FWH permeable surface

[Tohid2020]

First of all thank you for creating Acoustic library, I have some questions. In order to create FWH surface for both 2D & 3D cases, What Should I do? Should I create STL file in ASCII format and then put it inside constant folder and create trisurface folder and paste inside it and the use:

is this correct? what about 2d cases? I mean what should I do with the domain depth?

Farassat1A-triSurface { type FfowcsWilliamsHawkings; formulationType Farassat1AFormulation; #include "commonSettings"; patches (); interpolationScheme cellPointFace;

    surfaces
    (
            *******
            {
                 type               sampledTriSurfaceMesh;
                 surface            *****.stl; 
                 source             cells;
                 interpolate        false;
            }

);

Thank you again in advance for your replying. I greatly appreciate your time and I look forward to hearing from you soon.

[mkraposhin]

Hi, for a 2D case you can select any depth of a domain. But you must set corresponding normalizing length (dref) in the dictionary. You can see old versions of library as an example, e.g. https://github.com/unicfdlab/libAcoustics/tree/digitef-dev-1912/Tutorials/monopole2D .

But, please be careful with the 2D version of the library. Later we've found that while this simplification may be good for learning / testing purposes, it might be also incorrect from the physical point of view.

[Tohid2020]

Thank you for replying. As I insert 2D mesh to openfoam, it adds some thickness for 2D mesh like 0.05 . Here when I want to use another fwh source surface (I mean not the boundaries like inlets, outlets or walls). then should extrude that fwh surface as 0.05? May I request tutorial for 2D case with external stl surfaces?

Thank you for your great works

[mkraposhin]

You can try both variants: when an STL surface has precisely the same depth, as an computational domain or when an STL surface intersects boundaris of a 2D domain.

[mkraposhin]

It looks like, I don't have a 2D case with STL surface. So, you should build it yourself and post here your questions.

[Tohid2020]

@mkraposhin Thank you for replying. May I have some questions? How is it possible to detect jet screech noise with lib-acoustics? I mean does screech tone appear always? or in some cases it may not be appeared? I know this question may not directly related to the lib-acoustics but would you mind answering it? I am using waveTransmissive BC at outlet and I change the lInf and it always is reflective. How can I avoid outlet reflection? Would you please answering this quesion? outlet { type waveTransmissive; field p; psi thermo:psi; gamma 1.4; fieldInf 101300; lInf 0.3; value uniform 101300; }

Thank you and Best Regards