PixelFlow

Overview

This implementation is based on the papers.

This code addresses incompressible fluid dynamics using the collocated grid Marker-and-Cell (MAC) method on a Cartesian grid. Spatial discretization is performed with second-order central differencing, while temporal discretization employs a first-order explicit Euler method. For pressure calculations, the Red-Black Successive Over-Relaxation (SOR) method is implemented.

Table of Contents

• PixelFlow
  • Overview
  • Table of Contents
  • Requirements
    • Prerequisites
  • Installation
  • Getting Started
    • Setting up the Environment
    • Editing Configuration
    • Running Simulations
  • Configuring Simulations
    • &physical Section
    • &file_control Section
    • &grid_control Section
    • &porosity_control Section
    • &calculation_method Section
    • &directory_control Section
  • Running a Test Case
  • References

Requirements

To build and run this project, you will need the following tools and libraries installed on a Linux environment:

• CMake: A cross-platform build system generator.
• Make: A build automation tool.
• GCC: The GNU Compiler Collection, including the C compiler.
• G++: The GNU C++ Compiler.
• GFortran: The GNU Fortran Compiler.

Prerequisites

Make sure you have the required tools and libraries installed. You can install them using the package manager of your Linux distribution. For example, on Debian-based systems like Ubuntu, you can use apt-get:

sudo apt-get update
sudo apt-get install -y cmake make gcc g++ gfortran

Installation

1. Open a terminal and navigate to the desired working directory.

2. Clone the repository from GitHub:

   git clone https://github.com/nobu-n2002/PixelFlow.git

3. Move into the application directory:

   cd PixelFlow

4. Build all sources:

   make build

5. Create working directory:

   make project f=<your_project_name>

   The usage of make is as follows:

   Usage: make [OPTIONS]
   options
   build                    Build all source codes
   project f=<folder_name>  Create a new folder with the specified name
   help                     Display Usage

6. Check the bin Folder:

   • Upon a successful build, executable files are generated in the bin folder.

   • Open a terminal or command prompt and run the following command to verify the presence of the generated executable file(s) in the bin folder.

     ls bin

   • Ensure that the application's executable file is present in the bin folder.

7. Grant execution permissions to the executable files in the bin folder:

   chmod +x bin/*

8. Verify the config Folder:

   • Proper configuration is crucial for the application. During the build, a configuration file named controlDict.txt should be created in the config folder.

   • Open a terminal or command prompt and run the following command to confirm the existence of the controlDict.txt file in the config folder.

     cd projects/<folder_name>
     ls config

   • Confirm that the controlDict.txt file is present in the config folder.

9. Follow the steps in the Getting Started section to set up the environment and configure the simulation.

10. Proceed to the Running Simulations section to execute the simulation.

Getting Started

Setting up the Environment

1. Place the solid boundary information file (.csv) in the data/ directory.

Editing Configuration

1. Open the config/controlDict.txt file in a text editor. For detailed information on each parameter and how to configure your simulations, refer to the Configuring Simulations section.

2. Edit the variables according to your simulation requirements.

   !********************************************
   &physical
   !--- Kinematic viscosity coefficient [m2/s]
   xnue = 0.001000
   !--- Second viscosity coefficient [m2/s]
   xlambda = 0.000000
   !--- Fluid density [kg/m3]
   density = 1.000000
   !--- Domein [m]
   width   = 1.0000000
   height  = 1.0000000
   depth   = 1.0000000
   !--- Simulation time [s]
   time = 1.000000 
   ...
   !********************************************
   &solver_control
   !--- SOR max iteration steps
   iter_max        = 100
   !--- SOR reluxation factor (1<w<2)
   relux_factor    = 1.700000
   /
   !********************************************
   

3. Save the changes and close the file.

Running Simulations

1. Run the simulation script:

   make run

   You will be prompted to select an executable file. If you are using OpenMP parallelization code, please set parallel threads in config/omp_config.conf.

   Available executable files:
   0: ibm2_drag_omp
   1: ibm2_omp
   2: ibm3_air_condition_omp
   3: ibm3_omp
   Using OMP_NUM_THREADS = ${$OMP_NUM_THREADS}
   Running ibm2_omp...

2. The processes are output to runlog_*.log files inside the logs/ folder. Additionally, execution information is output to process.log inside the logs/ folder.

3. The output in the {output_folder}/ directory.

4. If you need to forcibly terminate the process during computation, please enter the following command. You will receive the process ID and a confirmation message. Input 'yes' followed by pressing enter to forcibly terminate the running process.

   make quit

Configuring Simulations

The config/controlDict.txt file contains parameters that define the properties of the simulation. Here's a breakdown of the important parameters:

&physical Section

• xnue: Kinematic viscosity of the fluid, $\nu = (\mu/\rho$) [m^2/s].
• xlambda: Second Kinematic viscosity of the fluid, ($\lambda/\rho$) [m^2/s].
• density: Density of the fluid, $\rho$ [kg/m^3].
• width, height, depth: The simulation domain, $X, Y, Z$ [m].
• time: Total simulation time, $t$ [s].
• inlet_velocity: Inlet velocity of the fluid, $U_{in}$ [m/s].
• outlet_pressure: Outlet pressure, $P_{out}$ [Pa].
• AoA: Angle of Attack, $\alpha$ [degree].

&file_control Section

• istep_out: Output interval for saving results, specified as the number of time steps.

&grid_control Section

• istep_max: Maximum number of time steps for the simulation.

&porosity_control Section

• thickness: Thickness of boundary region, $\Delta^*(=\Delta/dx$).

&calculation_method Section

• nonslip: Specify .true. for no-slip conditions or .false. for slip conditions.

&directory_control Section

• output_folder: Name of the folder where simulation results will be stored.
• csv_file: Path to the solid boundary information file in CSV format.

Adjust these parameters according to your simulation requirements. The output_folder will be created to store the simulation results, and the csv_file should point to the CSV file containing solid boundary information.

Running a Test Case

• 2D circler cylinder case

References

[1] Oshima, N., A novel approach for wall-boundary immersed flow simulation (proposal of modified Navier-Stokes equation), Journal of Fluid Science and Technology, Vol.18, No.4 (2023), https://doi.org/10.1299/jfst.2023jfst0034

[2] Oshima, N., A novel approach for wall-boundary immersed flow simulation (part 2: modeling of wall shear stress), Journal of Fluid Science and Technology, Vol.19, No.3 (2024), https://doi.org/10.1299/jfst.2024jfst0026

[3] Oshima, N., Program for flow simulation immersing wall boundary, Hokkaido university collection of scholarly and academic papers. http://hdl.handle.net/2115/89344

[4] Nakamichi, N., Cho, Y. and Oshima, N., Image-data-driven simulation of fluid dynamics (proposal and evaluation), Mechanical Engineering Journal, Vol.11, No.6 (2024), https://doi.org/10.1299/mej.24-00196

[5] Nakamichi, N., Laeron, E., Cho, Y. and Oshima, N., Moving boundary flow simulation using immersed boundary Navier–Stokes equation, The 38th Computational Fluid Dynamics Symposium (in Japanese), http://hdl.handle.net/2115/93762

[6] Nakamichi, N., Cho, Y. and Oshima, N., Fluid Simulation directly Driven by 3D image data, The 52th Visualization Symposium (in Japanese), http://hdl.handle.net/2115/93764