法向应力差诱导黏弹性多相分层流动界面变形的机理

Mechanisms of Normal Stress Difference Induced Interfacial Distortion for Viscoelastic Multiphase Stratified Flows

通过模拟,建立了黏弹性多相分层流动的界面变形、二次流动、第二法向应力差的关联理论,提出了第二法向应力差驱动二次流动诱发界面变形的机理。结果表明,当Giesekus模型参数α由0.1增至0.45时,界面形貌由凹面向下演化为凹面向上;在侧壁区域,熔体界面的第二法向应力差均为负,如下层熔体第二法向应力差的绝对值大于上层熔体,呈向下二次流动,诱发界面向下变形,反之,则呈向上二次流动,诱发界面向上变形;上层熔体的第二法向应力差的绝对值随α的增加而增大,而下层熔体呈先增后减的抛物线分布,导致α小于0.25,二次流动为向下运动,超过0.25,演化为向上运动,必诱发界面变形的正反演化。

A relevance theory among the interfacial deformation secondary flow second normal stress difference was established by computational simulation, and the mechanisms of interfacial deformation induced by the second normal stress difference driven secondary flow was proposed. The investigation indicated that the interfacial morphology evolved from concave downward to concave upward when the Giesekus model parameter alpha increased from 0. 1 to 0.45. However, in the side wall region, the second normal stress difference of the melt along the interface became negative. If the absolute value of the second normal stress difference at the lower layer was greater than that of the upper melt, the secondary flows were all downward movement along the die wall, where a downward concave interface deformation were induced. Oppositely, the secondary flows are all upward movement along the die wall, where an upward concave interface deformation was induced. The absolute value of the second normal stress difference for the upper melt increased with an increase of alpha, whereas the melt of the lower layer increased at first and then tended to decrease. This lead to the downward movement of the secondary flow. The upward movement of the secondary flow was resulted by a value of alpha less than 0. 25. However, when alpha was greater than 0. 25, the positive and negative evolution of the interface deformation was induced definitely.