Draw resonance

In film casting and fiber spinning processes, liquid material is extruded through a die with predefined speed and taken up by a rotating chill roll in order to fabricate thin films and slender fibers. The main control parameter is the so-called draw ratio, defined as the ratio of the inlet to the take-up velocity. Exceeding a critical draw ratio results in steady oscillations of both the velocity field and film or, respectively, fiber geometry, which is commonly known as draw resonance and which leads to inhomogeneous product properties and possible breakdown of the process.

The aim of these projects is to understand the influence of various effects like cooling profiles, viscoelasticity or inertia on draw resonance. For this purpose, linear stability analyses will be performed with the help of AUTO-07p, a framework for numerical continuation, as well as simulations with COMSOL.

Figure 1 Sketch of the film casting (left) and fiber spinning (right) processes. The flow direction is indicated by big arrows.

Figure 2 Visualisation of draw resonance at stable (left) and unstable (right) control parameter settings. The top plots show the film thickness over time and the bottom plots show the phase plots, all located at the middle of the streamline.

Supervisor: Mathias Bechert