SOAPY - Simulation Of Axisymmetric Phenomena in bubblY films

Simulation Of Axisymmetric Phenomena in bubblY films

High-fidelity simulations of soap bubble dynamics and wrinkling instabilities using Basilisk C.

Research Overview

This repository contains computational tools for studying the dynamics of thin liquid films forming bubbles, with a focus on wrinkling instabilities driven by surface tension and viscous effects. The simulations solve the two-phase Navier-Stokes equations in axisymmetric configurations, capturing the complex interplay between:

• Surface tension-driven dynamics at the liquid-gas interface
• Viscous dissipation within the thin film
• Gravitational effects characterized by the Bond number
• Film thickness variations leading to instability formation

Physical System

The code models a soap bubble consisting of:

• A thin liquid film (water with surfactants)
• Surrounding gas phase (air)
• Interface dynamics tracked using Volume-of-Fluid (VOF) method
• Smoke tracer diffusion for flow visualization

Key Dimensionless Parameters

• Ohnesorge number (Oh): Ratio of viscous to inertio-capillary forces $$\text{Oh} = \frac{\mu}{\sqrt{\rho\sigma R}}$$
• Bond number (Bo): Ratio of gravitational to surface tension forces $$\text{Bo} = \frac{\rho g R^2}{\sigma}$$
• Péclet number (Pe): Ratio of advective to diffusive transport $$\text{Pe} = \frac{V_\gamma R}{D}$$ where $V_\gamma$ is the inertio-capillary velocity
• Curvature parameter (k): Ratio of bubble radius to film thickness $$k = \frac{R}{h}$$

Repository Structure

├── basilisk/src/               Core Basilisk CFD library (reference only, do not modify)
├── simulationCases/                Test cases for simulation
│   └── soapBubble-full.c           Full bubble simulation (spherical cap + rim)
│   └── soapBubble-half.c           Half-bubble simulation variant
└── postProcess/                Project-specific post-processing tools
    ├── getData.c            Data extraction utility
    ├── getFacet.c            Interface facet extraction
    └── Video-generic.py     Python script for post-processing

Simulation Configurations

Full Bubble Simulation (soapBubble-full.c)

Models a complete bubble with:

• Lower hemisphere: Circular cap geometry
• Upper region: Spherical rim structure
• Initial film thickness: $h = 1/k$
• Adaptive mesh refinement near interfaces

Half Bubble Simulation (soapBubble-half.c)

Variant configuration for studying partial bubble dynamics with modified boundary conditions.

Physical Parameters Used

Parameter	Symbol	Typical Value	Description
Ohnesorge number	$\text{Oh}$	$10^{-3}$	Viscous effects
Density ratio	$\rho_2/\rho_1$	$10^{-3}$	Gas/liquid density
Viscosity ratio	$\mu_2/\mu_1$	$10^{-3}$	Gas/liquid viscosity
Curvature parameter	$k$	25	$R/h$ ratio
Péclet number (gas)	$\text{Pe}_{\text{gas}}$	$10^{-1}$	Smoke diffusion
Domain size	$L$	5.0	Computational domain

Installation and Usage

Prerequisites

• C99-compliant compiler (gcc or clang)
• GNU make
• Python 3+ with matplotlib, numpy for post-processing

Quick Setup

# Clone repository
git clone [email protected]:comphy-lab/soapy.git
cd soapy

# Install Basilisk locally
./reset_install_requirements.sh
source .project_config

# Compile simulations
cd simulationCases
make soapBubble-full.tst

Running Simulations

# Run full bubble simulation
./soapBubble-full.tst

# Run with custom parameters (edit source file for parameter changes)
# Key parameters: Oh1, k, tmax, MAXlevel

# Output files are saved in intermediate/ directory

Post-Processing

cd postProcess

# Compile data extraction tools
qcc -autolink getData.c -o getData -lm
qcc -autolink getFacet.c -o getFacet -lm

# Generate animations
python Video-generic.py --case ../simulationCases --folder output_frames

Output Data

The simulations generate:

• Snapshot files: Binary dumps at regular intervals ($\Delta t = 0.01$)
• Interface data: VOF field and curvature information
• Velocity fields: Full velocity components in axisymmetric coordinates
• Tracer concentration: Smoke diffusion patterns
• Pressure fields: Dynamic pressure evolution

Scientific Background

The simulations investigate the Taylor-Culick instability in soap bubbles, where:

• Thin film dynamics: The bubble consists of a liquid film of thickness $h \ll R$ (bubble radius)
• Wrinkling mechanism: Instabilities arise from the competition between surface tension and viscous forces
• Rim formation: The bubble edge develops a toroidal rim structure that influences stability
• Drainage patterns: Gravity and capillary forces create complex flow patterns within the film

Relevant Physics

• Taylor-Culick velocity: Characteristic retraction speed $$V_{\text{TC}} = \sqrt{\frac{2\sigma}{\rho h}}$$
• Rayleigh-Plateau instability: Drives rim breakup and droplet formation
• Marangoni effects: Surface tension gradients due to surfactant concentration
• Film thinning: Coupled drainage and evaporation processes

Numerical Methods

The code employs:

• Volume-of-Fluid (VOF) method for interface tracking
• Adaptive mesh refinement (AMR) for resolving thin films
• Implicit viscous solver for stability at low Oh numbers
• Conservative momentum advection for accurate interface dynamics
• Height-function curvature computation for surface tension

Contributing

This code is part of ongoing research. For collaborations or questions:

• Open an issue for bug reports or feature requests
• Contact the authors for research collaborations
• See CLAUDE.md for code style guidelines

Authors

• Saumili Jana - Primary developer ([email protected])
• Vatsal Sanjay - [email protected]

License

This project is licensed under the GNU General Public License v3.0 - see the LICENSE file for details.