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CFX best practice for external flows

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Old   July 31, 2008, 04:13
Default CFX best practice for external flows
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siw
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Hi,

Does any know of some best practice guides for external flow (flow over aircraft, 2-D aerofoils and external stores) using CFX?

For most of my work I conduct grid independence tests , but I find runs become independent with millions of elements.

But was gauging such issues as fluid domian size, I have a good idea what is best for me, but would be interested in what others use. The same goes for inflation layer details - I've not really got a full sense on using yplus and stick with first-layer thinkness instead. And anything else I missed.

Thanks.
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Old   August 3, 2008, 18:46
Default Re: CFX best practice for external flows
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Glenn Horrocks
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Hi,

That's right - external aircraft aerodynamics will require millions of elements. If you are adding external stores then more like tens or hundreds of millions. That's CFD for you, if you want accurate results for this type of modelling you must get a computer capable of running simulations of this magnitude.

Glenn Horrocks
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Old   August 3, 2008, 20:17
Default Re: CFX best practice for external flows
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Rogerio Fernandes Brito
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Use Hexa mesh, then you will have less computational effort and less time of cpu.
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Old   August 4, 2008, 02:32
Default Re: CFX best practice for external flows
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siw
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Glenn, I'm running with very large element amounts. Odd how in many academic papers runs are made with less than 1 million, however they always omit the details.

With all the options in CFX, of which I don't use many as I don't have the necessary numbers, is there a guide as to what are best for external flow?

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Old   August 4, 2008, 21:58
Default Re: CFX best practice for external flows
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Glenn Horrocks
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Hi,

External aerodynamics with less than 1M elements is either inviscid or viscous and hopelessly inaccurate.

As to what options to choose - that depends on what you want to do. They would not pay my salary if there was a simple answer to that question.

Glenn Horrocks
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Old   May 3, 2009, 22:44
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Shawn Givler
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siw

For bluff bodies and streamlined vehicle aerodynamics my rules of thumb are 2 vehicle widths to each side, 6-10 vehicle lengths downstream, and 2-4 vehicle lengths upstream.

Shawn
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