ISBN 9783843923477

978-3-8439-2347-7, Reihe Ingenieurwissenschaften

Eva Christiane Schlauch
Finite Element Simulations of Colloidal Aggregates in Stokes Flow

202 Seiten, Dissertation Rheinisch-Westfälische Technische Hochschule Aachen (2015), Softcover, A5

Zusammenfassung / Abstract

Solutions with colloidal aggregates fall into the category of structured fluids. This type of fluids exhibits diverse macroscopic properties that are of high interest for a large range of applications be it food processing, medical applications or the motion of coals slurries. In all those cases, the macroscopic properties depend on the microscopic structures that are formed by a large number of small objects or particles and a fluid.

The goals of this thesis are: first, to provide a simulation tool based on the in-house finite element flow solver at the Chair for Computational Analysis of Technichal Systems that allows for simulations of colloidal aggregates under Stokes flow conditions. Second, to perform calculations of steady colloidal systems and compare the results with other methods. Third, to perform simulations of rotating aggregates and evaluate the results with a second computational method.

In the course of this thesis, a partitioned fluid-structure interaction kernel for rigid-body motion is implemented based on the in-house finite element flow solver XNS. A new method is developed to allow for arbitrary three-dimensional rotations of immersed objects using a spherical shear-slip mesh layer. Care has to been taken to adjust the mesh data structure such that the parallelization of the original code is kept. Performance measurements of the method as well as mesh quality analyses are performed.

Simulations of steady flow around fixed aggregates are reported and compared with results by other methods that have been obtained in a joint effort of three work groups brought together by the priority program 1273 of the Deutsche Forschungsgemeinschaft.

In addition, a mesh-independent method to calculate particulate flows is implemented. This includes two mesh update methods and provides a means to calculate particle drag forces and torques that compares well with the standard boundary-conforming drag calculations with the benefit that the calculations are extremely cost-efficient and highly parallelizable.

The combination of the fluid-structure interaction and the mesh update enables the simulation of colloidal aggregates that rotate in a shear-flow. Results are reported for a rotating aggregate and compared with results obtained by the Stokesian dynamics method.