Research Initiation: Stability Analysis of Interfaces in Coextrusion Flows

该研究的目的是确定与共挤过程相关的构型中多层内部流动的稳定性特征。主要的兴趣是研究非平行通道壁对两种不稳定机制的影响：与流体-流体界面的存在相关的机制和与固体壁的存在相关的机制。所要研究的基线几何是由两个由汇聚段连接的等宽断面组成的二维航道。采用局部线性分析、全局线性分析和直接数值模拟的方法，考察了三层不同粘度和密度的牛顿流体稳态等温流动的稳定性。直接数值模拟将基于谱离散(谱元)全非定常Navier-Stokes方程的时间精确积分。这项研究将扩展到非牛顿流体，并将包括热效应。该项目的长期目标是开发一种可靠的方法，用于(1)预测共挤过程的稳定性特征和(2)共挤模具的设计测试和分析。这项研究将有助于改进聚合物共挤出的制造工艺。

The objective of the research is to determine the stability characteristics of multi-layer internal flows in configurations relevant to coextrusion processes. The primary interest is to study the effect of non-parallel channel walls on the two mechanisms for instability: the mechanism associated with the presence of fluid-fluid interfaces and the mechanism associated with the presence of solid walls. The baseline geometry to be studied is a two-dimensional channel consisting of two constant width sections joined by a converging section. The stability of steady isothermal flow of three layers of Newtonian fluids of different viscosities and densities will be examined using local linear analysis, global linear analysis, and direct numerical simulation. The direct numerical simulation will be based on time- accurate integration of the spectrally discretized (spectral elements) full unsteady Navier-Stokes equation. The study will be extended to non-Newtonian fluids and will incorporate thermal effects. The long term goal of the project is the development of a reliable method for the (1) prediction of stability characteristics of coextrusion processes and (2) design testing, and analysis of coextrusion dies. The research will lead to improved manufacturing process for coextrusion of polymers.