Exporting tensor data

I need some help with exporting field data to a text file.

Context:
I’m doing some OpenFOAM and postprocessing in ParaView (of course ;-)). I need to send some of my data in order to collaborate with a colleague who has his own code.

ParaView Versions
4.1.0 & 5.1.2

Workflow

  1. I import my simulation no problem.
  2. Calculate derivatives of velocity, also smooth sailing with the built-in filters.
  3. However, when it comes time to export the data, I’m getting strange results.

Problem
When I try to save the data (Ctrl+S method), I get a file, but I don’t understand the format. Previously when I had to export just the velocity (i.e. a vector), I have a csv file with "U:0","U:1","U:2","Points:0","Points:1","Points:2". This was very easy to understand.

Now I seem to get:
"U:0","U:1","U:2","VectorGradient:0","VectorGradient:1","VectorGradient:2","VectorGradient:3","VectorGradient:4","VectorGradient:5","VectorGradient:6","VectorGradient:7","VectorGradient:8","Cell Type"

I don’t seem to get what is this entry “Cell Type”.

Is it at all possible to get columns of "VectorGradient:0...VectorGradient:8","Points:0","Points:1","Points:2"

I’ve also tried cutting a slice and exporting that, but also no luck. I’ve tried the three available “Field Association” options.

Could someone please point me in the right direction?

Hello and welcome.
Please share your data to reproduce your issue.

Many thanks for the warm welcome.

I’ve cooked up a smaller case to make it easier to upload. Please find it attached. There is a ParaView state file. pitzDaily_MWE.tar.gz (1.4 MB)

Could the issue I’m facing be related to the representation on points vs cells?

  • From what I understand, OpenFOAM exports data in cell centers.

  • ParaView automatically (by default) interpolates it to point data.

  • The “compute derivatives” filter only works for point data (can’t understand why),
    ** but outputs in cell centers.

  • The best solution that I found so far was to use the “Cell Center” filter. It seems to map the derivatives computed at cell centers into point data.

From what I could see, there is no filter/option to show cell center locations (but I hope to be wrong).

Is there a way to compute the derivatives from the cell centers?

Thanks in advance.

ParaView automatically (by default) interpolates it to point data.

You can color by cell data.

The “compute derivatives” filter only works for point data (can’t understand why),
** but outputs in cell centers.

CellDerivatives is a filter that computes derivatives of scalars and vectors at the center of cells. You can choose to generate different output including the scalar gradient (a vector), computed tensor vorticity (a vector), gradient of input vectors (a tensor), and strain matrix of the input vectors (a tensor); or you may choose to pass data through to the output.

Is there a way to compute the derivatives from the cell centers?

Unless I’m mistaken this is what the compute derivative filter do.