General questions about CFD

[Anonymous]

Hi guys,

I'm struggling a bit with litterature. I've been reading Autodesk CFD online manual and found that the software uses finite element method instead of finite volume method. I don't understand if the equations are the same for each method or not. I mean, is the energy equation or Navier Stokes equations and all governing equations the same for each method?
Can anyone give me a hand so I can understand more easily the litterature?

P.s: @frederic.gaillard.7 , I've some banger news to tell you. 
Since I can't DM you, please send me an e-mail to 1150658@isep.ipp.pt

Thanks.

[frederic.gaillard.7 · Accepted solution]

Hey Dre, 

Nice to heard from you again.

Fortunately governing equation doesn't really change : Mass, linear momemtum et energy conservation princple are universal concept and they stay the same at a macroscopic scale. What is changing, however, is the way that we mathematically solved those 3 equation.  Numerical method are used to solve the governing equation because most of them dont have analytical solution (i.e. Navier Stokes equation) Numerical method require to discretize the computational domain into several element and the whole time process into small fragment of time. So if you are using FEM or FVM the equation will differ mathematically speaking but the physic behind them will not change. 

Even if it's a interesting subject, I don't want to dig further into that field because it will become complex very quickly, but internet is full of ressource to help you with this task. 

Finite Element vs Finite Volume 

method for solving PDE 

Discretization (check the section see also it will refer you to FDM & FVM page) 

Hope it answers to your question 
Fred

[Anonymous]

Hi Fred,

Thanks for the quick answer. I'm sorry, I've been a bit "off the grid" 😉
That's what I've found too. My main problem is to translate some words to my language (I'm portuguese), so sometimes it's hard to understand some concepts and sometimes I found myself asking if I actually did understand the information correctly or not. 
Everything you said was what I found and I'm happy for realising that I understood the literature correctly. 
I'm reading "An introduction to computational fluid dynamics : The finite volume method" by H.Versteeg
The "finite volume method" aproach had my alarms go off because I found in the online manual that Autodesk CFD uses FEM. So at that point I was confused about the governing equations and wasn't sure if they are all the same. 
But basically mass conservation equation and etc... will remain the same for FEM and FVM right? However, the discretization method will be different for each method.
I know that this is a very complex subject, but I'm willing to do the extra effort to understand it and be confortable with it.

[frederic.gaillard.7]

Hello Dre, 

An Introduction to Computational Fluid Dynamics wrote by HK Versteeg and W Malalasekera is a good book to start. It will give you a good overview of CFD fields and certainly will make a solid ground for the theory and the vocabulary as well. If you want to have a deeper understanding of the discretizational algorithm used in the finite volume method, it might worth to read a book who tackle this specific subject. But for a first reading the one that you select is largely suffisant. 

Good Luck 
Fred

[Anonymous]

HI @frederic.gaillard.7 ,

It's a good book. I'm having some progress with it and also with the one you mentioned! 
However, An Introduction to Computational Fluid Dynamics wrote by HK Versteeg and W Malalasekera is a book focused on finite volume method. For my master thesis I must focus on FEM because Autodesk CFD is based on it. But as far as I understand I can use this book to study the basics of CFD and when it comes to the discretization methods and solvers I should focus more on FEM since that's the major difference between FEM and FVM right?

[frederic.gaillard.7]

Hello Dre, 

i think you understand it quite well. 

if there is anything that i can help you with, don't hesitate, i will try to the best of my habilities.

Fred

[Anonymous]

@frederic.gaillard.7  Thanks!!

I'll try to read those 2 books ASAP. It doesn't take that long because half of it is talking about aerofoils and some other stuff that don't matter to me yet. 
Anyway, thanks for the help! The only thing I'm having trouble is translating some terms, but I'll do it with the help of my teachers 😉 

Good luck friend.