Flow of complex fluids
Colloidal particles immersed in a fluid interacting with the fluid and with each other.
Particles, droplets, or cells immersed in a fluid change the flowing behavior, due to hydrodynamic interactions of the objects. The fluid-structure interaction can be modeled in the simplest case with non-deformable (spherical) objects that induce an effective stress into the fluid. In a setup that is driven by a gradient flow, a corresponding stress tensor or volume force can be derived by thermodynamic considerations.
Particulate Flow
We have studied a Phase-Field Crystal model to describe the spherical particles and a Navier-Stokes equation for the description of the flow-field. A combination of both leads to simple fluid-structure intersction model for (soft) spherical particles. One question we tried to answer is where and how the particles disturb the dynamical behavior of the fluid, i.e. can dynamic barriers be broken with particles of non-zero size, like the line-barrier in a double-gyre flow.
Multiphase flow in porouse media
In printing processes an amount of liquid is applied to the surface of a paper sheet. The water based solution is intended to be absorbed by the microscopic structure of the paper. Fluid penetration is thereby driven mainly by capillary forces resulting from an interplay between surface tension and a boundary wetting angle. The forces can be controlled by varying the different coating layers on top of a fiber network that builds the core of the paper.
To simulate this process, a two-phase flow problem was formulated and implemented by means of a diffuse-interface method and Finite-Element discretization. Thereby the microscopic granular structure of the coating layers was resolved by a fine mesh. To fit the geometric structure to realistic materials, a semi-automatic mesh generator was implemented, that allows to control the granularity parameters and the structure of the capillary network. The latter is responsible for the penetration velocity and absorption time that is of fundamental interest to industrial partners.
Student projects and thesis topics
(Currently no projects)
Publications
- S. Praetorius and A. Voigt, Fluid penetration in Paper Structures, In German Success Stories in Industrial Mathematics (submitted), 2017. [bibtex]
- S. Ling, W. Marth, S. Praetorius, and A. Voigt, An adaptive finite element multi-mesh approach for interacting deformable objects in flow, In Comput. Meth. Appl. Math., Vol. 16, pp. 475–484, 2016. [doi] [bibtex]
- S. Praetorius and A. Voigt, A Navier-Stokes phase-field crystal model for colloidal suspensions, In J. Chem. Phys., Vol. 142 (15), pp. 154904, 2015. [doi] [bibtex]
- S. Praetorius and A. Voigt, A Phase Field Crystal Approach for Particles in a Flowing Solvent, In Macromol. Theor. Sim., Vol. 20 (7), pp. 541–547, 2011. [doi] [bibtex]