NASA Glenn Research Center
Wetting Stability and Instabilities and Very High Capillary Number Coating
Wetting phenomena are important in industrial coating, in oil extraction and in hydrology. Wetting is a form of molecular bonding. This takes place at the nano-scale and the details of it vary considerably depending on the wetting liquid and the solid being wetted. Nevertheless, the visible hydrodynamics of wetting can often be approximately predicted by the Navier-Stokes equations supplemented by slip-length models for the flow against the solid and/or diffuse interface (phase-field) thermodynamically-based models of the meniscus. These models eliminate an apparent singularity at the wetting line and the phase-field model also captures the gross energetics of wetting.
This talk will discuss surface-tension-driven flows with an emphasis on wetting and coating. I will be presenting a mix of theory and numerical simulations. Methods for calculating wetting flows using phase-field models will be briefly described and some two- and three-dimensional phase-field-Navier-Stokes calculations of surface-tension-driven flows will be shown. On the theoretical side I will discuss optical fiber coating and how to wet/coat without bubble formation at very high capillary numbers (O(1000)). I will also discuss wetting flow instabilities, including my attempts to understand and calculate the onset of corrugations at wetting lines and their development into the sawtooth instability.