Mesh immersion technique for 3D moving domain calculation and applications to twin-screw extrusion and mixing

Abstract

International audienceThis work is concerned with the development of numerical techniques devoted to the simulation of the flow of a polymer melt in mixing processes such as twin-screw extrusion. In mixing or twin extrusion process simulation, the absence of symmetry of the moving boundaries (the screws) implies that their rigid body motion has to be taken into account by using a special treatment. In this study, we introduce a new technique called Mesh Immersion Technique (MIT), which consists in : a) using a P1+/P1-based (MINI-element) mixed finite element method for solving the velocity-pressure problem, b) solving the problem in the whole barrel cavity and imposing a rigid motion (rotation) to nodes found located inside the so called immersed domains. Each sub-domain (screw) is represented by a surface mesh. The independent meshes are immersed into a unique background computational mesh by calculating the P1 approximation of the function giving the distance to their respective surfaces. A multiphase approach, combined with parallel computing, is used to compute the flow of generalized Newtonian fluids in a complex system such as a twin screw extruder or a batch mixer, including moving free surfaces