[L2e2o4]

Hello, Ansys community,

Hope you all are having a great day with solutions converging

I want to share the problems that I've encountered recently regarding the re-mesh logic of FENSAP-ICE, specifically, fluent meshing.
I was unsure which sub-thread(s) this post belongs to, as there are no specific threads for FENSAP-ICE.

I have been working on the 2.5D, i.e., only one cell thick at z-direction, airfoil icing simulation under various atmospheric conditions, and the re-mesh feature has been working well.

https://imgur.com/a/mmultishot-loop-D6lqytr

https://imgur.com/a/airfoil-remesh-multishot-7AZyFbF

In short, the airflow is solved by the FENSAP solver at the first step.
Then, the droplet solution or the water collection will be solved by DROP3D solver, and the ice growth by ICE3D.
The re-mesh step is called after ice accretion is done.
The problem is that when I tried to do multi-shot runs for an airfoil in a tunnel, i.e., introducing top and bottom walls to the existing case(s), the re-mesh process won't continue,
and the error message " DID NOT FIND OPPOSITE FACET! (base cell type 3) " appeared.

https://imgur.com/a/didnotfindfaceterror-I8wWyjY

The key difference between the two cases is that there are 3 wall boundaries for the (tunnel + airfoil) case, whereas there is simply 1 for the airfoil-only case.
BC_2000 represents the airfoil in either case, BC_2001 and BC_2002 are the top/bottom tunnel walls.

https://imgur.com/a/ice3d-bondaries-...l-only-tsmOaiZ

https://imgur.com/a/ice3d-boundaries...tunnel-au5QQyM

According to the user manual of FENSAP-ICE 2022 R2, the re-meshing process consists of several steps:

================================================
The Fluent Meshing scripts will carry out the following operations:
• Convert the script inputs ($grid_input, $grid_next…) to simple variables to be used throughout the script.
• Extract the previous and next shot numbers (ex: 000002, 000003) from these variables.
• Clean up and remove any files that exist from previous simulations.
• Create a shell.cas file containing all boundaries from the initial mesh that will be used during the remeshing operation.
• Copy the most recent iced geometry STL file to a general ice.stl name for use during the remeshing operation.
• Call Fluent Meshing with the remeshing.jou journal file to perform the remeshing operation, creating a new mesh (newmesh.msh and newmesh.cas).
• Convert the newmesh.cas file to FENSAP format, using the -zonebc option to preserve the boundary names.
• Interpolate the FENSAP and DROP3D and roughness solutions onto the new grid.

The example remeshing.jou journal file performs the following steps within Fluent Meshing:

• Read the original grid converted to Fluent format, called shell.cas, as a boundary mesh omitting volume cells.
• Remove the wall boundary zones – they will be replaced by zones coming from the ice.stl file.
• Triangulate quad elements on any boundary zones, like symmetry planes.
• Import the ice.stl file from the current shot.
• Specify curvature and proximity based sizing functions.
• Extract boundary zone outer edges - (do not extract features based on angles as this might also extract unwanted ice surface sharp edges).
• Create a material point to initiate surface wrapping projections.
• Wrap the entire domain using the computed sizing function
– This is the surface remeshing step.
– Wrapping feature is well automated and smooths the surface while wrapping over features smaller than the local sizing function.
– Local sizing function controls the level of smoothing and defeaturing that will take place during wrapping.
– The outcome of wrapping is always a high quality, low skewness surface mesh.
• Specify prism layer settings.
• Auto mesh the volume, creating prism layers and filling the rest with tetras.
• Write the new mesh file and exit.

FENSAP-ICE uses one-element-thick grids extruded in the Z direction to solve the air, particle, and film equations in 2D in X and Y coordinates.
In the remeshing process these grids will be converted to very fine 3D grids unless remesh-2d? flag is set to true (#t).
The 2.5D process remeshes one of the symmetry planes and extrudes it in the Z direction to form the one-element-thick grid before writing it out.
The following figure shows the difference between 3D and 2.5D remeshing of the same iced airfoil:

There are some requirements for the 2.5D remeshing steps to work properly:
• Span should be in Z direction.
• Z-symmetry BC (4300) should be set on both symmetry planes.
• One of the 4300 boundaries should be placed at Z = 0 exactly.
• The material point should be placed very close to the trailing edge of the geometry, at mid-span.

The wrapping process will initially collapse the symmetry planes to a bubble enveloping the walls,
to save time in the meshing process. The material point should be captured within this bubble.
The original symmetry planes will be restored by intersecting the wrapped geometry afterwards.

================================================

According to this document and the boundary condition settings, plus Figure 5 showing the wrapping process, my humble guess is as follows:
During the re-mesh process, which happens between the "ICE3D" and "displaced grid steps", the tunnel walls were disregarded, as they are not part of the (airfoil + ice) geometry.
The reason is that there is only one material point you can set, and it defines the region that would be recognized as the airfoil + ice, which it is designed to solve, I believe.

https://imgur.com/a/manual-wrapping-...-point-le41qwB

My question is, is the topology (tunnel walls + airfoil) not compatible with this specific re-meshing process?

https://imgur.com/a/mp-setting-CC6aidO

P.S. The re-mesh using the ALE method actually worked However, I need a re-mesh model sophisticated enough to simulate more complex icing.

Thank you for your time and I appreciate your input!


Best,
L2e2o4

[L2e2o4]

Sorry this is my first post here and somehow the images using external links are not showing: (

The fig for multi-shot loop:
https://imgur.com/a/mmultishot-loop-D6lqytr


The airfoil remesh process:
https://imgur.com/a/airfoil-remesh-multishot-7AZyFbF


The error message from the tunnel + airfoil topology:
https://imgur.com/a/didnotfindfaceterror-I8wWyjY




The boundary settings for airfoil-only & airfoil + tunnel walls:
https://imgur.com/a/ice3d-bondaries-...l-only-tsmOaiZ

https://imgur.com/a/ice3d-boundaries...tunnel-au5QQyM


The wrapping process and material point:

https://imgur.com/a/manual-wrapping-...-point-le41qwB

The material point setting in ICE3D:

https://imgur.com/a/mp-setting-CC6aidO

[PierceH]

Hello,


I'm having problems running the Fluent Remeshing in general, do you think you could provide help. I keep experiencing an STD error after the icing process.

[L2e2o4]

Originally Posted by PierceH

Hello,


I'm having problems running the Fluent Remeshing in general, do you think you could provide help. I keep experiencing an STD error after the icing process.

It sounds like your issue is different from the original topic here, so it would be best to post it as a separate thread. Including your geometry, setup details, and the full error message will help others understand and respond more effectively.

The forum’s Guide: How to ask a question actually encourages posting your own thread for new issues, so feel free to do so.

If your question is specifically about Fluent remeshing using FENSAP-ICE, I’d be happy to help once it's posted in the right place.