Effect of the second and the third normal stress difference on occurrence of instability in viscoelastic fluid flow

本研究的目的是探讨粘弹性流体流动中法向应力差与流动失稳发生条件的关系。特别是用双光束光学测量技术测量了二维Poiseuille流体室和同心圆柱体流体室中法向应力差对流动不稳定性的影响。以表面活性剂CTAB(十六烷基三甲基溴化铵)的水溶液为试液。加入鼻塞米松(水杨酸钠)作为对抗离子。十六烷基三甲基溴化铵和鼻塞米松分别以0.23mol/L和0.03mol/L的比例溶于蒸馏水中。该样品在室温下形成蠕虫状胶束。用应变控制流变仪测试了该流体的流动特性，结果表明，该流体在低剪切速率区与单分散聚合物溶液一样，为Maxwell型线性粘弹性流体。通过使用同心圆柱体流动池，阐明了在启动流动时，…更多的S流体在一定应变下表现出流动诱导的结构变化，并在较高的剪切速率下开始流动不稳定。此外，还设计并搭建了由两块玻璃板组成的平行板流动池，用于产生二维泊松叶流。该流动池可以同时从两个方向测量流体的双折射，并且可以根据不同的实验条件改变玻璃板之间的间距。完成了流量双折射测量装置的搭建和数据采集软件的开发。当剪切速率超过3 L/S，应变超过25时，流体变得不透明。在该区域，应力-光学系数随剪切速率的变化而变化，这意味着发生了流动诱导的结构变化。第二和第三法向应力差与应力光学系数有关。因此，流动不稳定性的发生可能受这些法向应力差异的影响。具体细节还在根据本实验结果进行不断的研究。较少

The aim of this research is investigating the relation of the normal stress differences to the occurrence condition of the flow instability in viscoelastic fluid flow. Specially, the effect of the normal stress differences on the flow instability in the two-dimensional Poiseuille flow cell and the concentric cylinders flow cell was measured by the double-beams optical measurement technique. The aqueous solution of a surfactant CTAB (Cetyltrimethylammonium bromide) was used as a test fluid. NaSal (Sodium salicylate) is added as a counter ion. CTAB and NaSal were dissolved 0.23mol/l and 0.03mol/l in the distilled water. This sample forms wormlike micelles at a room temperature. The flow property of this fluid was measured by a strain-controlled rheometer and the result showed that this fluid is a Maxwell type linear viscoelastic fluid at low shear rate region as same as a mono-disperse polymer solution. It was clarified by using the concentric cylinder flow cell that at start-up flow thi … More s fluid showed the flow-induced structure change at certain strain and started the flow instability when shear rate was higher. In addition, a parallel plates flow cell made by two glass plates was designed and built up to generate two-dimensional Poiseuille flow. This flow cell is designed to measure the flow birefringence from two directions simultaneously and the space between the glass plates can be changed for various experimental conditions. The flow birefringence measurement device was finished to build and the data acquisition software was also completed. The fluid becomes opaque when shear rate and strain exceed 3 l/s and 25, respectively. In this region, the stress-optic coefficient is changed by shear rate and it means that the flow-induced structure change occurred. The second and the third normal stress differences are related with the stress-optic coefficient. So, the occurrence of the flow instability might be affected by these normal stress differences. The details are investigating by this experimental result continuously. Less