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 September 21, 2012, 14:13 #2 New Member   dking Join Date: Aug 2012 Posts: 12 Rep Power: 7 Modeling software is used to create the geometry of the problem, and knowledge of CAD will help when you work with complex models. A mesh is used to represent the geometry in order to solve the equations of motion (Navier Stokes, which is like F=ma for fluids). There is no known solution to the continuous, full set of equations so they must be "discretized" and/or simplified. You may be able to follow some CFD tutorials and match their results, but before you start making your own, you should know basic fluid mechanics (and heat transfer). Before you can learn fluid mechanics you should know Calculus -> Ordinary Differential Equations -> Mechanics (static and dynamic) then, Fluid Mechanics -> Heat Transfer, with Partial Differential Equations/Linear Algebra/Numerical Methods being used in CFD in some form. If you are interested in fluid mechanics I recommend watching a few of these videos -> http://web.mit.edu/hml/ncfmf.html They are a good introduction and show some cool/non-intuitive behavior of fluids.

September 21, 2012, 14:43
#3
Member

Yon Han Chong
Join Date: Jun 2012
Posts: 77
Rep Power: 7
Quote:
 Originally Posted by ben1793 I have a lot of experience with 3D modelling software such as solidworks and autodesk inventor and love using the software, is 3D modelling software used much when using CFD?
I use a 3D modelling software (mainly NX) to draw out fluid domain i.e. you receive a solid model but it is the fluid between the solid you want to model using CFD so you have to create a fluid domain out from the solid. However, lots of people who is doing CFD will ask a 3D modeller to do that job for them as learning a 3D modelling software takes time.

Quote:
 Originally Posted by ben1793 I understand now that you create a mesh when running tests on a CFD program, does this mesh have to be made even if the model is pulled in from a 3d modelling software?
Yes. 3D modelling software will use equations to approximate lines and surface (you can call it analogue) but in CFD everything is digital (i.e. approximation using discrete small cells like a digital TV). Basically, creating discrete cells from analogue geometry is meshing. You could do meshless CFD but that is not very common and it is a whole lot of other discussion.

Quote:
 Originally Posted by ben1793 Does CFD involve a lot of maths and if so where is this math used because I thought the whole point of the CFD software was for it to do all the maths for you (I love maths and hope CFD uses a lot of it but I ask because I am curious)
If you are going to write a CFD code for practice there are many textbooks on CFD which will discuss about this. However reading fluid dynamics or heat transfer textbook could be a better option before learning CFD because if you do not understand what you are trying to model you are going to have a hard time understanding why we do things in certain ways in CFD.

Quote:
 Originally Posted by ben1793 I have heard a lot about different types of CFD (programs?) such as FLUENT, openFOAM and others on this forum, but I do not understand what exactly are these programs, do they not all follow the same principle and are just different variations of the same software?
90% of the time most of the popular CFD codes (FLUENT, openFOAM, CFX) will produce similar results. openFOAM is an open source code but others you have to pay license fees. Generally it takes times to learn a software so once one is starting to use a particular software he/she tend to stay with it. Most popular one is FLUENT but its license is probably the most expensive in the industry but it might be cheap in academy. Good marketing strategy, isn't it?

Quote:
 Originally Posted by ben1793 What do I need to learn before I start using CFD, on other posts I have seen some people saying c++ is needed (why is this?) and also if math is needed could you please tell me what type of math (matrix algebra, differential equations, calculus?)
When the computers were getting fast enough so that CFD can be useful in real situations Fortran was the people's choice for scientific programs. It is still popular because it is simple to learn and can generate efficient scientific programs. That's why there still are lots of CFD codes written in Fortran.

C was and still is a popular computer language for general programming and UNIX is written with C. People started to think that if I was going to learn just one language I would like to learn C because I may not be doing scientific programming for rest of my life.

Then C++ was introduced. It is an object-oriented language which basically means forcing people to check their coding more rigorously. This reduces human errors hence you can write longer codes with lot more people with less human errors. For this reason, as CFD codes got more complicated, people start to think it is a good idea to use C++ to write CFD codes (e.g. openFoam). Also it will be looking good on your CV when you apply for jobs if you say you know C++ ).

However, they are not the only program languages you will find in the programming community and most of people will learn multiple computer languages. Also you can mix different languages in a code so choice of languages will become less important. Therefore choose one you would like to learn and see whether you can find help if you get stuck because you will get stuck.

[QUOTE=ben1793;383014]And my final question (for now) is, is there any free CFD software such as openFOAM that can run on windows or is it all on linux?[\QUOTE]

I am not a openFOAM user but I think there is a MS windows version.

I hope that this will be useful for you somewhat.

Last edited by yonchong; September 21, 2012 at 17:01.

 September 21, 2012, 16:34 #4 Member   Ben Join Date: Sep 2012 Posts: 40 Rep Power: 6 Thank you for the very helpful replies and link (much more detailed than what I was getting on yahoo answers ) I have started looking deeper into fluid dynamics and heat transfer and also will look into programming languages very soon, but do you think it is possible for me to have a go at openFOAM before learning a lot about programming and heat transfer just so I get a feel of things or is it necessary to have a good understanding of all the above to use even the basics of CFD? Again, I just want to say thank you for taking the time to help a new guy out

 September 21, 2012, 16:51 #5 Member   Yon Han Chong Join Date: Jun 2012 Posts: 77 Rep Power: 7 Sounds like you want to run a CFD code straight away. There is no harm running a CFD code. There is a tutoring for a complete beginner for openFOAM. However, you probably won't enjoy very much becasue you are not sure why you are doing them. The problem with CFD is like any complex tool you can easily mis-use it. You can have a very pretty picture but that does not mean it is a good solution. Unfortunatly, CFD has a very steep initial learning curve. You will be frustrated for a while before you can use CFD tools very effective. Just keep carry on.

 September 21, 2012, 17:32 #6 Member   Ben Join Date: Sep 2012 Posts: 40 Rep Power: 6 I thought that I could jump into it and start off with some basic simulations but you are right, now that I have downloaded the openfoam software it looks very complicated, so many inputs required and I dont even know what 90% of them mean, I will do as you suggested and study the fundamentals and the programming languages before I do any simulations. Thank you for all the help and advice, I will be back as soon as I get stuck

 September 25, 2012, 05:15 #7 Member   Ben Join Date: Sep 2012 Posts: 40 Rep Power: 6 Hello again I am confused, not with the CFD software but with how far it goes, I mean if it is possible to learn CFD without much guidance then why are there PdD courses in CFD at my university? Are CFD jobs hard to find in the UK? Also, if someone did get a job in CFD what would that person be doing , would he be sitting in a office doing simulations all day, would he be writing code, would he be doing maths?

September 25, 2012, 10:43
#8
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Yon Han Chong
Join Date: Jun 2012
Posts: 77
Rep Power: 7
Quote:
 Originally Posted by ben1793 Hello again I am confused, not with the CFD software but with how far it goes, I mean if it is possible to learn CFD without much guidance then why are there PdD courses in CFD at my university?
Those CFD softwares are not answers to everything. There are many situations when we cannot simulate correctly. That could be because the software is not matured enough or you don't have computer resources or simply because you don't understand the fluid physics. Would you let me fly a jumbo jet without a training? In many sense using CFD is even more difficult than flying an airplane. I have done a PhD on CFD but I am still learning after many years in the industry.

Quote:
 Originally Posted by ben1793 Are CFD jobs hard to find in the UK?
I have worked for a major UK engineering company in the past and now I am working for a major US engineering company. Good CFD engineers are hard to come by because even though there are many students who had experiences of running CFD softwares but don't understand the physics (e.g. fluid dynamics, aerothermals). To me learning the software is an easy part. Actually, making judgement calls on assumptions and understanding the result you have is more difficult. Big companies will be willing to bring you over the border to have you if you know what you are doing. That does not mean that you will be paid lots of money but your job security is very high. However, my advice is that if you want to get paid decent money for an engineering job leave UK or go into finance (e.g. actuary, predicting share price is similar to predicting particle movement inside fluid).

Quote:
 Originally Posted by ben1793 Also, if someone did get a job in CFD what would that person be doing , would he be sitting in a office doing simulations all day, would he be writing code, would he be doing maths?
Depends on which company you will join, you could be running CFD to advise on designs, you could be writing code for a software company or staying in academy to work on maths behind CFD softwares. If you are interested in maths, you might want to stay in the academy. Why don't you go on a job search and see where are the demands for the CFD skill?

Last edited by yonchong; September 25, 2012 at 13:26.

 September 25, 2012, 11:48 #9 Member   Ben Join Date: Sep 2012 Posts: 40 Rep Power: 6 Thank you yonchong, you always know the answers to my questions I basically have a load of options since I have almost completed my general engineering course (electrical, mechanical, computer science) at college, I am just confused because of the amount of options available, I could do anything, mechatronics engineering, mechanical engineering with CFD for my PhD, bioengineering or even civil engineering, do you think going into CFD would be a good option? If you could go back and change everything, would you still choose to go for CFD? Is being a CFD engineer repeatable? over my holidays I did a job at a 2D cad design company and hated it because every day it was basically the same thing, just modifying 2D drawings for clients, do you think the same will happen with CFD? Everywhere I look it says CFD and FEA, I thought finite element analysis was stress analysis and was used to find things like the safety factor of a solid model, how does this relate to CFD? Again, just want to say thank you for spending the time to answer my questions, you are really helping me a lot in deciding what I want to do with my future.

September 25, 2012, 14:35
#10
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Yon Han Chong
Join Date: Jun 2012
Posts: 77
Rep Power: 7
Quote:
 Originally Posted by ben1793 I basically have a load of options since I have almost completed my general engineering course (electrical, mechanical, computer science) at college, I am just confused because of the amount of options available, I could do anything, mechatronics engineering, mechanical engineering with CFD for my PhD, bioengineering or even civil engineering, do you think going into CFD would be a good option? If you could go back and change everything, would you still choose to go for CFD?
All of them sounds great but I would not recommend PhD if you have to stay in UK. It would be far more effective if you can find a graduate scheme in a company. You can rotate to different departments and try different things including CFD. That's because in UK the years in the industry counts more than higher degrees in the academy. Also you will get paid better during the same time.

If you think you can move to different countries, PhD will be more useful but, if not, a master degree is still very useful. In fact, I would look at US universities for a master or PhD course because you get much more opportunities here. Pays for research assistants or engineers are better in US and if you go to a US university they do actively try to hold on to you as you are seen as an able person who can contribute to the US economy. (There are big debates about people from India and China going back to their countries to set up rival companies to US.)

If I start over again I would still choose CFD (interesting job, job security etc.) but I would try to go to a US university. It would have been much easier to get a job in US if I did.

Quote:
 Originally Posted by ben1793 Is being a CFD engineer repeatable? over my holidays I did a job at a 2D cad design company and hated it because every day it was basically the same thing, just modifying 2D drawings for clients, do you think the same will happen with CFD?
If you just learn how to run CFD software it would be similar. If you learn the physics (aerodynamics, fluid mechanics, thermals etc) and use CFD as one of your tools to visualise or estimate what you can predict you are in a far better position.

As far as learning CFD software goes, I had a secondary student came in for 2 weeks of work experience. At the end of 2 weeks, she was able to run Fluent and get useful result for us to use. She did not quite understand why she need to do them but she can repeat the runs with some changes when she was told.

However, one would be working 2-3 years as a CFD Engineer before his options will be heard in a regular bases. That's because there are lot more reasons why a CFD result could be wrong than right. That is also why companies are reluctant to hire someone who does not have industrial experiences and difficult to find someone with good experiences.

Quote:
 Originally Posted by ben1793 Everywhere I look it says CFD and FEA, I thought finite element analysis was stress analysis and was used to find things like the safety factor of a solid model, how does this relate to CFD?
There are many situations where fluid and solid interact. It could be the heat transfer between fluid and solid or vibrations between the two. In many case, the hardware will burn or break because of these interaction. An example would be turbine blades in gas turbine engine, too hot or fluid excite the blade it will fail catastrophically. Say the turbine blade will melt at 2000K. You want to designed the system at 1800K so you have some safty factor in the hardware. Normally you will run CFD and pass the result to FEA to use in its calculation or vice verse. You can even do a conjugate heat transfer calculation. Together you would estimate the life of the component with engineering judegments.

Quote:
 Originally Posted by ben1793 Again, just want to say thank you for spending the time to answer my questions, you are really helping me a lot in deciding what I want to do with my future.
I hope that this is somewhat useful to you.

 September 26, 2012, 13:09 #12 Member   Ben Join Date: Sep 2012 Posts: 40 Rep Power: 6 Thank you yonchong and ABF for spending the time and effort to answer my question and help me decide what I want to do with my future. Last edited by ben1793; October 5, 2012 at 14:27.

 September 28, 2012, 06:10 #13 New Member   AS Join Date: Jul 2009 Posts: 16 Rep Power: 10 If you do attempt any CFD pre-uni, one issue you will face is that open source CFD codes are generally very hard to use (at least for OpenFOAM and code_STAURNE, I can't comment on others). Commercial codes are easier, but extremely expensive. There is basically a barrier to entry before uni. At uni, the uni will have licenses for FLUENT or starCCM+ or something fairly user friendly-so you can learn how to use a commercial code before taking the open source plunge. If your aims are simply to learn CFD, then start with just the FD bit pre-uni, and you will be in an excellent position to excel at CFD when the time comes. Believe me, there is plenty of fluid dynamics theory to keep you going for many years!! As for C++ / fortran, etc., it is not necessary for using CFD codes (even open source ones). It's necessary for developing a code obviously (something you won't do until PhD level or if you get a development job with ANSYS or CD-adapco etc.). That said, programming knowledge will be invaluable for other areas of a mechanical engineering degree.

 September 28, 2012, 17:22 #14 Member   Ben Join Date: Sep 2012 Posts: 40 Rep Power: 6 Thanks for the info Last edited by ben1793; October 1, 2012 at 02:46.

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