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RobinCris January 16, 2012 06:04

How do I start
 
Hello there

I never used CFD before.

My client want to build a complex of 2 high raise buildings (100m) in an area of 3 floor buildings.

Before he can do so, I need to check the winds.
I need to understand and write a detail report about the influence of those two building on the level 0 surrounding environment.


What are my options?
How complicated this model is?
I am a very techno-logic person.

basically .... How do I start?

Thank you for sending me to the right direction and for any information.

truffaldino January 16, 2012 10:15

I think the easiest way to go is to use flow modelling with FLUENT. If you have newer used such a sofware before it could take some time to learn.

As an example you can take a look at this paper

http://www.iaeng.org/publication/WCE...p1601-1605.pdf

Truffaldino

cfdnewbie January 16, 2012 10:56

If you have no previous experience in fluid dynamics, I'd recommend getting started with books about basic theory.

http://www.amazon.co.uk/Fundamentals...tt_at_ep_dpt_1

While I think it is not the best book, it is pretty well written and easy to understand. I think it will be mandatory to understand (incompressible) fluid motion before you try to model your wind problem!

hope this helped!
cheers

sail January 16, 2012 11:27

Hi Robin. CFD is an interesting topic, but also a very complex one. It might take some time to produce meaningful results.

First of all you should be confident with the physic and the numerics behind those colorful images: i might reccomand a couple of books, among many: http://www.cfd-online.com/Books/show_book.php?book_id=37

and

http://www.cfd-online.com/Books/show_book.php?book_id=3

both should give you a basic understanding of what CFD is and how does it works.

then there is the pratical side: get a cfd software and use it. you might choose a commercial version (fluent, cfx, star ccm+) or a opensource one (OpenFOAM).

Commercial software helps to make the learning courve less steep by providing the user with a GUI and a very well written documentation and tutorials. on the other hand they are quite expensive and you need to do quite some work with them to be able to repay the initial investment.

After you get past the tutorial phase, with both commercial or Opensource Sw, remember to compare your results with experiamental results obtained in the literature, or at least with empirical formulations: for example the british standard (don't remember the number, i might check if you need them) provide some empirical formulations to estimate the pressure on the bulding surfaces depending on the position, surrondings, wind history, geometry etc.

I find the BS approach to be a useful reality check.

a third option could be to give this work to a CFD Consulting company. For a Full disclosure, I must say that I own one of such companies, so take my words with a ton of salt. :D

Martin Hegedus January 16, 2012 17:25

Here's my two cents. If you are not familiar with CFD and fluid dynamics, you have a steep learning curve ahead of you and you are taking a risk that you'll get the wrong answer. In fact, I will guarantee, more or less, that your first results will be incorrect. Read some of threads and if you feel that the subject, along with the concept or Reynolds number and boundary layers, is outside of your scope of knowledge, seek someone who is knowledgeable. Maybe talk to a professor at a local university. If someone is paying you for the results, you are responsible for them.

Edit: It sounds like you have two scales going on, big building, small buildings. It is going to be easy to get an incorrect answers. And, you may not have the computational resources to do a full analysis so you may need to simplify your answer and provide errors bands. That takes a lot of experience.

cfdnewbie January 16, 2012 18:03

Good thoughts, Martin. This is not meant as an insult of the guy asking for help, but sometimes, when reading the questions people pose here, I get the feeling that often people are doing (or are forced to do) CFD that have little or no experience with it and just push the buttons on their black box aka commercial solver.
There's nothing wrong with playing around and learning by doing, I just get the feeling that many companies force their employees into this field without giving them a proper education in CFD...

Martin Hegedus January 16, 2012 19:29

Quote:

Originally Posted by cfdnewbie (Post 339611)
Good thoughts, Martin. This is not meant as an insult of the guy asking for help, but sometimes, when reading the questions people pose here, I get the feeling that often people are doing (or are forced to do) CFD that have little or no experience with it and just push the buttons on their black box aka commercial solver.
There's nothing wrong with playing around and learning by doing, I just get the feeling that many companies force their employees into this field without giving them a proper education in CFD...

Oh, definitely not an insult to the original poster. Unfortunately engineers who use CFD are told how easy it is to do or what can be done by commercial companies and researches. For obvious reasons. But, in the end we are trying to model semi-chaos. Chaos with an underlying, somewhat simple, set of equations. Fluid dynamics results can be extremely nonlinear.

cfdnewbie January 17, 2012 12:16

Quote:

Originally Posted by Martin Hegedus (Post 339619)
Oh, definitely not an insult to the original poster. Unfortunately engineers who use CFD are told how easy it is to do or what can be done by commercial companies and researches. For obvious reasons. But, in the end we are trying to model semi-chaos. Chaos with an underlying, somewhat simple, set of equations. Fluid dynamics results can be extremely nonlinear.

I agree. We sometimes have people from the industry come to us and ask for help with a simulation, because they can't figure out what went wrong or why their results are so far off from their experiments. Some of these folks are very well educated, but sad to say that most of them (calling themselves "CFD experts") sadly lack even basic understanding of mathematics and physics. It is by no means their fault, but the companies who hire young engineers and teach them how to use their commercial solver of choice - but most of the time, they forget to teach numerical mathematics.

I would encourage everybody who uses these codes and feels that he has no real understanding of what is going on to take a couple of evenings and write his own 2D, structured solver of choice. FD, FV, whatever feels more comfortable.

There are many numerics lectures out there in the www, or on itunes, so people can get a solid education in CFD, if their employer is not able to give them one.


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