Turbulence

hashem_1064 · October 11, 2009, 09:01

hi all
I want to model a boat using CFX. The Re is about 39e+06. what turbulence option is the most suitable for this modeling? if k-epsion, how do I should choose constants k and epsilon for?

thanks alot

ghorrocks · October 11, 2009, 17:40

The answer depends on what you want to do in the analysis. If you want detailed boundary layer and/or turbulence transition data then you must use SST, possibly with the turbulence transition model. If you just want a lift/drag number then a standard wall function approach should be fine then I would recommend SST.

So my first guess for your application would be SST as it is a good general purpose turbulence model. Don't fiddle with any of the constants unless you REALLY know what you are doing.

hashem_1064 · October 12, 2009, 01:36

thank you Glenn
my aim is to calculate value of lift and drag. so according to your suggestion SST would be the best case. but my question is still "How should I assign" appropriate value to the constants? Is there any guideline to have an accurate numbers for those?

thank
Hashem

ghorrocks · October 12, 2009, 06:10

SST is a good general purpose turbulence model which you should use unless have a good reason not to.

As I said, don't fiddle with the model constants. The defaults are good for most applications.

October 11, 2009, 09:01	Turbulence	#1
hashem_1064 New Member hashem Join Date: May 2009 Posts: 17 Rep Power: 16	hi all I want to model a boat using CFX. The Re is about 39e+06. what turbulence option is the most suitable for this modeling? if k-epsion, how do I should choose constants k and epsilon for? thanks alot

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October 11, 2009, 17:40		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,690 Rep Power: 143	The answer depends on what you want to do in the analysis. If you want detailed boundary layer and/or turbulence transition data then you must use SST, possibly with the turbulence transition model. If you just want a lift/drag number then a standard wall function approach should be fine then I would recommend SST. So my first guess for your application would be SST as it is a good general purpose turbulence model. Don't fiddle with any of the constants unless you REALLY know what you are doing.

October 12, 2009, 01:36		#3
hashem_1064 New Member hashem Join Date: May 2009 Posts: 17 Rep Power: 16	thank you Glenn my aim is to calculate value of lift and drag. so according to your suggestion SST would be the best case. but my question is still "How should I assign" appropriate value to the constants? Is there any guideline to have an accurate numbers for those? thank Hashem

October 12, 2009, 06:10		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,690 Rep Power: 143	SST is a good general purpose turbulence model which you should use unless have a good reason not to. As I said, don't fiddle with the model constants. The defaults are good for most applications.