My second tutorial: cylinderInChannel

Tutorial Aims

• Demonstrate how to perform a fluid-only analysis in solids4foam;
• Explain how a solids4foam fluid case differs from a standard OpenFOAM fluid case.

Case Overview

This is the classic "flow over a cylinder in a channel" test case, as analysed by, for example, Ferziger and Peric (2002). The problem is modelled as 2-D. The inlet flow velocity profile is specified (coming in from the left), and the outlet (right) gauge pressure is zero. The upper wall, lower wall and cylinder are no-slip walls.

We assume an incompressible Newtonian isothermal laminar fluid, where the Navier-Stokes governing equations take the form:

We will use the PIMPLE pressure-velocity coupling algorithm:

for all time-steps
    do
        solve momentum equation for U (terms depending on p are calculated explicitly)
        solve pressure equation for p (terms depending on U are calculated explicitly)
    while not converged
end

Expected Results

For Re = 100, the flow is expected to be unsteady, with vortices shedding from the cylinder.

Running the Case

The tutorial case can be run using the included Allrun script, i.e. > ./Allrun. In this case, the Allrun script is

#!/bin/bash

# Source tutorial clean functions
. $WM_PROJECT_DIR/bin/tools/RunFunctions

# Source solids4Foam scripts
source solids4FoamScripts.sh

# Check case version is correct
solids4Foam::convertCaseFormat .

# Create the mesh
solids4Foam::runApplication fluentMeshToFoam cylinderInChannel.msh
solids4Foam::runApplication changeDictionary

# Run the solver
solids4Foam::runApplication solids4Foam

# Create plots
if command -v gnuplot &> /dev/null
then
    if [[ -f "./postProcessing/forces/0/forces.dat" ]]
    then
        echo "Generating force.pdf using gnuplot"
        gnuplot force.of9.gnuplot &> /dev/null
    else
        echo "Generating force.pdf using gnuplot"
        gnuplot force.gnuplot &> /dev/null
    fi
else
    echo "Please install gnuplot if you would like to generate the plots"
fi

where the solids4Foam::convertCaseFormat . script makes minor changes to the case to make it compatible with your version of OpenFOAM/foam-extend. As can be seen, the mesh in the fluent format is converted to the OpenFOAM format before running the solids4Foam solver. After the solver has finished, a force.pdf plot is generated if the gnuplot program is installed.

Analysing the Results

In the ParaView, a von Kármán vortex street is clearly visible by viewing the pressure field p:

Delving Deeper

If you would like to learn more about the case, then please continue; if not, how about you check out another tutorial.

Case Structure

The case follows the typical pimpleFoam (or pimpleDyMFoam) case structure:

cylinderInChannel
├── 0
│   ├── U
│   └── p
├── Allclean
├── Allrun
├── constant
│   ├── RASProperties
│   ├── dynamicMeshDict
│   ├── fluidProperties
│   ├── physicsProperties
│   ├── polyMesh
│   │   └── …
│   ├── transportProperties
│   └── turbulenceProperties
├── cylinderInChannel.msh
└── system
    ├── changeDictionaryDict
    ├── controlDict
    ├── fvSchemes
    └── fvSolution

The only difference with a pimpleFoam case is that a constant/physicsProperties dictionary must be present, where the type of analysis is specified:

type     fluid;
//type   solid;
//type   fluidSolidInteraction;

In addition, as this is a "fluid" analysis, a constant/fluidProperties dictionary must also be present, where the PIMPLE algorithm for an incompressible isothermal fluid is specified:

fluidModel pimpleFluid;

pimpleFluidCoeffs
{}

Apart from specifying the physicsProperties and fluidProperties dictionaries, the case is equivalent to a standard pimpleFOAM case, e.g. in terms of transportProperties, RASProperties, dynamicMeshDict, U, p, fvSchemes, etc.

Code

fluidModel

For the cylinderInChannel test case, we have selected a "fluid" analysis in the physicsProperties dictionary: this means a fluidModel class will be selected; then, we specify the actual solidModel class to be the pimpleFluid class.

The code for the pimpleFluid class is located at:

solids4foam/src/solids4FoamModels/fluidModels/pimpleFluid/pimpleFluid.C

and this code directly ports the pimpleFoam solver code; in particular, see the evolve() function with pimpleFluid.C.