Paper Number
AM5                         My Program 

Session
Additive and Advanced Manufacturing of Polymers and Particles

Title
Theory of spreading viscoelastic droplets in microgravity

Presentation Date and Time
October 16, 2024 (Wednesday) 11:10

Track / Room
Track 4 / Waterloo 6

Authors (Click on name to view author profile)

1. Heitmeier, Linnea (Deutsches Zentrum für Luft- und Raumfahrt e.V., Institut für Materialphysik im Weltraum)
   Heitmeier, Linnea (Heinrich-Heine Universität Düsseldorf)
2. Voigtmann, Thomas (Deutsches Zentrum für Luft-und Raumfahrt e.V., Institut für Materialphysik im Weltraum)
   Voigtmann, Thomas (Heinrich-Heine Universität Düsseldorf)

Author and Affiliation Lines (in printed abstract book)
Linnea Heitmeier^1,2 and Thomas Voigtmann^1,2
1Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt e.V., Köln 51170, Germany; ²Heinrich-Heine Universität Düsseldorf, Düsseldorf 40225, Germany

Speaker / Presenter 
Heitmeier, Linnea

Keywords
theoretical methods; computational methods; low gravity research; non-Newtonian fluids

Text of Abstract
Viscoelastic materials share properties of an elastic solid at short response times, and that of a viscous fluid at long times. They can be characterized by long intrinsic relaxation times that separate the two behaviors.
While the spreading behavior of droplets on earth is mostly dominated by gravitational forces, the spreading behavior of droplets in microgravity is the result of an intricate balance between hydrostatic pressure, surface tension, yield stress, and the effect of shear thinning. In my talk, I will present both numerical simulations and analytical calculations regarding spreading viscoelastic droplets in microgravity.
We use a White-Metzner-type constitutive model that incorporates viscoelastic effects as well as shear-thinning and that predicts a dynamical yield stress if the viscous relaxation time goes to infinity.
For the simulation, we use a two-fluid Navier-Stokes solver to predict the droplet’s spreading behavior as well as the internal flow fields and stresses.
In the analytical calculation, we make use of the lubrication approximation to predict the droplet’s behavior. It turns out, that in the case of shear-thinning droplets, we have to make use of a different approach than for fluids without shear-thinning behavior in order to describe the spreading behavior on all timescales.
The resulting partial differential equation for the height evolution of the droplet can (in contrast to that obtained for simpler rheological models) no longer be solved analytically.
With the aid of a FEM-analysis of the analytical calculation, we can compare the analytical prediction to the simulation results.
We identify three regimes of the height evolution, related to the initial spreading, the yield-stress regime, and a final viscous-flow regime. We discuss the different time scales associated to these regimes and their crossovers.