[The]

Hello,

I have a wind tunnel as shown in the picture with a small cylindrical object in the middle, lets call it a needle. I want to mesh the domain, however the needle is so small that I need a very fine mesh to resolve it. However I don't want my tunnel to be meshed this fine. Since they are physically connected on one end what would be the best way to get a fine prism layer mesh around the needle while having a coarser mesh on the tunnel walls with a smooth transition?

I indicated the tunnel prism layers in red. The needle in blue and the needle prism layers in orange.

Thanks a lot in advance!

[fluid23]

parts based meshing with appropriate custom mesh controls.

all due respect, but perhaps you should start with a few of the tutorials to get the basics down.

[The]

Originally Posted by fluid23

parts based meshing with appropriate custom mesh controls.

all due respect, but perhaps you should start with a few of the tutorials to get the basics down.

Currently I have a surface control which allows to implement a finer mesh. However connecting it with the coarser mesh is not as I want it to be, the mesh gets distorted. I hoped for a quick trick but guess I gotta keep going with trial and error

[fluid23]

Sorry, misread that just a bit. Also didn’t realize you had already meshed.

Can you share an image of the poor transition so people can understand what is happening. There is likely a way to fix this through parts based mesh and/or changes to the prism layer mesher settings.

[The]

Hello, sorry for the delayed answere.

I put two Images up so you can better understand my problem: The first image shows the mesh in the area of the small needle with the problematic area. There is a distortion between two prism layers (Wall and Needle) because they will not connect.
The second image shows quite the same but I have drawn in some lines in red and green (red=Prism Layer Mesh of Needle, Green=Prism Layer Mesh of Tunnel Wall) to indicate what I think would be a better solution. Actually I'm not quite sure if that would be the best solution so if there better advises I'm happy to learn more.

Thanks in advance for the help and best regards

Edit: I should notice that I am currently using a surface control on the needle in order to have a smaller prism layer in this area. I don't need that small layers on the wall. Thats why I made two different kind of layers. (Actually in the pictures I have tried to keep the total thickness constant, but it did not solve the problem).

[fluid23]

I played around with this a bit and was able to duplicate this issue. I don't think your red/green sketch is practical. That would probably start to require a structured mesh that star-ccm cannot do.

However, you can take a few steps to improve this considerably. Go in to the prism mesher settings and play around with minimum thickness percentage, layer reduction percentage and near core layer aspect ratio settings. One thing I noticed was that the trimmed cells seemed to not to like to play nice. If you aren't married to this mesh choice, change to polyhedral and you will have a much easier time.

Good luck.

[Aeronautics El. K.]

Originally Posted by The

Hello, sorry for the delayed answere.

I put two Images up so you can better understand my problem: The first image shows the mesh in the area of the small needle with the problematic area. There is a distortion between two prism layers (Wall and Needle) because they will not connect.
The second image shows quite the same but I have drawn in some lines in red and green (red=Prism Layer Mesh of Needle, Green=Prism Layer Mesh of Tunnel Wall) to indicate what I think would be a better solution. Actually I'm not quite sure if that would be the best solution so if there better advises I'm happy to learn more.

Thanks in advance for the help and best regards

Edit: I should notice that I am currently using a surface control on the needle in order to have a smaller prism layer in this area. I don't need that small layers on the wall. Thats why I made two different kind of layers. (Actually in the pictures I have tried to keep the total thickness constant, but it did not solve the problem).

It seems to me that the surface control you have used, stops short of the tunnel's wall, leaving part of the needle outside of the surface refinement. Which probably means that this is a separate surface. So, try to add that surface in the same surface control as the rest of the needle.
Alternatively, you could use a volume control, covering the needle all the way to the wall (and through the wall, it doesn't hurt).