Scattering by a half-plane

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Hello,

I am simulating the scattering of acoustic waves by a half-plane. The domain consists of a rectangular box with the half-plane at the bottom. The box is surrounded by PMLs shown in purple in the image below. Periodic boundary conditions are used in the front and back faces and the background field is a plane wave in the x-direction. I am using the pressure acoustics, frequency domain module and I would like to add a background mean flow in the x-direction.

I have thought of two possibilities:

1) Use the linearized Euler Equations first just to add the mean flow, and then use the acoustics module, but I didn't manage to couple the two things.

2) Modify the wave equation to go from the Helmholtz equation: to a convected Helmholtz equation

I tried using the dipole source as this will give the first order partial derivative, but the results I got don't seem to agree with the analytical model I have.

Is there any better way to include the effect of the background flow?

Thanks



2 Replies Last Post Jul 22, 2025, 3:33 p.m. EDT
Mark Cops COMSOL Employee

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Posted: 2 days ago Jul 21, 2025, 10:02 a.m. EDT
Updated: 2 days ago Jul 21, 2025, 10:04 a.m. EDT

Hi Jorge,

If you can assume an irrotational and inviscid background flow, then use the Linearized Potential Flow, Frequency Domain interface. You can specify the mean flow simply by a user-defined expression, or solve a CFD problem for the mean flow using the Compressible Potential Flow interface. You can find this example of the former: https://www.comsol.com/model/doppler-shift-1376

-Mark

Hi Jorge, If you can assume an irrotational and inviscid background flow, then use the Linearized Potential Flow, Frequency Domain interface. You can specify the mean flow simply by a user-defined expression, or solve a CFD problem for the mean flow using the Compressible Potential Flow interface. You can find this example of the former: https://www.comsol.com/model/doppler-shift-1376 -Mark

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Posted: 22 hours ago Jul 22, 2025, 3:33 p.m. EDT

Hi Mark,

Thanks a lot for your reply!

I understand your point of view, however for validation of my simulation I must radiate the pressure on the plate to the far-field and compute the directivity patterns at different non-dimensional frequencies. I am trying to use the acoustic pressure, frequency domain since the far-field computation is straightforward using the far-field module (K-H integral). For the flow I can assume only inviscid and irrotational flow, so I guess it should be either linearized compressible or linearized Euler.

Do you think it would be possible to include the mean flow effect by adding a source term or other modification in the acoustic pressure, freq domain module?

Thanks

Jorge

Hi Mark, Thanks a lot for your reply! I understand your point of view, however for validation of my simulation I must radiate the pressure on the plate to the far-field and compute the directivity patterns at different non-dimensional frequencies. I am trying to use the acoustic pressure, frequency domain since the far-field computation is straightforward using the far-field module (K-H integral). For the flow I can assume only inviscid and irrotational flow, so I guess it should be either linearized compressible or linearized Euler. Do you think it would be possible to include the mean flow effect by adding a source term or other modification in the acoustic pressure, freq domain module? Thanks Jorge

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