Nonlinear dynamics of viscoelastic flow in axisymmetric abrupt contractions
Nonlinear dynamics of viscoelastic flow in axisymmetric abrupt contractions
复制标题
轴对称突然收缩中粘弹性流的非线性动力学
DOI：
10.1017/s0022112091001489
复制
发表时间：
1991
影响因子：
3.7
通讯作者：
R. Armstrong
中科院分区：
文献类型：
--
作者：
G. McKinley;William P. Raiford;Robert A. Brown;R. Armstrong
通过激光多普勒测速和流动可视化测量的Deborah数和收缩比，在一个良好的特征粘弹性流体流动通过突然的轴对称收缩观察到的稳态和随时间变化的流动转变的特点。确定了一系列的流动转变，导致时间周期性，准周期性和非周期性的收缩唇附近的动态和唇入口处的弹性涡流的形成。随着Deborah数的增加，该唇缘涡的强度增加并向外扩展到上游管中，直到进一步的流动不稳定性导致大弹性涡的不稳定振荡。这些转变的临界德博拉数的值取决于收缩比β，定义为大小管的半径之比。仅在收缩比为2 [les ] β [les ] 5时观察到收缩唇附近的时间依赖性三维流动，并且在更高的收缩比下流动保持稳定。圆角的4：1突然收缩的角导致这些流转变的开始的Deborah数的值增加，但不改变转变的一般结构。
The steady-state and time-dependent flow transitions observed in a well-characterized viscoelastic fluid flowing through an abrupt axisymmetric contraction are characterized in terms of the Deborah number and contraction ratio by laser-Doppler velocimetry and flow visualization measurements. A sequence of flow transitions are identified that lead to time-periodic, quasi-periodic and aperiodic dynamics near the lip of the contraction and to the formation of an elastic vortex at the lip entrance. This lip vortex increases in intensity and expands outwards into the upstream tube as the Deborah number is increased, until a further flow instability leads to unsteady oscillations of the large elastic vortex. The values of the critical Deborah number for the onset of each of these transitions depends on the contraction ratio β, defined as the ratio of the radii of the large and small tubes. Time-dependent, three-dimensional flow near the contraction lip is observed only for contraction ratios 2 [les ] β [les ] 5, and the flow remains steady for higher contraction ratios. Rounding the corner of the 4:1 abrupt contraction leads to increased values of Deborah number for the onset of these flow transitions, but does not change the general structure of the transitions.