OpenFOAM Axisymmetric Piston-Cylinder CFD

Minimal working example for axisymmetric piston-cylinder CFD simulations in OpenFOAM using blockMesh with transient animation capabilities.

Overview

This repository provides a complete, working example of creating axisymmetric piston-cylinder geometries in OpenFOAM using blockMesh. The case demonstrates proper wedge boundary conditions, mesh generation, steady-state and transient flow simulations, and automated animation creation.

Features

• ✅ Working axisymmetric geometry - 5° wedge angle with proper boundary conditions
• ✅ Automated setup - One-script execution from mesh to results
• ✅ Quality validated - Mesh passes OpenFOAM quality checks
• ✅ Transient simulation - Time-varying flow with animation support
• ✅ ParaView automation - Batch animation generation
• ✅ Minimal dependencies - Uses standard OpenFOAM installation
• ✅ Educational - Well-commented code for learning

Quick Start

Steady-State Simulation

```bash

Clone the repository

git clone https://github.com/your-username/openfoam-axisymmetric-piston-cfd.git cd openfoam-axisymmetric-piston-cfd

Run steady-state simulation

chmod +x runmwe.sh ./runmwe.sh

View results in ParaView

paraview case.foam ```

Transient Animation

```bash

Run transient simulation for animation

chmod +x runanimation.sh ./runanimation.sh

Generate animation (Windows with ParaView)

From PowerShell in case directory:

& "C:\Program Files\ParaView 5.13.1\bin\pvbatch.exe" animation.py ```

Geometry

The case models a simplified piston-cylinder system with: - Cylinder radius: 10 mm - Piston radius: 8 mm
- Cylinder length: 50 mm - Piston position: 20 mm from inlet - Piston length: 10 mm - Wedge angle: 5° (axisymmetric)

Requirements

• OpenFOAM (tested with v1912, should work with v5+)
• Linux/WSL environment for simulation
• ParaView for visualization (Windows version supported via WSL path)
• Git for cloning repository

File Structure

├── system/ │ ├── blockMeshDict # Mesh definition with hardcoded coordinates │ ├── controlDict # Simulation control (steady/transient modes) │ ├── fvSchemes # Numerical schemes │ └── fvSolution # Solver settings (SIMPLE/PISO) ├── constant/ │ ├── transportProperties # Fluid properties (air) │ └── turbulenceProperties # Laminar model ├── 0/ │ ├── p # Pressure field with wedge boundaries │ └── U # Velocity field with time-varying inlet ├── run_mwe.sh # Steady-state simulation script ├── run_animation.sh # Transient simulation script ├── animation.py # ParaView batch animation script └── README.md # This file

Usage

Steady-State Flow

The run_mwe.sh script performs: 1. Sets up OpenFOAM environment variables 2. Cleans previous runs (preserving initial conditions) 3. Generates mesh with blockMesh 4. Checks mesh quality with checkMesh 5. Runs steady simulation with simpleFoam 6. Creates ParaView file for visualization

Transient Animation

The run_animation.sh script performs: 1. Same setup as steady-state 2. Runs transient simulation with icoFoam 3. Creates time directories every 0.02s 4. Uses time-varying inlet velocity boundary condition

The animation.py script: - Loads OpenFOAM data in ParaView - Sets up velocity magnitude coloring - Configures camera for axisymmetric view - Exports MP4 animation (25 FPS)

Simulation Parameters

Steady-State

• Solver: simpleFoam
• Turbulence: Laminar
• Inlet: 1 m/s uniform velocity
• Outlet: Fixed pressure (0 Pa)
• Iterations: 100

Transient Animation

• Solver: icoFoam (PISO algorithm)
• Duration: 1 second
• Time step: 0.001s (for stability)
• Output: Every 0.01s (100 FPS data)
• Inlet: Time-varying velocity (0 → 0.5 → 0 m/s)

Customization

Geometry Parameters

Key parameters in system/blockMeshDict: - cr: Cylinder radius [mm] - pr: Piston radius [mm] - cl: Cylinder length [mm] - px: Piston position [mm] - pl: Piston length [mm] - ms: Mesh resolution

Boundary Conditions

Modify 0/U and 0/p for different flow conditions: - Inlet velocity profiles - Pressure boundary conditions - Wall movement (for piston motion)

Animation Settings

Adjust animation.py for different visualizations: - Color schemes (uLUT.ApplyPreset) - Camera angles - Frame rate and duration - Output format (MP4, AVI, PNG sequence)

Troubleshooting

Common Issues

Mesh generation fails: - Check OpenFOAM environment variables - Verify WM_OPTIONS is set correctly - Ensure proper file permissions

Simulation doesn't start: - Verify 0/p and 0/U files exist - Check fvSolution has required solver sections - For transient: ensure PISO section is present

Animation shows no data: - Confirm time directories were created - Check simulation completed successfully - Verify ParaView can access WSL filesystem

Numerical instability: - Reduce time step in controlDict - Lower inlet velocities in 0/U - Check Courant number in simulation log

Log Files

• blockMesh.log - Mesh generation details
• checkMesh.log - Mesh quality report
• simpleFoam.log or icoFoam.log - Simulation progress
• Check final residuals and Courant numbers

WSL + Windows ParaView Setup

This setup assumes: - OpenFOAM running in WSL (Ubuntu 22.04) - ParaView installed on Windows - Access via \\wsl.localhost\Ubuntu-22.04\... path

Example ParaView command from Windows PowerShell: powershell & "C:\Program Files\ParaView 5.13.1\bin\paraview.exe" \\wsl.localhost\Ubuntu-22.04\home\user\openfoam_cases\case\case.foam

Performance Notes

• Mesh size: 860 cells (suitable for demonstration)
• Steady simulation: ~30 seconds on typical hardware
• Transient simulation: ~1-2 minutes for 1000 time steps
• Animation generation: ~10-30 seconds depending on frames

Citation

If you use this work in your research, please cite:

bibtex @phdthesis{farimani2025, author = {Foad S. Farimani}, title = {Doctoral Dissertation}, school = {University of Twente}, year = {2025}, address = {Enschede, The Netherlands}, isbn = {978-90-365-6554-7}, doi = {10.3990/1.9789036565547}, url = {https://doi.org/10.3990/1.9789036565547} }

License

This work is licensed under CC BY-NC-SA 4.0.

Contributing

Contributions are welcome! Please feel free to submit issues or pull requests for: - Additional boundary condition examples - Improved mesh refinement strategies - Alternative solver configurations - Enhanced visualization scripts

Acknowledgments

• Developed as part of doctoral research at the University of Twente
• Based on discussions from CFD Online and Stack Overflow
• Special thanks to the OpenFOAM community for troubleshooting assistance