CFD Online Discussion Forums - [swak4Foam] Inlet velocity profile for turbulent pipe flow using swak4Foam

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Inlet velocity profile for turbulent pipe flow using swak4Foam

Hi, I wanted a fully developed inlet velocity profile for my 3D-case and I decided to implement it using swak4Foam since I couldn't figure out how to do it with native OpenFOAM tools. So, I thought I'd share my solution here since it took me a while to figure it out.

Please note that in my case the inlet pipe centerline run along the y-axis, but it should by easy enough to modify for other cases too. Turbulent velocity profile is calculated using the power law formulation.

Code:

        pipe_inlet

        {

              type groovyBC;

              value uniform (0 0 0);

              variables (

                "n=7;"  //power law coefficient n

                "d=0.125;"  //pipe diameter

                "volFlowRate=0.1;"  //volumetric flow rate

                "Umean=volFlowRate/(pi*pow((d/2),2));"   //calculate mean velocity

                "Umax=Umean*(((n+1)*(2*n+1))/(2*pow(n,2)));"  //calculate max velocity

                "profile=Umax*pow(1-sqrt(pow(pos().x,2)+pow(pos().z,2))/(d/2),(1/n));"

                //calcucate power law velocity profile Umax*(1-r/R)^(1/n)

                );

              valueExpression "normal()*-profile";

              //apply to boundary, normal() is surface normal vector and minus is needed for inflow

        }

I hope someone finds this useful :)

PS: swak4Foam development version compiles for OpenFOAM-2.3.x and at least groovyBC is working fine

Hi Zor,

Do we have to make any other change in any other folder or the code which you have given is good enough to implement the fully-developed boundary condition?

Thanks,

Rohit:)

You need to install swak4Foam according to instructions.

Files that need to be mofidied are 0/U and system/controlDict (add swak4Foam libs, which is shown in the installation instructions).

Hi,

hope someone helps me as this thread is quite old...

Anyway, I set the inlet profile for my pipe simulation according to the upper BC for inlet.

When I set the power law coefficient as 1/n<1, simpleFoam crashes (floating point exception).
For values 1/n>= 1, simpleFoam works fine, but my inlet profile isn't real.

this is my error:

Code:

Time = 1



#0  Foam::error::printStack(Foam::Ostream&) at ??:?

#1  Foam::sigFpe::sigHandler(int) at ??:?

#2   in "/lib/x86_64-linux-gnu/libc.so.6"

#3   in "/lib/x86_64-linux-gnu/libm.so.6"

#4  pow in "/lib/x86_64-linux-gnu/libm.so.6"

#5  Foam::pow(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) at ??:?

#6  Foam::pow(Foam::UList<double> const&, Foam::UList<double> const&) at ??:?

#7  parserPatch::PatchValueExpressionParser::parse() at ??:?

#8  Foam::PatchValueExpressionDriver::parseInternal(int) at ??:?

#9  Foam::CommonValueExpressionDriver::parse(Foam::exprString const&, Foam::word const&) at ??:?

#10  Foam::CommonValueExpressionDriver::evaluateVariable(Foam::word const&, Foam::exprString const&) at ??:?

#11  Foam::CommonValueExpressionDriver::addVariables(Foam::exprString const&, bool) at ??:?

#12  Foam::CommonValueExpressionDriver::addVariables(Foam::List<Foam::exprString> const&, bool) at ??:?

#13  Foam::CommonValueExpressionDriver::clearVariables() at ??:?

#14  Foam::groovyBCFvPatchField<Foam::Vector<double> >::updateCoeffs() at ??:?

#15  Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh>::GeometricBoundaryField::updateCoeffs() at ??:?

#16  Foam::fvMatrix<Foam::Vector<double> >::fvMatrix(Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&, Foam::dimensionSet const&) at ??:?

#17  

 at ??:?

#18  

 at ??:?

#19  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"

#20  

 at ??:?

Floating point exception (core dumped)

can't really uderstand why I have this error, can someone help me please?

this is my check Mesh -allGeometry -allTopolgy log

Code:

............

 ***Cells with small determinant (< 0.001) found, number of cells: 100

  <<Writing 100 under-determined cells to set underdeterminedCells

    ..............

Failed 1 mesh checks.



End

are those 100 cells giving me the error?

Thank you very much.

Hi student666,

I have just encountered the same error. Have you made any progress on this since your last post?

Regards,
Mitch

Quote:

Originally Posted by Mitchell Baum (Post 586205)

Hi student666,

I have just encountered the same error. Have you made any progress on this since your last post?

Regards,
Mitch

My issue was related to a very small cell size. I solevd it by meshing with dimension of the cells bigger. hope it can helps you. Cheers