Hey there,
It’s Robin from CFD Engine & it’s three tiny tips time again – nothing long-winded, just three OpenFOAM tips that you might find useful.
This time out we have two little helpers (especially for those of us that get command-line anxiety) & a handy little functionObject.
Let’s go…
fieldAverage
Have you ever felt the need to average a flow field over part of a run? Maybe it’s a time-average for a transient simulation, or the mean of a steady-state case that’s not quite so steady.
fieldAverage to the rescue – a functionObject that calculates the mean of any of our fields during the solve.
For example, the snippet below would average the U & p fields, of a steady-state simulation, starting at 1000 iterations, writing out their mean equivalents (including the vector components) at every subsequent write.
fieldAverage
{
type fieldAverage;
libs (fieldFunctionObjects);
timeStart 1000;
writeControl outputTime;
fields
(
U
{
mean yes;
prime2Mean no;
base time;
}
p
{
mean yes;
prime2Mean no;
base time;
}
);
}
You can’t use it with postProcess as it does the averaging whilst iterating, it’s not magic. But just add it to the functions sub-dictionary of controlDict (as you would any other functionObject) & plot some lovely averaged fields.
Check out the documentation for more options. They include recording the variation about the mean (prime2mean), the ability to apply a window to give a rolling mean and a handful of settings to control when it starts/stops and what to do in the event of a restart.
foamListTimes
For many people (particularly new users) their OpenFOAM headaches often stem from a lack of confidence on the command-line. If you’ve been on Windows forever & you’re suddenly faced with doing stuff on the command-line, it can get a little tense.
There are a few OpenFOAM commands that are essentially wrappers around command-line operations, that try to make common operations a little friendlier / easier to use.
An example is foamListTimes which makes it easier to work with multiple time directories. It works in parallel (add -processor) and can be used to both list & remove directories.
For example, the following:
foamListTimes -rm -time '7:' -processor -verbose
would delete the time directories (-rm), from time 7 to the end (-time '7:'), across all the processors (-processor) & let you know how it’s progressing (-verbose).
I’ve started using it more often & found it pretty handy when you have lots of time directories. It’s also easily readable which makes it a great choice for adding to scripts. When someone else (who’s not as handy as you on the command-line) picks up the script, it’s easy to understand what it does.
Whatever the case, be careful when deleting data, there’s no undo button on the command-line 😳
restore0Dir
The first time you run potentialFoam and realise that it writes to your 0 directory, you might decide to start keeping your boundary conditions safely tucked away in a 0.orig directory & copy it to 0 just before running instead.
restore0Dir simply blows away all your existing 0 directories & replaces them with a copy of 0.orig (including in all the processor directories, if you add the -processor switch). It also does some magic with #include files if you’re using the collated file format.
As with foamListTimes, it’s nothing you couldn’t do with a couple of Unix commands, but it’s handy & sits nicely in a run script.
It’s not a stand-alone command though, it lives in the RunFunctions script which I’ve mentioned before & which you need to source using:
. ${WM_PROJECT_DIR:?}/bin/tools/RunFunctions
Add that line near the top of your run scripts to make things like restore0Dir, runParallel & runApplication available for use.
Not to be confused with foamRestoreFields which does something similar, but different.
Over to you
That’s all folks – just three tiny tips – deleting time directories, restoring zero directories & averaging fields to help things make sense.
Did you know these already? Did I miss anything? Let me know what you reckon so that I can tailor future tips.
Likewise, if you’ve found a gem that you’d like me to steal share, then drop me a note & I’ll add it to the list.
Until then, stay safe,
