OBSERVATIONS ON THE ELASTIC INSTABILITY IN CONE-AND-PLATE AND PARALLEL-PLATE FLOWS OF A POLYISOBUTYLENE BOGER FLUID
OBSERVATIONS ON THE ELASTIC INSTABILITY IN CONE-AND-PLATE AND PARALLEL-PLATE FLOWS OF A POLYISOBUTYLENE BOGER FLUID
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DOI：
10.1016/0377-0257(91)85013-9
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发表时间：
1991-09-01
影响因子：
3.1
通讯作者：
ARMSTRONG, RC
中科院分区：
文献类型：
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作者：
MCKINLEY, GH;BYARS, JA;ARMSTRONG, RC
对具有良好特性的聚异丁烯/聚丁烯溶液在锥板和平行板之间的粘性流动中剪切应力和法向应力的实验测量表明，出现了“反触变”流动转变，这导致了粘度和第一法向应力差随时间变化的明显剪切增稠。通过系统地改变平行板几何形状中的板间距，对流动转变开始的临界条件的测量表明，这种旋转不稳定性是流动中角速度的函数，并且最初随时间呈指数增长，这与Oldroyd-B模型的理论预测一致。然而，实验表明，引起这种流动转变的扰动是非轴对称的，在时间上是超稳定的，在伽马曲线上是亚临界的。频谱分析还表明，最终发展的非线性流动在时间上是非周期的。这些流动转变的特征与已有的理论分析不符。实验建立的流动稳定性图表明，对于给定的流体，不稳定发生在临界Deborah数处，该临界Deborah数对流动的特定几何参数、温度和剪切速率不敏感。这种对弹性不稳定性的解释澄清了最近对M1粘弹性测试流体流动稳定性的测量。
Experimental measurements of the shear stress and normal stresses in the viscometric flow of a well-characterized polyisobutylene/polybutene solution between a cone-and-plate and between parallel plates show the onset of an "anti-thixotropic" flow transition, which results in a time-dependent, apparent shear-thickening of the viscosity and first normal stress difference. Measurements of the critical conditions for the onset of the flow transition, made by systematically varying the plate separation in the parallel-plate geometry, demonstrate that this rotational instability is a function of the angular velocity in the flow and initially grows exponentially in time, in agreement with theoretical predictions for an Oldroyd-B model. However, experiments show that the disturbance which causes this flow transition is nonaxisymmetric, over-stable in time and subcritical in gamma. Spectral analysis also shows that the nonlinear flow which ultimately develops is temporally aperiodic. These features of the flow transition do not agree with the existing theoretical analysis. The experimentally constructed flow-stability diagram shows that, for a given fluid, the instability occurs at a critical Deborah number which is insensitive to the specific geometrical parameters, temperature, and shear-rate of the flow. This interpretation of the elastic instability clarifies recent measurements of the flow stability for the M1 viscoelastic test fluid.