Flow visualization of the near-wall region in a drag-reducing channel flow
Flow visualization of the near-wall region in a drag-reducing channel flow
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DOI：
10.1017/s0022112072002514
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发表时间：
1972-12
影响因子：
3.7
通讯作者：
G. Donohue;W. G. Tiederman;M. Reischman
中科院分区：
文献类型：
--
作者：
G. Donohue;W. G. Tiederman;M. Reischman
本研究的目的是确定是否添加减阻大分子改变粘性子层的结构，从而修改湍流壁流中动能的产生。这是通过可视化充分发展的二维通道流的近壁区域来实现的。拍摄了注入近壁区域的染料的动态照片。水和稀释的减阻聚环氧乙烷-FRA溶液都用作工作流体。对运动图象进行了分析，以确定展向间距和低速条纹的破裂率，低速条纹是粘性次层的特征。减阻量的建立是从管流中的压降测量和独立于水力直径的相关性。数据表明，在减阻流中的单个条纹的爆发之间的时间具有在减小的壁面剪切下的水流的值。然而，无论是物理和无量纲条纹间距显着增加减阻流，从而空间平均爆裂率降低。这一证据有力地表明，稀聚合物溶液通过抑制低速条纹的形成来减少湍流动能的产生。这种行为是基于解决方案的高电阻拉伸应变和涡流拉伸的一个试探性的解释。
The objectives of this study were to determine whether the addition of drag-reducing macromolecules alters the structure of the viscous sublayer and thereby modifies the production of kinetic energy in turbulent wall flows. This was accomplished by visualizing the near-wall region of a fully developed two-dimensional channel flow. Motion pictures were taken of dye injected into the near-wall region. Both water and a dilute drag-reducing polyethylene oxide-FRA solution were used as working fluids. The motion pictures were analysed to determine the spanwise spacing and the bursting rate of low-speed streaks that are characteristic of the viscous sublayer. The amount of drag reduction was established from pressure-drop measurements in pipe flows and a correlation that is independent of hydraulic diameter. The data show that the time between bursts for an individual streak in a drag-reducing flow has the value for a water flow at the reduced wall shear. However, both the physical and the non-dimensional streak spacing is significantly increased in the drag-reducing flows and thus the spatially averaged bursting rate is decreased. This evidence strongly suggests that the dilute polymer solution decreases the production of turbulent kinetic energy by inhibiting the formation of low-speed streaks. A tentative explanation for this behaviour which is based upon the solution's high resistance to elongational strains and vortex stretching is offered.