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FreeCAD does many amaz­ing things, allows us to cre­ate all kinds of geome­tries and assem­blies, but we can also use FreeCAD for analy­sis of the things we make. One fas­ci­nat­ing approach is Com­pu­ta­tion­al Flu­id Dynam­ics or CFD.

CFD is essen­tial­ly a tool to show how flu­ids inter­act with objects. You could mod­el and assess water flow­ing through a pipe, or a boat in the sea, or for fly­ing objects, air­flow over a part and much more. Of course CFD can also help analyse and per­form com­plex cal­cu­la­tions on data so it’s not uncom­mon to use CFD to work out the drag coef­fi­cient of an object or it’s cen­tre of pres­sure and much more.

It’s fair to say CFD is a com­plex area and one that the author is only just begin­ning to scratch the sur­face of. There­fore this arti­cle isn’t a tuto­r­i­al on CFD direct­ly, rather we’ll look at installing the Cfd­OF work­bench which requires the instal­la­tion of some oth­er tools on your sys­tem, and then point at some use­ful tuto­ri­als online for you to begin your CFD learning.

The Cfd­OF work­bench pro­vides an inter­face for numer­ous oth­er open­source soft­ware’s which com­bine to com­plete the CFD process. These include some mesh­ing tools. CFD is com­mon­ly per­formed on meshed objects with the tar­get object placed in a con­tain­ing geo­met­ric space, a large cuboid or cylin­der per­haps. A good anal­o­gy is the con­tain­ing space is like a vir­tu­al wind tun­nel, although you aren’t lim­it­ed to just air! The whole envi­ron­ment gets turned into a mesh and often with­in the mesh var­i­ous dif­fer­ent mesh set­tings are used (called mesh refine­ments) so that ulti­mate­ly you get more detail around the sur­face of the test object. There­fore mesh­ing is impor­tant and there are numer­ous mesh pack­ages for dif­fer­ing mesh­ing approach­es built in to a suc­cess­ful Cfd­OF work­bench install.

Anoth­er com­po­nent piece of open­source soft­ware used by the Cfd­OF work­bench is Open­FOAM. Open­FOAM is the very heart of CFD oper­a­tions and is a com­plex piece of soft­ware that can per­form a wide range of com­plex flu­id flows. It’s not just capa­ble in terms of things we might obvi­ous­ly think of as com­pu­ta­tion­al flu­id dynam­ics, such as water/gases/air but can also solve prob­lems involv­ing chem­i­cal reac­tions, heat, mag­net­ic fields and more. It’s an incred­i­bly ver­sa­tile and com­plex bit of kit that gets used, often stand alone, in all man­ner of sci­en­tif­ic and aca­d­e­m­ic environments.

Final­ly there is also a piece of soft­ware called Par­aview. Par­aview is a post proces­sor that, in the case of the CdfOF work­bench, can allow you to visu­alise and analyse case data cre­at­ed with Open­FOAM. It has huge depth and com­plex­i­ty and can per­form and cre­ate all man­ner of visu­al­i­sa­tion as well as per­form­ing cal­cu­la­tions to aid fur­ther analy­sis of your models.

So we need to get all these com­po­nents installed and con­fig­ured. One advan­tage of the CdfOF is that it auto­mates some of the set­up for us using dock­er and a dock­er image. In the FreeCAD doc­u­men­ta­tion there’s instruc­tions for installing CdfOF on Win­dows and Lin­ux (also Mac but sup­port there is vari­able), also it’s worth read­ing the notes on the Cfd­OF work­bench repos­i­to­ry which are also includ­ed in the Addon man­ag­er list­ing. We opt­ed to install CdfOF on a machine run­ning stock Debian 12, run­ning the X11 win­dow­ing sys­tem, and we installed it with the FreeCAD ver­sion 1.0 app image. 

To begin, open the FreeCAD app image (if it’s the first time you might need to right click on the app image file, select prop­er­ties and then under the per­mis­sions tab you might need to tick the is exe­cutable box).

Once FreeCAD has opened, install the Cfd­OF work­bench in the usu­al way. Click tools-addon man­ag­er and then select and install the Cfd­OF work­bench. Once the Cfd­OF work­bench is installed and you’ve restart­ed FreeCAD, you can then click edit – pref­er­ences and you should see a Cfd­OF tab appear in the pref­er­ences dia­logue. Select the Cfd­OF tab. You will see that it has numer­ous input box­es into which you can set paths to the direc­to­ries where the var­i­ous oth­er pieces of soft­ware are installed. If you leave these blank then Cfd­OF work­bench will use the default most com­mon loca­tions for the install loca­tions which worked per­fect­ly for us. So on our Debian 12 machine we used a the ter­mi­nal appli­ca­tion to first run an update to update all pack­ages with

sudo apt update

we then ran;

sudo apt-get install openfoam

and after Open­FOAM had installed we ran;

sudo apt-get install paraview

to install Paraview.

For the rest of the set­up we need­ed to install dock­er. In the Cfd­OF FreeCAD doc­u­men­ta­tion page there is a link sup­plied to a guide to installing up to date dock­er on Debian so we sim­ply fol­lowed these steps. https://www.linuxtechi.com/install-docker-engine-on-debian/

One thing that slight­ly tripped us up was that not only do we need to add our user­name to the dialout group, but we also need to log out and log back in to our com­put­er hav­ing done so! Again in a ter­mi­nal we used;

sudo usermod -aG dialout “YOURUSERNAMEHERE” 

and then (after hav­ing some prob­lems we even­tu­al­ly remem­bered to) re login to the com­put­er. Now with dock­er installed and Open­FOAM and Par­aview installed we can fire up the FreeCAD app image, move back to the Cfd­OF pref­er­ences tab and then click the Install Dock­er Image but­ton. Anoth­er quick tip is that it can be use­ful to have the report view pan­el open in FreeCAD at this point so you can see mes­sages relat­ing to the dock­er con­tain­er and any poten­tial prob­lems . To open that pan­el you can click view – pan­els and then check the Report view box. There is also a small report win­dow if you scroll to the bot­tom of the Cfd­OF pref­er­ences tab which yields use­ful infor­ma­tion about the install process. Even­tu­al­ly you should be reward­ed with a com­ple­tion mes­sage indi­cat­ing the dock­er image down­load has been successful.

Final­ly before div­ing head­long into your CFD career it’s worth click­ing the Run depen­den­cy check­er but­ton in the Cfd­OF pref­er­ences dia­logue. This should hope­ful­ly report that every­thing is installed correctly.

If you are new at CFD then be pre­pared for quite a lot of learn­ing to even get any tan­gi­ble out­put! How­ev­er, there are heaps of guides and tuto­ri­als out there to help you along the way. Whilst we’d urge you to look around, the first tuto­r­i­al we worked through was this Youtube tuto­r­i­al walk­ing through set­ting up an analy­sis of water in a broad­ly L shaped square sided tube. It def­i­nite­ly intro­duced the gen­er­al process and order of dif­fer­ent oper­a­tions. This is the first video in a long series of tuto­ri­als com­piled into a playlist. Jump­ing to episode 6 in the same series the tuto­r­i­al cov­ers flow­ing air over a car design which was very use­ful for the authors par­tic­u­lar areas of inter­est. After a cou­ple of evening from zero knowl­edge of CFD the author got to the point of cre­at­ing a crude analy­sis of a Bal­lute para­chute design with 6 m/s air­flow over it. Whilst the author is con­tin­u­ous­ly dis­cov­er­ing errors in approach and dis­cov­er­ing bet­ter ways to mesh and sim­u­late, it does show that you can begin this jour­ney with very lit­tle under­ly­ing knowledge!

Final­ly, the Cfd­OF work­bench has an excel­lent devot­ed sec­tion on the FreeCAD forum. It’s def­i­nite­ly worth read­ing through as many posts there as you can as it’s a great source of valu­able infor­ma­tion by oth­er peo­ple on the CFD path!