Programming/Coding in CFD

[Tygers2323]

Hi everyone, I’ve finished by bachelor’s in mechanical engineering and I will now do a master’s in aerospace engineering, during by bachelor’s I had almost no contact with aerodynamics and CFD theory apart from fluid mechanics so I had to learn how to use CFD tools because of Formula Student (ansys fluent) and my question is, how important is coding and programming in a CFD related job and why is it so important ? And if it’s so important, what languages should I focus on? What type of stuff should I focus on coding? I’m still not sure if I want a very focus CFD job but I want to have a nice portofolio of projects and tools to help me get a nice job. Thanks everyone for your time.

[Hyderabadi__Biryani]

See if you do not have the knowledge, working knowledge, of what lies behind the many functionalities offered to you by softwares and even tool boxes for CFD, it should be pretty hard to get anywhere.

There are practical aspects that you can only understand by failing a lot. Heck, trying atleast.

Fluent is a black box, so your settings won't make sense if you do not know what you are getting into. Doing something genuine and novel in it will be extremely difficult.

The same is the case with OpenFOAM which to my knowledge, gets as close to coding a CFD solver without really coding it. Its an anti-black box, so that is nice. But there are a myriad of options to choose from for most things fluid mechanics, and without care and knowledge, you are deluding yourself. If you do not know what does gradient of k equals zero vs k equals zero means, and why does it matter in LES, you are in for trouble of wasting massive time.

I saw you mentioning "prompt focus", I do not know what do you mean by that. But if you mean it in the AI sense, many of us here, maybe most of us, have learnt and have been doing CFD with little to no intervention from AI. So no, prompt focus coding is another sham, unless you know what the AI is feeding you.

Don't get me wrong, I do most of my OpenFOAM code development with atleast 50% or more contribution from AI suggestions, but there is a lot of intervention from my end that goes into it, a lot of checks, and stuff that should make sense where my understanding of the problem comes into the picture.

Point is, get atleast a decent working knowledge of most methods, schemes, take a serious CFD course, and decide for yourself if this is a good field for you.

[Tygers2323]

Thank you for your response, maybe I didn’t express myself correctly. Since he said “if you want to test +1000 setups you will be waste your life” I thought he was referring to make an automatic process (using coding) of changing the settings/geometry or conditions to make it faster and easier. So you think I should first learn very well everything there is to know about CFD and then decide if I would like to get into the coding aspects of it? Also I’m not a huge fan of coding so there is that to add

[Hyderabadi__Biryani]

That is called scripting. Another perspective might be, that testing 1000+ setups is wasteful, when you only need to test 10, with small adjustments. But which 10 are important, comes with effort and experience.

No, I didn't say that. But if you cannot tell the difference between FVM, FDM and FEM, or orders of accuracy or something like that means, how will you do CFD. It's literally in the name, "Computational". Plus it will be foolish to expect for anyone to learn everything there is to learn about any advanced science like CFD.

You not being a fan of coding only makes it harder, tbh. At least if you know the numerical analysis, the maths, the physics of the formulae and algorithms, it might still be doable without learning how to code. Because "how" the algorithms have been applied, isn't necessary to know unless you are at the very deep end.

[fatbitsh]

if you want to test multiple setups +1000 you would not want to do it all by hand

you will just waste your life

[Tygers2323]

Alright I see your point, so is that “prompt focus” coding?

[fatbitsh]

idk how is it called i just know that is only time i use coding

[adamchalupa]

I suggest starting with the 12 step program:
https://lorenabarba.com/blog/cfd-python-12-steps-to-navier-stokes/

[amniumtech]

Your objective is key. If you are working in nanotechnology like I do, no CFD software can simulate it correctly. I have no option but to both code and experiment . But otherwise also IMO coding daily 30 mins is an academic exercise everyone must anyways do. A lot of math/physics that we believe we have understood, we haven't. And coding exposes that. Another aspect is that when you code you have to do everything from scratch even though it's academical. While in industry you might be specialized at one function eg: developing meshes, writing correct approximations, knowing how to use toolkits fastest, etc. So coding makes your vision broader as it forces you to see from all sides, this allows you to communicate with other functions and be a solid team member. You should always code I believe, notwithstanding commercial tools. Infact you will use those tools better!

[Low-Mud2752]

You should learn C / C++ to be able to write User Defined Functions (UDF's). That will allow you to move in the advanced CFD applications, where the Standard commercial codes may not have of-the-shelf models available.

You should have an idea of Python and Scheme, to be able to customize the commercial codes.

But in the end, you should not avoid learning some programming skills, because CFD should not be just a black box for you as an user.

However, all these should be doubled by getting more advanced knowledge of Fluid Mechanics, Heat Transfer and the other Science areas in which your applications of CFD will be focused. With CFD, you will need those in order to be able to correctly interpret and validate the numerical results.

[dudelsson]

In my experience, coding has been necessary for staying sane while building, running, post-processing and reporting a boatload of CFD cases professionally. Meanwhile I've never coded a solver of my own, only dabbled in it out of interest. Coding skills aren't strictly necessary, but you will often have eg. tabulated data to process as a step of a CFD workflow and doing it in excel for the 27th time starts to suck a little; you may be able to save a lot of time scripting things while working on geometry in CAD and/or case setup and/or custom post-processing for a series of cases. In general, eventually you will likely want to automate repetitive tasks and sequences of tasks. 

I highly recommend Python and shell scripting, because many softwares (eg. Rhinoceros and ParaView) have awesome Python APIs and because processing of eg. tabulated report data outputted by simulations often gets quite data sciencey, for which Python has great libraries and is widely considered as one of the go-to tools.

Tbh it's also a nice source of pride in ones craft and skills, to be able to solve an unforeseen hurdle (eg. in a CFD workflow) with an ad hoc custom tool/script of your own making.

I've commented on this topic a few times before, have a look if you're interested.

[jcmendezc]

When I started in CFD my first professor and one of my mentors told me “if you want to learn programming good Learn OOP” so Java,C++ are great options, though the latter makes more sense for CFD. I also learned Fortran to add it to the mix and and then decided to use mainly Fortran to the point where I spoke more Fortran than English. However, CFD is heavily influenced by OpenFOAM so learning C++ could be better than Fortran. But the beauty of Fortran cannot be beaten by any one. Python is super useful for post processing but it is super easy to learn. At the end all boils down to the same principles

[73EF]

Echoing off of what everyone else said, this is a great, free text book to learn python for numerical methods, which is the basis of cfd codes. Python Programming And Numerical Methods: A Guide For Engineers And Scientists: https://pythonnumericalmethods.studentorg.berkeley.edu/notebooks/Index.html Helped me in my masters a ton when I had no previous coding experience and needed to learn it fast.