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sonicFoam unexpected pressure damping

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Old   November 24, 2016, 07:21
Default sonicFoam unexpected pressure damping
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Max Braun
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Hello everybody,

I am trying to run a simple case with sonicFoam and got some undesired damping. I build a tube, 2 meters long, with an oscillating pressure (p' = 1000*sin(t) Pa) as inlet and a waveTransmissive condition as outlet. I was hoping to see a nice sin wave moving through the domain, but there is some kind of damping, even though there is no viscosity (mu = 0). I attached a picture of some pressure probes located a 0.01m, 0.2m 1m and 1.9m. The violet probe at 0.01m shows my nice sin wave but the other ones, especially at 1m (blue) and 1.9m (yellow) show a different amplitude.

I am using OpenFoam 4.1 and the simulation is run at 293.15 K and 100,000 Pa without flow (U = (0 0 0)). I already tried different meshes (1D and 2D, 40-100 cells per wave length), different lInf's in the waveTransmissive condition (0.1-20), different time steps (around 1e-05), different frequencies (170-340 Hz), different amplitudes (100-1000) and different conditions for U and T (zeroGradient, waveTransmissive).

Nothing worked so far to preserve the amplitude so I was hoping for some advise. Like I said, there is a picture attached with the pressure probe data and you may find my inlet and outlet condition for the pressure below.

Thank you very much in advance.

Sincerely,

Max

---------------------------------------------------------------------------------------------------------------
two of my boundary conditions for p:

inlet
{
type uniformFixedValue; //formerly oscillatingFixedValue
uniformValue sine;
uniformValueCoeffs
{
frequency 170;
amplitude 1000;
scale 1;
level 100000;
}
}

outlet
{
type waveTransmissive;
field p;
psi thermo:psi;
gamma 1.4;
fieldInf 100000;
lInf 3;
value uniform 100000;
}
Attached Images
File Type: jpg 1Dtube.jpg (123.0 KB, 9 views)
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