# How to learn CFD (For Absolute Beginners)

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 December 26, 2020, 17:43 How to learn CFD (For Absolute Beginners) #1 New Member   Fehmi Join Date: Dec 2020 Posts: 1 Rep Power: 0 Before starting, I would like to state that I am a new member and this is my first post, so if the post is somehow inappropriate, I will remove it. Hello everyone, I am a 4th year undergrad student and I want to start to learn Computational Fluid Dynamics. I am interested in flow in porous media. However, the books I have found (even the ones that claim to be for total beginners) introduce the concept with overwhelming mathematical equations. After not understanding for quite a while, I decided to give a shot to ask here for your advices. Can you suggest me a book/tutorial/lecture to learn CFD from scratch? I count on my mathematical knowledge (Both calculus and differential equations), however, I might be a little weak on vector calculus and fluid mechanics. Thank you.

 December 27, 2020, 15:21 #2 New Member   Marcos Gutiérrez Join Date: Dec 2020 Posts: 8 Rep Power: 5 Hi Fehmi, Before to dig into CFD, take a look into the theory of Fluid Mechanics. Any book about that of the "for dummies - A Wiley Brand" series is a good start. In a few weeks in www.tablet-school.com we will launch an eBook and eLearning to cover the CFD from the fundamental concepts, basic equations, making a CAD model, simulating in OpenFOAM, displaying the results in Paraview and analyzing the results. We will cover at the beginning only the internal flow in pipes and the spray of fuels. Best wishes Marcos gigila likes this.

December 27, 2020, 15:31
#3
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Filippo Maria Denaro
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Quote:
 Originally Posted by fozba Before starting, I would like to state that I am a new member and this is my first post, so if the post is somehow inappropriate, I will remove it. Hello everyone, I am a 4th year undergrad student and I want to start to learn Computational Fluid Dynamics. I am interested in flow in porous media. However, the books I have found (even the ones that claim to be for total beginners) introduce the concept with overwhelming mathematical equations. After not understanding for quite a while, I decided to give a shot to ask here for your advices. Can you suggest me a book/tutorial/lecture to learn CFD from scratch? I count on my mathematical knowledge (Both calculus and differential equations), however, I might be a little weak on vector calculus and fluid mechanics. Thank you.

Learning CFD requires to have a good background in fluid mechanics and mathematics (PDE, vector calculus, etc), as well as some skill in a programming language.

Otherwise you will not learn CFD but you will be only one of the users of a commercial CFD code.

 December 27, 2020, 19:24 #4 Senior Member   Kira Join Date: Nov 2020 Location: Canada Posts: 435 Rep Power: 8 Hello. I second Filippo's sentiment. Without truly understanding the equations we are using when performing CFD analyses, we are merely software operators and not truly engineers. So a good background in fluid mechanics, aerodynamics and even heat transfer would be very beneficial. I recommend John Anderson's CFD textbook, Computational Fluid Dynamics: The Basics with Applications. There are also many CFD course slides available on the internet. Other than getting comfortable with theory, you can try to replicate results obtained from scientific/research papers, or ask a professor if he/she has any CFD work you could do for practice. You can also do the tutorials provided by ANSYS, as they cover a wide range of programs and techniques. One final thing to keep in mind; play around with the various programs, including ANSYS Fluent, Design Modeler, ICEM CFD and CFX. Some people prefer one or the other (I use ICEM and CFX, haven't touched Fluent much), but being familiar with all the programs and their respective strengths/weaknesses will also be good. FMDenaro and Dr Youssef Hafez like this. Last edited by aero_head; December 28, 2020 at 01:42.

 January 3, 2021, 19:41 #5 New Member   q Join Date: Sep 2020 Posts: 19 Rep Power: 5 You don't need to care about suggestions like "you need to be good at bla bla bla before you even touch cfd". These kind of advices you will usually get from old advanced folks who had forgotten where they were when they first encountered CFD. Apart from that your PhD will last 5 yers so you will not be able to learn everything - it is not even necessary. What is more funny you don't need to know techniques for solving pde's to use CFD which is obvious but you don't even need to know them to develop your own CFD code! The truth is, initially, no one was a specialist even professors on this forum and they all were dumb in this field years ago. Another truth is that there is no single book that give you a complete knowledge, some of them are hard but very accurate some of them are too general. Yet another truth is you need to read anything what you can possibly grab in you hands (including articles since they provide a condensed knowledge) however you will probably not understand a bit at first, but after reading and discussing that matter with other folks hundreds times, at some point you will be striken by a bright path that connects all the puzzles. The most important thing is not to resign be patient and start to develop the feelings for fluid mechanics! L Nastalek, aerosayan, moni91 and 2 others like this. Last edited by q__; January 3, 2021 at 20:43.

January 4, 2021, 02:15
#6
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Sayan Bhattacharjee
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Quote:
 Originally Posted by fozba Before starting, I would like to state that I am a new member and this is my first post, so if the post is somehow inappropriate, I will remove it. Hello everyone, I am a 4th year undergrad student and I want to start to learn Computational Fluid Dynamics. I am interested in flow in porous media. However, the books I have found (even the ones that claim to be for total beginners) introduce the concept with overwhelming mathematical equations. After not understanding for quite a while, I decided to give a shot to ask here for your advices. Can you suggest me a book/tutorial/lecture to learn CFD from scratch? I count on my mathematical knowledge (Both calculus and differential equations), however, I might be a little weak on vector calculus and fluid mechanics. Thank you.

Don't use books to initially learn CFD. Look up Youtube CFD tutorials for simple cases and try to get some experience using a CFD package from ANSYS, COMSOL, Su2 etc. Simple cases of CFD would be "CD nozzle flow", "channel flow", "flow over aerofoil" etc. Then you can go back to the books and study the mathematics in detail. Spending time on books initially to learn the basics of CFD is a bad idea.

January 4, 2021, 02:52
#7
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Sayan Bhattacharjee
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 Originally Posted by FMDenaro Learning CFD requires to have a good background in fluid mechanics and mathematics (PDE, vector calculus, etc), as well as some skill in a programming language. Otherwise you will not learn CFD but you will be only one of the users of a commercial CFD code.

I respectfully disagree. What you mentioned is required to become an expert in CFD; not learn the basics. I have observed that students learn basics of CFD better if they're instructed to use a commercial software package like ANSYS. Most engineers will only use commercial packages. Programming skills are not necessary for beginners. If they know MS-Excel, they can validate their results.

January 4, 2021, 03:52
#8
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Filippo Maria Denaro
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 Originally Posted by aerosayan I respectfully disagree. What you mentioned is required to become an expert in CFD; not learn the basics. I have observed that students learn basics of CFD better if they're instructed to use a commercial software package like ANSYS. Most engineers will only use commercial packages. Programming skills are not necessary for beginners. If they know MS-Excel, they can validate their results.
The key is to discern from the term learning CFD and using CFD. The former means to learn the topics you can read in any CFD textbook, the latter is to read the Fluent user guide and some youtube tutorial.
The initial question is about how to learn.

January 4, 2021, 03:55
#9
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Filippo Maria Denaro
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 Originally Posted by q__ You don't need to care about suggestions like "you need to be good at bla bla bla before you even touch cfd". These kind of advices you will usually get from old advanced folks who had forgotten where they were when they first encountered CFD. Apart from that your PhD will last 5 yers so you will not be able to learn everything - it is not even necessary. What is more funny you don't need to know techniques for solving pde's to use CFD which is obvious but you don't even need to know them to develop your own CFD code! The truth is, initially, no one was a specialist even professors on this forum and they all were dumb in this field years ago. Another truth is that there is no single book that give you a complete knowledge, some of them are hard but very accurate some of them are too general. Yet another truth is you need to read anything what you can possibly grab in you hands (including articles since they provide a condensed knowledge) however you will probably not understand a bit at first, but after reading and discussing that matter with other folks hundreds times, at some point you will be striken by a bright path that connects all the puzzles. The most important thing is not to resign be patient and start to develop the feelings for fluid mechanics!

Old discussion, cfd expert vs. Cfd user ... Anyone should be aware about the difference. But the idea the CFD is nothing but turning on a TV is fool...

January 4, 2021, 06:05
#10
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Quote:
 Originally Posted by q__ You don't need to care about suggestions like "you need to be good at bla bla bla before you even touch cfd". These kind of advices you will usually get from old advanced folks who had forgotten where they were when they first encountered CFD. Apart from that your PhD will last 5 yers so you will not be able to learn everything - it is not even necessary. What is more funny you don't need to know techniques for solving pde's to use CFD which is obvious but you don't even need to know them to develop your own CFD code! The truth is, initially, no one was a specialist even professors on this forum and they all were dumb in this field years ago. Another truth is that there is no single book that give you a complete knowledge, some of them are hard but very accurate some of them are too general. Yet another truth is you need to read anything what you can possibly grab in you hands (including articles since they provide a condensed knowledge) however you will probably not understand a bit at first, but after reading and discussing that matter with other folks hundreds times, at some point you will be striken by a bright path that connects all the puzzles. The most important thing is not to resign be patient and start to develop the feelings for fluid mechanics!
Your claims are a bit strange. I believe that the questioner is not interested in learning cfd like a monkey. There is nothing wrong with learning from experienced people or taking advice from them.

Regards
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January 4, 2021, 06:29
#11
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q
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 Originally Posted by Eifoehn4 Your claims are a bit strange. I believe that the questioner is not interested in learning cfd like a monkey. There is nothing wrong with learning from experienced people or taking advice from them. Regards

Certainly, is good to have infinite amount of time for spending years in mastering all the available numerical methods for pde's or anything else sitting on post-doc or full-time job at the university. But there are people that will not get the money from their mom or university and need to make progress fast. It is possible and efficient to learn from templates because initially no one knows what need to be known. If you think differently that is ok but I am not interested in that, since I have not created this thread.

 January 4, 2021, 06:42 #12 Senior Member     - Join Date: Jul 2012 Location: Germany Posts: 184 Rep Power: 14 It's more the other way around. With your way of learning you will waste much more time at the end of the day. sbaffini, haydena and aero_head like this. __________________ Check out my side project: A multiphysics discontinuous Galerkin framework: Youtube, Gitlab.

 January 4, 2021, 07:31 #13 Senior Member     Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,168 Blog Entries: 29 Rep Power: 39 With absolute lack of context it is difficult to give the proper advice, as the diverging point of views emerged here have, probably, shown. What are you going to learn CFD for? Also, how does that fit your study path? Is it a complement, a curiosity, a mandatory deviation or something you want to be good at? But, for sure, the only way to be good at something is to spend time on it. Even if you are some savant, the only way to know everything that has been produced in a field is to spend time reading it (even if you are very fast digesting it). You set your own pace, timing, etc. but there is no escape from this. But if you hate spending time on a subject, there are chences that you would better invest that time on something else. When I started university, coming from classical studies, I couldn't tell apart a general polynomial from a simple line. I had my epiphany and started working on it... I still work on it. Ask whoever you know that is good at something how that worked for them. No matter if it is CFD, cooking, parkour, driving, tasting wine or whatever. They spent time on it. Period. For example, I had exposure, during my studies, to both solid mechanics and FEM software to solve related problems. Do I really understand the matter? Hell, no! I couldn't be more obtuse on solid mechanics despite having top grades on all the related courses. Why? Because I spent zero time on it. But you don't have to be afraid of the progresses you make, of how much you understand, of the time it takes. If you do you are already wasting your time. Treatments of porous media are kind of delicate/sophisticate on the math side, so I wouldn't suggest to start there. As others mentioned, the classical path PDE, Fluid Mechanics, Numerical methods, CFD has been tested so many times to be effective and rewarding, with anyone following it being happy with the accomplishment, that it would certainly deserve a shot, if this is what you want to do. Also, honestly, there is no chance you can really understand any CFD concept without knowing the underlying concepts. In conclusion, spend on the subject a proportionate amount of time with respect to the goal you have. The better you want to be, the farthest away from it you should start (e.g., is your vector calculus solid enough?). FMDenaro, aero_head and Dr Youssef Hafez like this.

January 4, 2021, 08:06
#14
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Paolo Lampitella
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 Originally Posted by q__ Certainly, is good to have infinite amount of time for spending years in mastering all the available numerical methods for pde's or anything else sitting on post-doc or full-time job at the university. But there are people that will not get the money from their mom or university and need to make progress fast. It is possible and efficient to learn from templates because initially no one knows what need to be known. If you think differently that is ok but I am not interested in that, since I have not created this thread.
It is indeed true that having time to spend on something means having the related money to do that, but the need of time to master a subject remains true as well.

There are countries where that time at university has unreasonable costs, but others where it is pretty much affordable by anyone. There are some degrees that oblige you to spend time on subjects that you will never need and some others that instead allow more focusing early during the path.

But nothing can be good, fast and easy/cheap at the same time.

 January 4, 2021, 08:09 #15 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,815 Rep Power: 73 Have a look to the questions on this forum, for example just during the 2020. How many questions are due to the fact the people think to learn CFD simply by clicking some options in their GUI? aero_head and Dr Youssef Hafez like this.

 January 4, 2021, 08:39 #16 Senior Member     Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,168 Blog Entries: 29 Rep Power: 39 Forgot to mention the most important thing, the suggestions I have for books: 1. Fluid Mechanics by Pijush and Kundu (the easy one) 2. Vectors, Tensors and the basic equations of fluid mechanics by Aris (the needed one) 3. A first Course in Turbulence by Tennekes & Lumley + Turbulent Flows by Pope (the necessary entry points for turbulence) 4. Fundamentals of Engineering Analysis by Moin (where numerics start) 5. Computational Fluid Mechanics and Heat Transfer by Anderson (sufficiently easy all around) 6. Numerical Computation of Internal and External Flow by Hirsch (still easy all around, different perspective and probably more modern) 7. Computational Fluid Dynamics by Blazek (almost anything you need to know for serious and practical CFD, except pressure based methods) 8. Computational Methods for Fluid Dynamics by Ferziger et al. (a good reference for pressure based methods but not very well written for beginners) 9. The Finite Volume Method in Computational Fluid Dynamics by Moukhalled et al. (seems a very good and comprehensive reference for pressure based methods) Note how there are no books on other fields like PDE, calculus, etc., as the minimum requirements are covered in these books as well (typically in Appendices). Hopefully, you will be able to also attend a course on each one of these topics. q__ and aero_head like this.

 January 4, 2021, 10:31 #17 Senior Member   Joern Beilke Join Date: Mar 2009 Location: Dresden Posts: 508 Rep Power: 20 You should know, what you want to become in the future. We have the EXPERTS who read all the books, know all the equations and turbulence models, everything about numerical schemes and how a good mesh has to look like ... But they never created a mesh more difficult than a 100x100x100 box, don't know how to use a CAD program and never set up a real world simulation. They also have no idea how to solve a engineering problem by using CFD. All their thinking is just differential equations. On the other side there are engineers with a solid understanding of the physics which simply start to use a CFD code and are able to solve difficult problems. My suggestion is to start playing around with a CFD code (maybe OpenFOAM) and try to understand what it does. Run a tutorial and do some modifications. Compare it with results from the literature and ask the community when you can not find the answer yourself. CFDfan likes this.

January 4, 2021, 11:32
#18
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Filippo Maria Denaro
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 Originally Posted by JBeilke You should know, what you want to become in the future. We have the EXPERTS who read all the books, know all the equations and turbulence models, everything about numerical schemes and how a good mesh has to look like ... But they never created a mesh more difficult than a 100x100x100 box, don't know how to use a CAD program and never set up a real world simulation. They also have no idea how to solve a engineering problem by using CFD. All their thinking is just differential equations. On the other side there are engineers with a solid understanding of the physics which simply start to use a CFD code and are able to solve difficult problems. My suggestion is to start playing around with a CFD code (maybe OpenFOAM) and try to understand what it does. Run a tutorial and do some modifications. Compare it with results from the literature and ask the community when you can not find the answer yourself.

1) Grid generation is somehow a different a specific topic, often people doing grid generation do not work then on the CFD problem. Do not introduce grid generation in this discussion.

2) Everything in CFD is within the numerical approximation of differential (and integral) equations topics.

3) Be aware to not generalize your ideas,ì; despite the fact that in accademy the flow problems are often simple in the geometry, the physics is complex. And who works on academic problems is also often acquainted with experience on real flow problem.

4) Ignorance is ignorance. You can mask that behind the use of a CFD software but being good in physics is not sufficient to run a CFD code and getting other than some wonderful coloured plot. This presumption was already spread around the world in 80s and caused many problems so that the research in CFD turns back to fundaments.

 January 4, 2021, 13:36 #19 Senior Member   Joern Beilke Join Date: Mar 2009 Location: Dresden Posts: 508 Rep Power: 20 The important point is not from which end you start, but where you end up. Who is more useful for a society? The man who knows everything about a hammer or someone who can actually use it. Someone who thinks to know all about viruses or someone who can treat ill people?

January 4, 2021, 13:47
#20
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Filippo Maria Denaro
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Quote:
 Originally Posted by JBeilke The important point is not from which end you start, but where you end up. Who is more useful for a society? The man who knows everything about a hammer or someone who can actually use it. Someone who thinks to know all about viruses or someone who can treat ill people?

wrong statement... there exists a guideline in science, going form basic and fundamental research through applied science and technology. Thinking of contrapositions among these branches is a poor view of the reality.
A man using a hammer exists since the born of mankind. But you stated no distinction between a man using a stone and a man using a modern hammer tool. Who produced the modern advanced hammer ?

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