粘塑性流体在同轴环空域内的流动特性及稳定性机理研究

This project studies the flow characteristics and stability mechanism of co-axial annular flow of viscoplastic fluids. Co-axial annular flows are usually driven by the axial translation as well as circumferential rotation of inner/outer cylinders with imposed axial pressure gradient. Due to the complexity of this problem, studies on flow characteristics and stability mechanism of co-axial annular flow of viscoplastic fluids are heretofore limited to considerations of one or two driving factors. However, in the practical application of oil well drilling, drilling fluid flow is generated by the spiral motion of drill rod and imposed pressure gradient, which implies the influences of coexistence of three driving factors on flow characteristics and hydrodynamics stability need to be clarified. In this project, we employ two viscoplastic fluid models (Bingham fluid model and Herschel-Bulkley fluid model) to study the co-axial annular flow characteristics under three driving factors. Corresponding methods of numerical computation and modal/non-modal stability analysis are developed to explore the physical mechanism of flow instability. We emphasize on the influence of yield stress on flow stability. As this kind of flow is widely encountered in industrial productions such as oil well drilling and polymer extrusion, this project not only has important theoretical significance on the explorations of flow instability mechanism of non-Newtonian fluids, but also has certain potential application background.

本项目研究粘塑性流体在同轴圆筒间环形空间（以下简称“环空”）域内的流动特性和稳定性机理。环空域内的流动通常由筒壁的轴向运动、周向转动以及轴向压力梯度三种因素所驱动。由于问题的复杂性，迄今为止，粘塑性流体环空域内的流动特性和稳定性研究还仅限于一到两种驱动因素存在的情况。而在实际的石油钻井中，钻井液受压力梯度驱动，同时钻杆沿轴向螺旋前进，需要阐明三种驱动因素共存对环空域内粘塑性流体流动特性及稳定性的影响。在本项研究中，我们将采用Bingham、Herschel-Bulkley两种粘塑性流体模型，研究三种驱动因素共存的环空域内流动特性，通过发展相应的数值计算和模态/非模态稳定性分析方法，探索流动失稳的物理机制，重点阐明屈服应力对流动稳定性的影响。由于此类流动在石油钻井、聚合物挤出成型等工业生产中广泛存在，故该项研究不但对探索非牛顿流稳定性机理具有重要的理论意义，同时也有一定的潜在应用背景。

本项目主要研究粘塑性流体在同轴圆筒间环形空间（以下简称“环空”）域内的流动特性和稳定性机理。环空域内的流动通常由筒壁的轴向运动、周向转动以及轴向压力梯度三种因素所驱动。由于问题的复杂性，迄今为止，粘塑性流体环空域内的流动特性和稳定性研究还仅限于一到两种驱动因素存在的情况。而在实际的石油钻井中，钻井液受压力梯度驱动，同时钻杆沿轴向螺旋前进，需要阐明三种驱动因素共存对环空域内粘塑性流体流动特性及稳定性的影响。在本项研究中，我们采用适当的粘塑性流体模型，研究三种驱动因素共存的环空域内流动特性，通过发展相应的数值计算和模态/非模态稳定性分析方法，探索流动失稳的物理机制，重点阐明屈服应力和剪切稀化效应等对流动特性和流动稳定性的影响。研究结果表明：1）宾汉流体环空螺旋流除了同样具有轴向库埃特-泊肃叶流的八种流动型态，还多了两种新的流动型态，并分析了这种新的流动型态的具体情况和出现的原因；2）在滑移边界条件下，粘塑性流体的环空流动会受到显著影响，各种流动型态的分布区域也会发生显著变化；3）在对均匀横流下 Carreau 流体（粘塑性流体模型之一）平面Couette-Poiseuille 流动的稳定性研究中，发现剪切稀化改变基本流的稳定作用和附加粘性项的失稳作用在这里产生了竞争，即剪切稀化特性对流动稳定性有双重作用。由于此类流动在石油钻井、聚合物挤出成型等工业生产中广泛存在，故该项研究不但对探索非牛顿流稳定性机理具有重要的理论意义，同时也有一定的潜在应用背景。