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STAR-CCM+ FWH Permeable Surface (CAA)

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Old   December 4, 2020, 01:59
Default STAR-CCM+ FWH Permeable Surface (CAA)
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Dear all,

I have simulated LES for supersonic jet flow. The computational domain is cylindrical and it includes the nozzle geometry. Currently, there is only 1 Region.

I need to compute the jet noise in the far-field and therefore need to include a permeable FWH surface that encapsulates the noise sources in the exhaust (e.g. a conical shape that surrounds the jet flow), so that the FWH analogy can be used to propagate the noise sources into the far-field.

Does anyone know how to construct a permeable FWH surface? Should I draw the FWH surface using the native 3D-CAD modeler or using New Shape Part (under Parts). Should the FWH surface be a separate region from my computational domain? (The FWH surface must be an "internal interface").

I have seen some tutorials (such as https://support.sw.siemens.com/en-US...ience=external) but they do not instruct on how to create a permeable FWH surface.

You can have a look at the images attached (of my computational domain and instantaneous flow field).

Your help is greatly appreciated!

mnws
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File Type: jpg domain.jpg (139.0 KB, 5 views)
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Old   December 24, 2020, 02:43
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You need to split the computational domain into two pars. One part contains the noise sources and the rest domain is the other part. The interface between two parts is the permeable surface.
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Old   December 27, 2020, 23:26
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Dear Rinia,

Thank you for your reply. I'm currently trying that.
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Old   December 30, 2020, 02:59
Default FWH surface
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Dear Rinia,

I constructed 2 regions, by subtracting a cone from a cylinder.

The interface between the 2 regions, (which is the outer surface of the cone) is the FWH surface. This surface is meant to encapsulate all the noise sources from the turbulent eddies.

As can be seen in the image attached (2 regions.jpg), the conical surface generated is not perfectly conical after meshing.

I noticed that the native STAR-CCM+ mesher is able to preserve surface perimeters well for outer boundaries (as can be seen for the cylindrical outer boundary), but the inner conical surface resulting from the subtracted cone does not appear to have a good resolution.

It appears slightly rough or crumpled. The cross section appears polygonal rather than circular. (FWH surface.jpg).

Do you know how I can ensure that the conical shape is preserved?

I have tried adjusting the parameters and tolerances for imprinting/subtracting etc. when preparing the regions but cannot improve the quality of the surface.
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File Type: jpg FWH surface.jpg (45.9 KB, 4 views)
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Old   January 3, 2021, 23:52
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Quote:
Originally Posted by mnws View Post
Dear Rinia,

I constructed 2 regions, by subtracting a cone from a cylinder.

The interface between the 2 regions, (which is the outer surface of the cone) is the FWH surface. This surface is meant to encapsulate all the noise sources from the turbulent eddies.

As can be seen in the image attached (2 regions.jpg), the conical surface generated is not perfectly conical after meshing.

I noticed that the native STAR-CCM+ mesher is able to preserve surface perimeters well for outer boundaries (as can be seen for the cylindrical outer boundary), but the inner conical surface resulting from the subtracted cone does not appear to have a good resolution.

It appears slightly rough or crumpled. The cross section appears polygonal rather than circular. (FWH surface.jpg).

Do you know how I can ensure that the conical shape is preserved?

I have tried adjusting the parameters and tolerances for imprinting/subtracting etc. when preparing the regions but cannot improve the quality of the surface.
There is a tesselation density choice when you creat the cone in star ccm. Maybe you can try the 'very fine' level. Moreover, you should refine the cell size on the cone surface.
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Old   January 4, 2021, 22:38
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Thank you for the suggestion! Will give that a try.
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aeroacoustics, ffowcs-williams hawkings, star-ccm+

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