# Visualising structures using Q-criterion in Paraview

I have loaded a state file (.pvsm) of a turbulent channel flow solved using DNS and I want to visualise vortical structures using the Q-criterion but it’s not working out.
I’m not sure what I’m missing because the tutorials seem straightforward.

The velocity components are all stored as points in 3 different arrays (u,v,w) but I can’t seem to be able to calculate the velocity magnitude with the Calculator filter. I use the equation Umag= sqrt(u^2+v^2+w^2) to find the velocity magnitude.

Thanks!

flow_field.zip (58.3 KB)

I don’t know if you can or would like to open zip files.

the u, v and w velocity data are stored within .xmf files separate from the .pvsm file so I had to compress and zip them all together

thanls.

Please share the .h5 files too.

Best,

grid3dc.h5sp (5.3 KB)

grid3du.h5sp (5.3 KB)

grid3dv.h5sp (5.3 KB)

grid3dw.h5sp (5.3 KB)
these are .h5sp files, I hope they are the same?
Many thanks

the files should be named `u.res.hdf5` or similar

The files are quite heavy and for some reason I cannot upload them in this chatbox.

Is there any other way to send them to you or can something else be done?

Many thanks!

Works fine here:

Yes I can visualise the results but I seem to be having trouble calculating the Q-criterion

if you were able to, could you provide a brief walkthrough of how you did it?

thanks

How do you compute it ?

Well, assuming the research I have made is correct, the first step is to create an array (Umag) with the three velocity components (u,v,w) using the calculator filter.

I have been struggling to do this, then you use the Gradient of Unstructured Dataset 1 filter to calculate vorticity and Q criterion.

So, while my main goal is to calculate the Q criterion I haven’t been lucky to find the Umag. I get a blank box when I apply the calculator filter as shown in the image below:

It is actually pretty simple.

I get a blank box when I apply the calculator filter as shown in the image below:

This is an outline, switch representation to surface to see the surface instead of the outline

the first step is to create an array (Umag) with the three velocity components (u,v,w) using the calculator filter.

The first step is to create a Vector with the three velocity components (u,v,w) using the calculator filter or the dedicated filter, MergeVectorComponents

Here is a state file: 3d_visualisation_kw.pvsm (971.6 KB)

Here are the manual steps: -

• run ParaView
• open u.res.xmf, Apply
• open v.res.xmf, Apply
• open w.res.xmf, Apply
• select all three readers in the pipeline browser by keeping Ctrl pressed,
• Filters → AppendAttributes, Apply
====== (new steps below)
• Filters → MergeVectorComponents, select u,v,w, Apply
• Filters → Gradient, Select “Vector”, show advanced options (cogwheel), check QCriterion, Apply
• Switch representation to surface, show QCriterion

1 Like

Thanks, I’ve been able to visualise the velocity magnitude

However, I don’t seem to have the Mergevectorcomponents filter. Perhaps it’s in a later release of Paraview?
I’m currently using v5.4.1