Plotting OpenFOAM .dat files in ParaView

Hey there,

It’s Robin from CFD Engine & I’m back with a super-specific little ParaView tip. Something that might come in handy for a quick job check or for monitoring convergence. It’s particularly useful on remote machines &/or if you’re allergic to gnuplot.

Here it is:

You can read OpenFOAM monitor (.dat) files directly into ParaView using the Tecplot Table reader 🤫

I’m talking about plotting the output from functionObjects like forceCoeffs or surfaceFieldValue – i.e. tabulated scalar data. The kind of info that’s handy to take a quick peak at while a simulation is running or as a visual convergence check after the fact.

I usually use it on remote machines, where I’ll bring up a client-server ParaView & have a quick check – most definitely not watching convergence, no way, not me.

You could do the same thing in gnuplot – but it’s nice to have options, especially if they don’t require Googling the (gnuplot) commands that I forgot, again.

How-To

Let’s take the output of a pressure monitor made using patchAverage via surfaceFieldValue as our example.

We’ll get a data file written to:

$FOAM_CASE/postProcessing/patchAverage/0/surfaceFieldValue.dat

filled with our lovely tabulated data, looking something like this:

If you open that file directly in ParaView it won’t quite know what to do with it & ask you to choose your preferred reader:

Choose Tecplot Table Reader, click OK & then we’ll need to give it some info about our input file.

In this case (see sample of the data file above), we have:

• 5 lines in our header (those starting with # )
• our column names are on line 4 (note that it’s 0 indexed)
• we need to skip 1 leading # to get the column names right

Leaving the max. number of records at 0 will read in the whole data file.

Click Apply & that should do it. Change the default spreadsheet view to a line chart view, make sure the data is visible (click the eye in the pipeline browser) & you should have yourself a line chart.

You can customise things to your hearts content – add legends and titles, turn series on/off, mess with fonts & colours etc.

You can pan & zoom around using the mouse (just like you would in 2D mode) & reset the zoom using the usual buttons.

If you want to ignore the start of the file, then just increase the number of header lines in the reader & it’ll skip that many lines.

If you’re monitoring a live run, then right-click the data in the pipeline browser & click Reload Files to re-read the data (the settings for the chart & reader are sticky – they don’t reset when you do this).

Gotchas

There’s one gotcha: it doesn’t work with vector data.

For example, if you’re monitoring a vector field or force/moment components, then the reader will trip over the parentheses in the data file 🙈

You can easily strip them out to make it compatible, just don’t do it to a live/running data file – you’ll really confuse things.

A quickie

There you go, a quick ParaView tip that might come in useful one day. The quick tip format seems to be quite popular, but if I’m wrong, let me know.

I struggle with the ParaView emails a bit, so what do you want to know? Is there anything specific I can help you with?

Let me know, I’ll add it to the list & you’ll be making these emails better for everyone 🙏

Until next week, stay safe,