Kármán vortex street

Problem description

The von Kármán vortex street is a very popular fluid dynamics test case. Unsteady separation of flow around blunt bodies, in this tutorial around a cylinder, causes a vortex shedding process.

Download

Mesh

For this 2 dimensional test case a Gmsh mesh file is available. Download and extract the file.

Input file

OpenCruncher uses the toml file format. Download and extract this file too.

[Hardware]
Engine = "GPU"
GPUPrecision = "Single"

[Mesh]
Name = circle.msh"

[Discretization]
TimeStepSize = 0.002
Flux = "Roe"

[Problem]
Type = "Uniform"
Ma = 0.4
Re = 100
FinalTime = 400

[BoundaryCondition-1]
Type = "Wall"

[BoundaryCondition-4]
Type = "Farfield"
Ma = 0.4

[BoundaryCondition-6]
Type = "Extrapolation"

[Output]
DisplayStep = 50
OutputStep = 500

There is no need to modify the parameter file, but if you want to run on the CPU, the parameters can be modified accordingly.

[Hardware]
Engine = "CPU"

Import the mesh

To convert the mesh into OpenCrunchers native mesh format a mesh utility is available.

x:\Cruncher\Install\bin\UtilMesh.exe circle.toml

~/Cruncher/Install/bin/UtilMesh circle.toml

After executing this command a Mesh.ocmsh file appeared.

Run OpenCruncher

The code runs on Windows or on Linux. We recommend to store and redirect the output.

x:\Cruncher\Install\bin\Cruncher.exe circle.toml > out.txt

nohup ~/Cruncher/Install/bin/Cruncher circle.toml > out.txt &
tail -f out.txt

OpenCruncher writes a bunch of transient data files until the final solution time is reached.

Post processing and evaluation

For post processing, especially of transient data, we recommend to use Paraview. Like OpenCruncher Paraview is very powerful and OpenSource.

During the solution process two Paraview compatible transient collection files (Data.pvd and SurfaceData.pvd) were written.

When playing the animation in the Paraview “Time Inspector” one can see an acoustic wave traveling outside followed by a laminar separation and finally the transient vortex street appear.