ABSTRACT The Molecular Stress Function (MSF) constitutive model with convective constraint release (CCR) mechanism has been shown to accurately fit a large range of viscometric data, and also shown to give strong vortex growth in flows of LDPE through planar and axisymmetric contractions. This work compares simulation and experimental results for 3-D flows of Lupolen 1840H LDPE through a contraction slit. Comparisons are made with vortex opening angles obtained from streak photography, and also with stress-birefringence measurements. The comparisons are made with two versions of the CCR mechanism. The simulated vortex angles for one version of the CCR mechanism are found to approach what is seen experimentally. The best-fit value for the stress optical coefficient was found to vary between CCRs and to decrease with flow rate. This is partially explained by different centreline elongational rates with the two CCRs, which in turn is related to different opening angles.

中文翻译：

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使用分子应力函数本构模型的 3-D 突然收缩流的实验和模拟比较

摘要 具有对流约束释放 (CCR) 机制的分子应力函数 (MSF) 本构模型已被证明可以准确地拟合大范围的粘度数据，并且还显示出通过平面和轴对称收缩在 LDPE 流中产生强烈的涡流增长。这项工作比较了 Lupolen 1840H LDPE 通过收缩缝的 3-D 流动的模拟和实验结果。与从条纹摄影获得的涡旋张角以及应力双折射测量进行比较。对 CCR 机制的两个版本进行了比较。发现一种版本的 CCR 机制的模拟涡角接近实验所见。发现应力光学系数的最佳拟合值在 CCR 之间变化并随流速降低。