Pseudocolor plot on boundary

[DarrelRobertson]

Trying to get a pseudocolor plot on the surface of an object but not quite getting what I need. Any help would be much appreciated. I have a sim of flow over a body with the interior of the body modelled as well. I want a plot of the air properties in the layer on the surface of the body. I.e the values in the first cells immediately outside the body. If I slice the body in half and switch off the body material I can see the surface properties that I want from the inside out. I'd like that view from the outside so I can see the whole outside. If I go to Slicing - Boundary, I get the surface, but it is giving me the values of the cells immediately inside the body (which for my case are not interesting). Not sure exactly how the boundary slice works, but is there any way to tell it which side of the boundary I want the values from? I don't have any mixed cells.

Darrel.

[JustinPrivitera]

Hi @DarrelRobertson. I think Boundary Slice gives you material boundaries, which look to me to be comprised of 2D faces embedded in 3D space. I don't see how there would be a difference of values on one side or another.

So I'm not quite sure I understand your use case. Is there any chance you could share a screenshot or better yet, some of your data so that we could look?

[DarrelRobertson]

The values I want are cell centered not node centered, something like this:

There is a set of 2D faces that make up the boundary between the air and the body. Below is what I get when I try to just view the surface. Apologies for the silly units. Multiply by 1e11 to get W cm-2.

I can share data, but I don't have a toy case made and the data files for this run are 1GB per timestep. I can put one on Box or otherwise let me know what works for you.

[JustinPrivitera]

Hi @DarrelRobertson. I saw that you shared data with me via box; I emailed you since I was unable to access it. Is it possible to attach data to this github discussion as a tarball or zip file?

[JustinPrivitera]

I think the Boundary Operator chooses which side of the material interface to draw based on material id, which is an internal value that may or may not be exposed in your dataset. The material id is an assignment of a unique integer to each material in a material set. I believe the Boundary Operator chooses the value by picking the cell with the lower material id. If you switched the order of your materials, perhaps you would see the values you wish to see.

Another thing we could try is using the External Surface operator: You might try making a pseudocolor plot, performing material selection such that the body is removed, and then using the external surface operator to view it. However, the external surface operator will show you the surface for the entire remaining mesh, so you will need to sphere clip/threshold or otherwise remove the excess geometry.

Does that make sense/does that work with your data? If you can provide me the data I can also try to take a look and figure out a solution.

[JustinPrivitera]

I added #21093 to track the feature request for boundary slice options.

[JustinPrivitera]

Using your toy problem, I did the following:

1. Create a scalar expression called matvf_1 with this definition: matvf(, 1). The matvf expression gets the material volume fraction for a specified material. Material 1 in your toy problem is the RV.
2. Create a scalar expression called recentered_matvf_RV with this definition: recenter(matvf_1). This recenters our volume fraction scalar to be a node centered variable. You could try to plot a pseudocolor plot of it to see what we have made:

4. Next create a pseudocolor plot of density and add the Slicing/Isosurface operator. Open the operator settings and change the operator variable to be recentered_matvf_RV and Select By to Value(s) and the value should be 0.5, or maybe 0.49 or below. The operator attributes window should look like this:

6. Now you should click apply and draw and you should see your answer:

[DarrelRobertson]

Awesome! Many thanks for figuring out how to do this without re-running the sim.

[JustinPrivitera]

You are very welcome!