Numerical and Theoretical Investigation of Gas-Film Dynamics during Droplet Impact on Liquid Films and Membrane Surfaces under High Pressures
- Institute
- Lehrstuhl für Thermodynamik (TUM-ED)
- Type
- Semester Thesis Master's Thesis
- Content
- Description
Background
When a droplet approaches a liquid or solid surface, the surrounding gas must be displaced from the narrowing gap between the droplet and the target interface. The resulting lubrication pressure deforms the interfaces and produces a thin gas film that can delay or even temporarily prevent direct contact. Although gas cushioning during droplet impact has been extensively investigated under atmospheric conditions, the influence of elevated ambient pressure remains much less understood.
Our previous experiments revealed a pronounced pressure-dependent phenomenon during droplet impact on solid/liquid interfaces: at elevated ambient pressure, the interfacial gas layer becomes significantly more pronounced and can sustain droplet–interface separation for a substantially longer period than under atmospheric conditions. This behavior can strongly affect coalescence, wetting, and mass transfer and may consequently influence practical processes such as oil–water separation.
The physical mechanisms responsible for this strong pressure dependence, however, remain unclear. In particular, the relative roles of gas density, viscosity, compressibility, lubrication pressure, interface deformation, and capillary effects need to be quantitatively resolved. This project aims to investigate the fundamental mechanisms of pressure-induced gas-film formation, drainage, and rupture during droplet impact through numerical simulations and theoretical analysis. The simulations will primarily be performed using VOF in Basilisk and/or OpenFOAM, with experimental observations providing validation and physical constraints.
Methods
The project will combine numerical simulations with theoretical scaling analysis.
The main work will include:
* Development of numerical models for droplet impact on a liquid film and/or membrane surface using Basilisk or OpenFOAM.
* Implementation of multiphase flow models capable of resolving the thin gas layer between the droplet and target interface.
* Simulation of droplet impact under atmospheric and elevated ambient pressures.
* Quantification of minimum gas-film thickness, radial gas-film profile, lubrication pressure, interface deformation, and gas-film lifetime.
* Investigation of the transition from gas cushioning to direct contact or coalescence.
* Comparison between numerical predictions and available high-pressure droplet-impact experiments.
* Development of theoretical scaling relations describing the pressure dependence of gas-film formation and drainage.
Previous Work
Previous experiments have demonstrated a pronounced pressure effect on the interfacial gas layer during droplet impact. Under elevated ambient pressure, the gas film separating the impacting droplet from the underlying interface becomes significantly more pronounced and can sustain non-contact conditions for substantially longer periods. Further details could be referred to https://doi.org/10.1002/smtd.202500913.
The present project will build upon these observations and provide the theoretical and numerical framework required to explain the experimentally observed pressure dependence.
- Requirements
* MSc student in mechanical engineering, fluid mechanics, computational engineering, applied mathematics, physics, or a related field.
* Strong interest in multiphase flow, interfacial phenomena, and computational fluid dynamics.
* Experience with CFD, numerical methods, Linux, C/C++, or Python would be advantageous.
* Previous experience with Basilisk, OpenFOAM, VOF methods, or adaptive mesh refinement would be highly beneficial but is not required.
- Possible start
- immediately
- Contact
-
M.Sc. Yan Yan
Room: 5507.EG.729
Phone: +49 89 289 16193
y.yantum.de