nekRS

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nekRS is an open-source Navier Stokes solver based on the spectral element method targeting classical processors and hardware accelerators like GPUs. The code started as an early fork of libParanumal tailored to our needs. For API portable programming OCCA is used.

Capabilities:

• Incompressible and low Mach-number Navier-Stokes + scalar transport
• CG-SEM using curvilinear conformal hexaheadral elements
• Adaptive 3rd/2nd order semi-implicit time integration + operator integration factor splitting
• MPI+X hybrid parallelism supporting CUDA, HIP, OPENCL and CPU
• Interface to Nek5000
• Conjugate fluid-solid heat transfer
• LES and RANS turbulence models
• ALE formulation for moving mesh support
• VisIt & Paraview support for data analysis and visualization

Build Instructions

Requirements:

• POSIX compilant OS
• GNU compiler collection version 6.2 or later
• MPI-3.1 or later
• CMake version 3.11 or later
• bash

Download the latest release tarball (recommended)

wget https://github.com/Nek5000/nekRS/archive/refs/tags/v21.1.tar.gz 
tar -zxf v21.1.tar.gz 

or clone our GitHub repository:

git clone https://github.com/Nek5000/nekRS.git

The git master branch always points to the latest release, the next branch is a special development branch that contains all the new features that will be released at the next release cycle.

To build and install the code just run:

./nrsconfig
cmake --build ./build --target install -j8

Build settings can be customized by environment variables. After installation you may want to adjust $NEKRS_HOME/nekrs.conf to your environment.

Setting the Enviroment

Assuming you run bash and your install directory is $HOME/.local/nekrs, add the following line to your $HOME/.bash_profile:

export NEKRS_HOME=$HOME/.local/nekrs
export PATH=$NEKRS_HOME/bin:$PATH

then type source $HOME/.bash_profile in the current terminal window.

Run the Code

We try hard not to break userland but the code is evolving quickly so things might change from one version to another without being backward compatible (see release notes).

cd $NEKRS_HOME/examples/turbPipePeriodic
nrsmpi turbPipe 2 # run on two MPI ranks

Note, nrsmpi/nrsbmpi are just basic launch scripts. Please check bin for more examples.

Documentation

For documentation, see our readthedocs page.

Discussion Group

Please visit GitHub Discussions. Here we help, find solutions, share ideas, and follow discussions.

Reporting Bugs

nekRS is hosted on GitHub and all bugs are reported and tracked through the Issues feature. If you are having trouble installing the code or getting your model to run properly, you should first vist our discussion group.

Contributing

Our project is hosted on GitHub and everbody is welcome to become a part of it. For more details see CONTRIBUTING.md.

License

nekRS is released under the BSD 3-clause license (see LICENSE file). All new contributions must be made under the BSD 3-clause license.

Acknowledgment

This research was supported by the Exascale Computing Project (17-SC-20-SC), a joint project of the U.S. Department of Energy's Office of Science and National Nuclear Security Administration, responsible for delivering a capable exascale ecosystem, including software, applications, and hardware technology, to support the nation's exascale computing imperative.

References

• NekRS, a GPU-Accelerated Spectral Element Navier-Stokes Solver