FreeCAD Forum

oliveroxtoby wrote: ↑Thu May 26, 2022 7:57 pm @thschrader's case works for me, as does the attached which has been modified to have the same boundary conditions as your original case. This is using cfMesh - I get mesh quality issues when using gmsh, probably due to a small gap or misalignment somewhere (which cfMesh and snappyHexMesh tend to be more robust to by their design).

Crossleyuk wrote: ↑Wed May 25, 2022 7:58 pm Hi TH,

I tried your case and sure it meshed in cfMesh and gmsh but could not get it to run at all. So I've continued with my rebuild using gmsh and note that the case fails every time the Residuals climb higher. Here is what I'm getting every time.

Body_Cyl_Axial_Complete_Rev_P2_Large_Residual.png

Cheers and thanks for the contact again.

Michael

Don't forget to look at the checkMesh output - I suspect you will find it is poor in the gmsh case. Otherwise, uploading the exact case that is giving you an issue should make it possible for someone to assist.

You beat me to it Oliver and thanks yet again to you and ALL. I had just completely rebuilt my model with little success so changed to "Part" rather than Part Design and finally a Fusion. That again failed with elevated Pressure residuals so your's is now running with me fingers crossed, after finishing this post. Will let you know the result and happy to offer more details of my additional tries if you think it may be of assistance

Short question:
I am interested in the flow field of the balcony (the "comfort-zone" ).
Inlet speed is low, only 5 m/s. Simulation gives smooth residuals.

But checkmesh says there are some non-orthogonal elements from gmsh.
In the end checkmesh says “Mesh ok”. Sooo..the mesh is ok? Or not?

The writing of the 120 non-ortho elements: Are they removed?
Thanks.
Thomas

See
https://www.cfdsupport.com/OpenFOAM-Tra ... de131.html

thschrader wrote: ↑Sun May 29, 2022 3:40 pm But checkmesh says there are some non-orthogonal elements from gmsh.
In the end checkmesh says “Mesh ok”. Sooo..the mesh is ok? Or not?

The writing of the 120 non-ortho elements: Are they removed?

The checkMesh run is informational only. Nothing is removed.

The mesh is fine. That level of non-orthogonality is generally OK (it does depend on the solver to an extent - one can't give a specific number that is ok; ultimately the proof is in whether the solution is stable or not). The number of '*'s next to the message indicates its severity, from 1 to 3. So this is more a notification that an error. In time CfdOF should parse the output accordingly so that it's easier to follow.

Hello Again and very sorry for this long question!

I'm back for more support after the graet help you provided in May this year. Many thanks for that, you made it very clear that I should uses the Part Workbench and Fusion. My imediate reaction was "great, that's a lot better and solves the problem". As a result, I decided to start the next stage of my CFD research exercise and commenced key changes to my device that I am now calling a Vortex Restrictor (VXR) rather than Vortex Amplifier (VXA).

It went well and I now have the following 3D design and internal Flow regime boundaries.

The problem is that, unlike all my previous Part Design Workbench models, I it will not result in clear vortex generation by the tangential flow flows.

Michael

I'm sure, but still trying to confirm, that the reason is that the flow from the four axial "control" ports is not entering the vortex chamber. In the past, selecting a two adjacent boundary faces within the model reslted in a clear boundary between the two boundaries. But this no longer is the case as indicated below.


My thoughts are suggesting that flow is not passing from the open end of the control port into the vortex chamber. I could not make it clear that the Vortex Chamber and Control Port bodies were independant and the result seamed to be a boundary between the two preventing flow. I intoduced a disc between the two and made it an Open Boundary on both sides.

Here is my most recent model version (P11), but I am still learning and guessing big time.

Many many thanks in anticipation and realy sorry about the complications here, but any asistance would once gain but massively greatfully received.

When re-running an airfoil simulation, I realized that the generated stl
is too rough. The edges 1+2 are in fact straight lines, wich gives a weird result.
When reimporting the stl, you can see that the triangulation is to bad.
How can i get a finer stl mesh?
File for testing:

thschrader wrote: ↑Thu Jul 07, 2022 3:16 pm When re-running an airfoil simulation, I realized that the generated stl
is too rough. The edges 1+2 are in fact straight lines, wich gives a weird result.
When reimporting the stl, you can see that the triangulation is to bad.
How can i get a finer stl mesh?
File for testing:
naca4415ts.FCStd
stl_too_rough.JPG

You can reduce the STLRelativeLinearDeflection in the properties of the mesh object. You have to reduce it to 0.001 in this case to see any improvement. Not sure what's happening there - I'll have to look into it.

oliveroxtoby wrote: ↑Thu Jul 07, 2022 8:46 pm .... I'll have to look into it.

Same happens with the model from Crossleyuk.

@Crossleyuk:
The boundary condition "Diffusor_Enty_open" has no face assigned.
In my opinion there is a "bug" in your model. When reloading the generated
stl after case writing and checking the stl, I get some errors (the yellow points).
Second check is "Mesh is NOT a solid". Which is not a good sign...
The generated mesh is to "rough" (because of the stl), especially at the funnels.
Maybe this is the reason why your results differ from previous runs.

Thank you TH, I'll look into your reply tomorrow

Thank you TH.

"Diffusor_Enty_open" is in fact no longer used. I remodlled the chamber face that the diffuser connects to and added a hole for air to exit and enter the diffuser. I just didn't remove the now blank boundary. The axial glyph chart is showing that the move was correct. I would now have to add a disc in that area in order to now add an open boundary. So no need for it now.

This also alloweded me to remove the chamber exit face from the tangential flow port regions at the periphery that I wanted to be able to also add an independant boundary to. But this new boundary still closes the axial flow region so that is why I added the "Control Entry" discs and made them open faced.

I need to read your "checking stl" I don't know how to do that yet.

Many many thanks once more for your interest and support

Michael

Crossleyuk wrote: ↑Sat Jul 09, 2022 9:18 am ...
I need to read your "checking stl" I don't know how to do that yet.
...

My idea was to improve the stl by using the Mesh-design wb (Meshes/Create mesh from shape),
using netgen or gmsh, and overwriting the stl in the meshcase folder.
But that wont work, you have to change the stl-patch files too, which is tedious work, if even possible...

Checking written stl in meshcase-folder: