flowTorch - a Python library for analysis and reduced order modeling of fluid flows

flowTorch is developed primarily by the Flow Modeling and Control group led by Richard Semaan. The development is financed by the German Research Foundation (DFG) within the research program FOR 2895

unsteady flow and interaction phenomena at high speed stall conditions

with the primary goal to investigate flow conditions that lead to buffeting at airfoils in the transonic flow regime. The animation below shows the shock buffet on a NACA-0012 airfoil at Re=10^7, Ma=0.75, and 4 degrees angle of attack. The simulation was conducted in OpenFOAM; follow this link for more information about the setup.

The flowTorch project was started to make the analysis and modeling of fluid data easy and accessible to everyone. The library design intents to strike a balance between usability and flexibility. Instead of a monolithic, black-box analysis tool, the library offers modular components that allow assembling custom analysis and modeling workflows with ease. For example, performing a dynamic mode decomposition (DMD) of a transient OpenFOAM simulation looks as follows:

import torch as pt
from flowtorch import DATASETS
from flowtorch.data import FOAMDataloader, mask_box
from flowtorch.analysis.dmd import DMD

path = DATASETS["of_cylinder2D_binary"]
loader = FOAMDataloader(path)

# select a subset of the available snapshots
times = loader.write_times
window_times = [time for time in times if float(time) >= 4.0]

# load vertices, discard z-coordinate, and create a mask
vertices = loader.vertices[:, :2]
mask = mask_box(vertices, lower=[0.1, -1], upper=[0.75, 1])

# assemble the data matrix
data_matrix = pt.zeros((mask.sum().item(), len(window_times)), dtype=pt.float32)
for i, time in enumerate(window_times):
    # load the vorticity vector field, take the z-component [:, 2], and apply the mask
    data_matrix[:, i] = pt.masked_select(loader.load_snapshot("vorticity", time)[:, 2], mask)

# perform DMD
dmd = DMD(data_matrix, rank=19)
# analyse dmd.modes or dmd.eigvals
# ...

Currently, the following sub-packages are under active development. Note that some of the components are not yet available in the public release because further developments and testing are required:

flowTorch uses the PyTorch library as a backend for data structures, data types, and linear algebra operations on CPU and GPU. Some cool features of flowTorch include:

• data accessors return PyTorch tensors, which can be used directly within your favorite machine learning library, e.g., PyTorch, SkLearn or Tensorflow
• most algorithms run on CPU as well as on GPU
• mixed-precision operations (single/double); switching to single precision makes your life significantly easier when dealing with large datasets
• user-friendly Python library that integrates easily with popular tools and libraries like Jupyterlab, Matplotlib, Pandas, or Numpy
• a rich tutorial collection to help you getting started
• interfaces to common data formats like OpenFOAM, VTK (for Flexi and SU2), TAU, iPSP, CSV (for DaVis PIV data and raw OpenFOAM output)

The easiest way to install flowTorch is as follows:

# clone the repository
git clone git@github.com:AndreWeiner/flowtorch.git
# build the wheel
python3 setup.py bdist_wheel
# install flowTorch with pip
pip3 install dist/flowTorch-0.1-py3-none-any.whl
# to uninstall flowTorch, run
pip3 uninstall flowtorch

The repository contains a collection of examples as part of the documentation. To open the Jupyter labs, navigate to ./docs/source/notebooks and run jupyter lab. Note that to execute some of the notebooks, the corresponding datasets are required. The datasets can be downloaded here. Download the data into a directory of your choice and navigate into that directory. To extract the archive, run:

tar xzf datasets_20_07_2021.tar.gz

To tell flowTorch where the datasets are located, define the FLOWTORCH_DATASETS environment variable:

# add export statement to bashrc; assumes that the extracted 'datasets'
# folder is located in the current directory
echo "export FLOWTORCH_DATASETS=\"$(pwd)/datasets/\"" >> ~/.bashrc
# reload bashrc
. ~/.bashrc

For documentation and testing, the following additional packages are required:

pip3 install sphinx sphinx_rtd_theme nbsphinx pytest recommonmark

To build the HTML version of the API documentation, navigate to ./docs and run:

make html

To perform unit testing, execute pytest in the repository's top-level folder. Note that additional test data are requirement for many of the tests. There are scripts located at test/test_data to create the test data yourself. Otherwise, feel free to get in touch.

If you encounter any issues using flowTorch or if you have any questions regarding current and future development plans, please use the repository's issue tracker. Consider the following steps before and when opening a new issue:

0. Have you searched for similar issues that may have been already reported? The issue tracker has a filter function to search for keywords in open issues.
1. Click on the green New issue button in the upper right corner and describe your problem as detailed as possible. The issue should state what the problem is, what the expected behavior should be, and, maybe, suggest a solution. Note that you can also attach files or images to the issue.
2. Select a suitable label from the drop-down menu called Labels.
3. Click on the green Submit new issue button and wait for a reply.

TODO: add citeable reference

flowTorch is GPLv3-licensed; refer to the LICENSE file for more information.