streaky structures found in areas between the turbulent regions. An image analysing technique was used to determine the intermittency factor, i.e. the turbulence fraction in the flow, as function of Reynolds number. It is found that the skin friction coefficient reaches its turbulent value before the flow is fully turbulent (the intermittency factor is still below one). This suggests that the observed streaky structures in non-turbulent regions contribute to the enhancement of the wall-normal transfer of momentum. Also above the Reynolds numbers where the turbulent skin friction coefficient has been established large-scale features consisting of irregular streaky structures are found. They have an oblique shape similar to the non-turbulent and turbulent patches in the transitional flow indicating that the transition process is not fully complete even above the Reynolds number where the skin friction reaches its turbulent level.Graphic abstractProcessing of flow visualization images to determine the turbulence intermittency in the transitional region. Flow is from left to right, (a) unprocessed, (b) filtered (c) standard deviation of (b), (d) binary picture
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影响因子：
1.5
作者：
E. Zanoun;H. Nagib;F. Durst
通讯作者：
E. Zanoun;H. Nagib;F. Durst
影响因子：
2.4
作者：
Durst, F;Kikura, H;Ye, Q
通讯作者：
Ye, Q
第1222章 纳米原纤化纤维素悬浮液对过渡二维通道流的影响
DOI：
10.1299/jsmeicjwsf.2013.4._1222-1_
发表时间：
2013
期刊：
--
影响因子：
--
作者：
Matsubara Masaharu;Miyazaki Makoto;Watanabe Kenta;Kvick Mathias;L. Fredrik;S. Daniel
通讯作者：
S. Daniel
DOI：
10.1016/j.ijheatfluidflow.2016.11.009
发表时间：
2016
影响因子：
2.6
作者：
M. Matsubara;Shun Horii;Y. Sagawa;Y. Takahashi;Daisuke Saito
通讯作者：
Daisuke Saito
影响因子：
4.6
作者：
Schultz, M. P.;Flack, K. A.
通讯作者：
Flack, K. A.