Fakhari Ahmad, Tukovic Željko, Carneiro Olga Sousa, Fernandes Célio
Institute for Polymers and Composites, Department of Polymer Engineering, Campus of Azurém, University of Minho, 4800-058 Guimarães, Portugal.
Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Ivana Lučića 5, 10000 Zagreb, Croatia.
Polymers (Basel). 2021 Apr 16;13(8):1305. doi: 10.3390/polym13081305.
The extrudate swell, i.e., the geometrical modifications that take place when the flowing material leaves the confined flow inside a channel and moves freely without the restrictions that are promoted by the walls, is a relevant phenomenon in several polymer processing techniques. For instance, in profile extrusion, the extrudate cross-section is subjected to a number of distortions that are motivated by the swell, which are very difficult to anticipate, especially for complex geometries. As happens in many industrial processes, numerical modelling might provide useful information to support design tasks, i.e., to allow for identifying the best strategy to compensate the changes promoted by the extrudate swell. This study reports the development of an improved interface tracking algorithm that employs the least-squares volume-to-point interpolation method for the grid movement. The formulation is enriched further with the consistent second-order time-accurate non-iterative Pressure-Implicit with Splitting of Operators (PISO) algorithm, which allows for efficiently simulating free-surface flows. The accuracy and robustness of the proposed solver is illustrated through the simulation of the steady planar and asymmetric extrudate swell flows of Newtonian fluids. The role of inertia on the extrudate swell is studied, and the results that are obtained with the newly improved solver show good agreement with reference data that are found in the scientific literature.
挤出胀大是指流动材料离开通道内的受限流动并在没有壁面所施加限制的情况下自由移动时发生的几何形状变化，这是几种聚合物加工技术中的一个相关现象。例如，在型材挤出中，挤出物横截面会因胀大而出现多种难以预测的变形，对于复杂几何形状尤其如此。正如许多工业过程中那样，数值模拟可为设计任务提供有用信息，即有助于确定补偿挤出胀大所引起变化的最佳策略。本研究报告了一种改进的界面跟踪算法的开发，该算法采用最小二乘体积到点插值方法进行网格移动。该公式进一步采用了一致的二阶时间精确非迭代算子分裂压力隐式（PISO）算法，该算法能够有效模拟自由表面流动。通过对牛顿流体的稳态平面和非对称挤出胀大流动进行模拟，展示了所提出求解器的准确性和鲁棒性。研究了惯性对挤出胀大的作用，新改进求解器获得的结果与科学文献中的参考数据显示出良好的一致性。
