# Computational & Run Time requirements for CAA

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 June 16, 2010, 01:36 Computational & Run Time requirements for CAA #1 New Member   Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 9 Hi, I'm a undergraduate student and I'm about to start a CAA research in CFX. I've no previous experience in this area, so in order to write my project I need to know the computational and run time requirements for a simple geometry. How many nodes would I need for a LES method? Please, any comment will be welcome. Thanks

 June 16, 2010, 08:22 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 It depends on what you are modelling, of course. But any LES model will involve large meshes and long run times. LES is very computationally expensive.

 June 16, 2010, 10:16 #3 New Member   Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 9 Thank you Glenn Horrocks for your answer. My first idea is to model an airfoil-slat geometry, but I thing I won't have enough computational resource to explore this problem in CFX, mainly because its iterative solver. Maybe a CAA designed software should allow me to do this. So in order to write my project I need to know what kind of geometry I will be able to explore in CFX. Thanks

 June 16, 2010, 10:21 #4 Senior Member   Join Date: Jan 2010 Posts: 110 Rep Power: 8 Basically in a LES simulation you try to represent directly the large scales and the effects of the small scales are modelled. The required grid spacing h is proportional to a specified filter width that should be smaller than the size of the smallest energy-containing motions. you can see an overview of all modeling approaches in Pope for example. Regards

June 16, 2010, 18:38
#5
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Glenn Horrocks
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Quote:
 My first idea is to model an airfoil-slat geometry
What Re and Ma numbers?

 June 17, 2010, 18:07 #6 New Member   Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 9 Re~9e6 e Ma=0.3

 June 17, 2010, 19:40 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 This is quite a high Re number, meaning that the turbulent structures will be quite small. On top of that you will have compressibility effects with Ma=0.3. This is definitely going to be a challenging model and will require a compute cluster of some size and lots of run time.

 June 21, 2010, 19:01 #8 New Member   Danillo Cafaldo dos Reis Join Date: Jun 2009 Posts: 12 Rep Power: 9 Thank you Glenn Horrocks and Antonio for your answers. I will change my initial idea and simulate a Mixing Layer, that can be interpreted as a very simplified model of slat. I'm sure that this will be possible to do. Best regards

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