# 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: 16 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: 17,729 Rep Power: 143 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: 16 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: 16 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
Super Moderator

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: 16 Re~9e6 e Ma=0.3

 June 17, 2010, 19:40 #7 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,729 Rep Power: 143 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: 16 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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