# Pipe flow using rhoSimpleFoam mot converging

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July 9, 2015, 11:04
Pipe flow using rhoSimpleFoam mot converging
#1
New Member

Aude
Join Date: May 2015
Posts: 5
Rep Power: 3
Hello Foamers!!

I'm a newbie to OpenFOAM and i'm struggling a bit with a case I have to run for my PhD.

The idea is the following:
We are dealing with half a pipe (Diameter: 0.05m - Lenght: 0.4m) and we want to simulate the flow passing inside it and compare it with experimental data.

We are using air (which we consider to be following the perfect gas law), the exit Mach number should be 0.65 (so we go for a compressible solver --> rhoSimpleFoam), and the static pressure at the outlet should be the ambient pressure (98916Pa).
The walls of the pipe are considered adiabatic.

I measure a total pressure at the inlet as well as a total temperature.

Therefore: I am setting up the following files for my case:

0/p
----------------------------------------------
dimensions [1 -1 -2 0 0 0 0];

internalField uniform 98916;

boundaryField
{
inlet
{
type totalPressure;
p0 uniform 131392;
gamma 1.4;
}
lateralwall
{
}
symmetrywall
{
type symmetryPlane;
}
outlet
{
type fixedValue;
value uniform 98916;
}

0/U
----------------------------------------------
dimensions [0 1 -1 0 0 0 0];

internalField uniform (0 0 -217);

boundaryField
{
inlet
{
type fixedValue;
value uniform (0 0 -217);
}
lateralwall
{
type fixedValue;
value uniform (0 0 0);
}
symmetrywall
{
type symmetryPlane;
}
outlet
{
}
}

0/T
----------------------------------------------
dimensions [0 0 0 1 0 0 0];

internalField uniform 277;

boundaryField
{
inlet
{
type totalTemperature;
T0 uniform 300;
gamma 1.4;
}
lateralwall
{
}
symmetrywall
{
type symmetryPlane;
}
outlet
{
}
}

I'm using a k-omega SST turbulence model, and running with rhosimpleFoam solver.
I don't get any error messages, but I cannot manage to make this computation converge.
My pressure distribution after some iterations increases and makes no sense (values close to 1.3e5 Pa) and neither does the velocity.
Is something wrong with my boundary conditions? Am I over-constraining or under-constrainig the problem?

Any help would be much appreciated.
Attached Images
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 July 10, 2015, 04:47 #2 Senior Member   Joachim Herb Join Date: Sep 2010 Posts: 391 Rep Power: 11 Have you tried zeroGradient for the pressure inlet boundary condition? It is used in the tutorial for rhoSimpleFoam

 July 10, 2015, 07:57 #3 New Member   Aude Join Date: May 2015 Posts: 5 Rep Power: 3 Yes I also tried imposing a zeroGradient at the pressure inlet BC. The pressure field was still not making any sense. But if I put a zeroGradient at my inlet for the pressure, I cannot impose a total pressure there. And this is one of the measurements I'd like to compare

 July 10, 2015, 12:03 #4 New Member   kh Join Date: Jun 2015 Posts: 9 Rep Power: 3 Hi, Maybe the velocity is reversed. Now is negative in Z direction and your pressure BC has outlet on top? K

 July 10, 2015, 19:05 #5 Senior Member   Joachim Herb Join Date: Sep 2010 Posts: 391 Rep Power: 11 I think you cannot specify the (total) pressure and the velocity at the inlet. If you give the pressure at the outlet and the velocity at the inlet you get (total) pressure at the inlet from the simulation.

 Tags compressible flow, openfoam 2.1.x, pipe flow

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