CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM Running, Solving & CFD (http://www.cfd-online.com/Forums/openfoam-solving/)
-   -   Is there a good absorbing BC somewhere? (http://www.cfd-online.com/Forums/openfoam-solving/105002-there-good-absorbing-bc-somewhere.html)

jam July 20, 2012 08:06

Is there a good absorbing BC somewhere?
 
Hi,
I am looking for a good absorbing BC and cannot find one. I find it quite strange that none exist in general for CFD. I am trying to do some aeroacoustic calculation and I really need to dump the outgoing flux to the surrounding environment. I did try waveTransmissive and zeroGradient but after some runs, the noise on the boundary is accumulating and the system crashes. I found one more BC called convectiveVelocity specifically made for acoustic problem. The reflection is much lower than with waveTransmissive but is still too high and the system crashes after some runs.

I would like to see something like
Code:

        type          absorbing;
        value        everything;

Any hope of getting something close to that?

jam September 10, 2012 13:12

I think that I finally have a good solution to this problem. It has to do with the value assigned to lInf. (Linf)

A first , I was trying with the number from some tutorials which is around 1 most of the time. I then tried with 0 and it give total reflection or something very bad. I then slowly increased form 0 to 1e-5 ,1-4 and so on and I saw some improvement. The final value for almost no reflection at the external boundary is
Code:


  outlet
    {
        type            waveTransmissive;
        gamma          1.3;
        fieldInf        101325;
        lInf            0.001;
        value          uniform 101325;
    }



All times are GMT -4. The time now is 20:04.