两种典型粘弹性流体——Giesekus流体与FENE-P流体的流变特性

The Rheological Properties of Two Typical Viscoelastic Fluids—Giesekus Fluid and FENE-P Fluid

摘要: 粘弹性流体中流动特性除了弹性(Wi)和粘性(Re)外还表现出强烈的剪切稀化特性，其所导致粘度变化对流场中流动会产生明显的影响。区别于广义牛顿流体模型，粘弹性流体模型中的粘度变化并不会直观地反应在其本构方程中，本文利用具有极小间隙的两无限大平行平板间剪切驱动流作为物理模型，定量分析与对比了两类典型粘弹性流体模型——Giesekus流体和FENE-P流体的剪切稀化特性特点与差异。研究表明：两种流体具有类似的剪切稀化趋势，当Wi低于临界值Wicr时都存在“类牛顿流体区域”，但相较于Giesekus流体，FENE-P流体的Wicr小一个量级左右。同时提出无量纲表观粘度η*，研究发现，当η*在0.3~0.7时剪切稀化效应最为剧烈。另外，本文还对FENE-P流体中分子最大拉伸长度L的取值做出了讨论。

Abstract: In addition to exhibiting elasticity (Wi) and viscosity (Re), the flow characteristics of viscoelastic fluids also show strong shear-thinning behavior, and the resulting viscosity change has a significant impact on the flow in the field. Unlike generalized Newtonian fluid models, the viscosity changes in viscoelastic fluid models are not directly reflected in their constitutive equations. Therefore, the study of viscoelastic fluid rheology is of great significance. In this article, a physical model of shear-driven flow between two infinitely parallel plates with minimal gap is used to study the shear-thinning behavior of two typical viscoelastic fluid models: Giesekus fluid and FENE-P fluid, analyzing and comparing their characteristics and differences. The results show that the two fluids exhibit a similar shear-thinning trend. When Wi is lower than the critical value Wicr, there is a “Newtonian-like fluid region” in both fluids. However, compared with Giesekus fluid, the Wicr of FENE-P fluid is about one order of magnitude smaller. Additionally, the authors proposed a dimen-sionless apparent viscosity η* and found that the shear-thinning effect is most pronounced when it is between 0.3 and 0.7 for η*. Furthermore, the maximum stretching length L of molecules in FENE-P fluid is discussed.