The Gradient filter produces ugly results

[svetlanatkachenko (svetlana)]

Vorticity shows the following:

Y-velocity is much better:

Context: Flow near two parallel inlined heated plates

Same data zoomed out, Vorticity:

Y-Velocity:

Is there something that I can do to make the result look smoother and make sense?

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Q-Criterion using the Gradient filter

Dear all, I am trying to visualize the Q-Criterion as one would normally do with the GradientOfUnstructuredGrid filter. Unfortunately it appears to be integrated in the Gradient filter in 5.10 and I can’t find the old options to calculate the Q-Criterion anymore… Is there a way to do it?

I’m using ParaView 5.11.2 on Windows 11.

Thanks in advance for your advice.

[nicolas.vuaille (Nicolas Vuaille (Kitware))]

Hi,

please share some data to reproduce.

Also you may want to try the 5.12 version or even the 5.13 release candidate (https://www.paraview.org/download/)

[svetlanatkachenko (svetlana)]

Hi @nicolas.vuaille

Thank you for your note.

Attached example data.

a1.vtm (493 Bytes)

Vorticity:

Velocity:

I will check the other paraview versions soon.

How does vorticity work in your version? Could you please check?

[svetlanatkachenko (svetlana)]

What does this mean? This pops up when calculating vorticity in the file attached above, in paraview 5.13 RC.

[nicolas.vuaille (Nicolas Vuaille (Kitware))]

Hi @svetlanatkachenko ,

The vtm is a multi-file file format, you send only the root, so actual data is missing (a1/a1_2_0.vtu).

Concerning the error, it means that your data is a composite data, and some subpart does not have the requested array. Looks at the Information panel (and try the Extract Block filter).

Also please prefer copy-paste error message directly over screenshot: it is easier to read and helps other people find this post in the future

[Kenneth_Moreland]

@nicolas.vuaille

Also please prefer copy-paste error message directly over screenshot: it is easier to read and helps other people find this post in the future

BTW, the Output Messages box has a Copy to Clipboard button to make this copy-paste easier. It’s easy to miss that.

[svetlanatkachenko (svetlana)]

a1_2_0.vtu (66.7 KB)

[Kenichiro-Yoshimi (Kyoshimi)]

The poor aspect ratio of the triangular elements in the cross-section may be causing inaccuracies in the numerical differentiation. Indeed, interpolating the velocity vector on a Cartesian grid using the Resample To Image filter and then calculating the vorticity with the Gradient filter improves the contours.

If the accuracy of the numerical differentiation for the polyhedral cells is not significantly compromised, calculating the vorticity for the polyhedral cells before cutting may improve the contour.