Basic explanation of turbulence models

Ashh · October 10, 2013, 01:01

I've been searching for a while for a low-level description of how the turbulence models work and am not finding very much. So far I have:

K-e:
Uses turbulence energy (K) and it's rate of dissipation (e). Good standard model that works in most industrially relevant cases.
Not good with:
- flow reattachment
- flow seperation
- flow recovery

SST:
Uses K-e in free flow and K-w (w is the frequency of eddie currents) which is better for wall boundary layers.
- bad with flow recovery after flow reattachment

BSL:
Baseline Reynolds Model? Can be used with a rougher mesh?

SSG:
Speziale-Sarkar-Gatski. Better than BSL for high Reynolds numbers?

As you can see I have pretty much no information on BSL and SSG. Any information will be greatly appreciated!

Cheers
Ash

pz21 · October 10, 2013, 03:29

Dear Ash,
I suggest that the help documentation of any CFD code may help you. For example, the section of "Turbulence Models" in CFX Modeling Guide offers a basic capability description of various turbulence models. And the Theory Guide tells how these turbulence models work.
Sorry for no detailed information to help you.

ghorrocks · October 10, 2013, 06:12

The turbulence modelling textbook "turbulence Modelling for CFD" by Wilcox is a excellent textbook in this area.

To correct some of your points:
- k-e, has known problems at stagnation points, separations (both detactment and reattachment) but pretty good for bulk flows. Very poor at rotating flows and anisotropic turbulence.
- SST - better at all these conditions, has models available which might help for rotating flows and turbulence transition and a few other special cases. This should be your default selection for a turbulence model unless you have a very good reason to choose something else.
- All the Reynolds stress models - can capture flow rotation and anisotropic turbulence, but rarely end up being much more accurate than a reasonable 2-eqn model anyway due to the large number of assumptions required to get them to work. Also devilishly hard to converge.
- And then there is DES, SAS, LES, DNS - these are advanced models which you should only consider when you have a good knowledge of turbulence models. Using them without knowing what they do is a receipe for disaster.

October 10, 2013, 01:01	Basic explanation of turbulence models	#1
Ashh New Member Ash Join Date: Oct 2013 Posts: 3 Rep Power: 13	I've been searching for a while for a low-level description of how the turbulence models work and am not finding very much. So far I have: K-e: Uses turbulence energy (K) and it's rate of dissipation (e). Good standard model that works in most industrially relevant cases. Not good with: - flow reattachment - flow seperation - flow recovery SST: Uses K-e in free flow and K-w (w is the frequency of eddie currents) which is better for wall boundary layers. - bad with flow recovery after flow reattachment BSL: Baseline Reynolds Model? Can be used with a rougher mesh? SSG: Speziale-Sarkar-Gatski. Better than BSL for high Reynolds numbers? As you can see I have pretty much no information on BSL and SSG. Any information will be greatly appreciated! Cheers Ash

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October 10, 2013, 03:29		#2
pz21 New Member Join Date: Nov 2010 Posts: 5 Rep Power: 16	Dear Ash, I suggest that the help documentation of any CFD code may help you. For example, the section of "Turbulence Models" in CFX Modeling Guide offers a basic capability description of various turbulence models. And the Theory Guide tells how these turbulence models work. Sorry for no detailed information to help you.

October 10, 2013, 06:12		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	The turbulence modelling textbook "turbulence Modelling for CFD" by Wilcox is a excellent textbook in this area. To correct some of your points: - k-e, has known problems at stagnation points, separations (both detactment and reattachment) but pretty good for bulk flows. Very poor at rotating flows and anisotropic turbulence. - SST - better at all these conditions, has models available which might help for rotating flows and turbulence transition and a few other special cases. This should be your default selection for a turbulence model unless you have a very good reason to choose something else. - All the Reynolds stress models - can capture flow rotation and anisotropic turbulence, but rarely end up being much more accurate than a reasonable 2-eqn model anyway due to the large number of assumptions required to get them to work. Also devilishly hard to converge. - And then there is DES, SAS, LES, DNS - these are advanced models which you should only consider when you have a good knowledge of turbulence models. Using them without knowing what they do is a receipe for disaster.