CFD Online Discussion Forums - Is there a good absorbing BC somewhere?

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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?

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;

    }