Transport of flexible fibers in confining micro-channels

• Applicant: Dr.-Ing. Mathias Bechert
• Subject Area: Fluid Mechanics ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403680998

This project deals with the transport of flexible micro-fibers in narrow, confining channels. In practice, this scenario is relevant for many various applications, e.g., the production of composite materials, food research or the propagation of micro-organisms in mucus.If the channel dimensions are at the same order as the fiber geometry, viscous interaction and an influence of the channel walls on the fiber dynamics will be present. In the case of stiff fibers, this manisfests in a dependence of the transport velocity on the degree of confinement, as well as an oscillating behavior of both fiber position between the lateral channel walls and orientation angle with respect to flow direction. The oscillation properties und a possible damping in particular depend hereby on the symmetry of the fiber. Therefore it could be shown that it is possible to filter asymmetric objects due to their reorientation along the middle of the channel.Up to now, the influence of elastic fiber properties has not been investigated theoretically. The possibility of bending deformation can lead to new effects, as for instance an unstable behavior, the so-called buckling, or a transport of long fibers, which would jam the channel in the case of stiff fibers. Moreover, the oscillation properties depend most likely strongly on the elastic behavior of the fiber.The challenge of a theoretical description consists in correctly considering the flow between fiber and channel walls, which makes a purely two-dimensional treatment impossible. Consequently, two modeling approaches shall be developed and evaluated in this project. One is based on an extension of a reduced two-dimensional model, the so-called Brinkman model, while the other one consists in a three-dimensional simulation and can be used additionally for validating the Brinkman model.The aim of this project is to answer the question on an appropriate modeling, as well as to investigate afterwards the dynamical behavior qualitatively and quantitatively within the experimentally relevant parameter space. The focus lies hereby on the evaluation of the results with respect to practically relevant quantities, e.g., an application dependent appropriate channel geometry.

• DFG Programme: Research Fellowships
• International Connection: Switzerland
• Host: Professor Dr. François Gallaire