turbulent kinetic energy in TGV case

baraban55 · March 11, 2012, 07:57

Hello!
I try to use Two-equation

-

eddy viscosity model for Taylor-Green Vortex case with Re=3000. I use physical space code with weno3 scheme. I don't want to transport neither turbulent kinetic energy nor turbulent dissipation so I looking for an appropriate models. Kindly ask you to help me.

cfdnewbie · March 11, 2012, 11:35

I'm not sure what you are trying to do and what you are asking for....so you are doing an LES, and you are looking for a SGS model? Is that it? I don't understand your comment about using the k eps model without using the appropriate transport equations.... ???

baraban55 · March 11, 2012, 13:23

Quote:

Originally Posted by cfdnewbie

I'm not sure what you are trying to do and what you are asking for....so you are doing an LES, and you are looking for a SGS model? Is that it? I don't understand your comment about using the k eps model without using the appropriate transport equations.... ???

Thank you for your reply. Actually I'm trying to do RANS. I use this model: http://www.cfd-online.com/Wiki/Linea...scosity_models. For eddy viscosity I use the same model as in k-epsilone model with C=0.09. So I'm wondering if it is possible not to transport k and epsilone but model them in case of TGV? What models for k and epsilone can be implement in that case? I would really apreciate any help.

baraban55 · March 11, 2012, 13:35

Quote:

Originally Posted by cfdnewbie

I'm not sure what you are trying to do and what you are asking for....so you are doing an LES, and you are looking for a SGS model? Is that it? I don't understand your comment about using the k eps model without using the appropriate transport equations.... ???

Thank you for your reply. Actually I'm trying to do RANS. I use this model: http://www.cfd-online.com/Wiki/Linea...scosity_models. For eddy viscosity I use the same model as in k-epsilone model with C=0.09. So I'm wondering if it is possible not to transport k and epsilone but model them in case of TGV? What models for k and epsilone can be implement in that case? I would really apreciate any help.

cfdnewbie · March 11, 2012, 13:59

Dear baraban,
I'm not sure if a RANS approach will get you anywhere with this problem. The TGV is highly unsteady and strongly governed by vortex interaction, so a RANS approach (which does not resolve any eddies) will not give you a good approximation. if you just want to check that, then RANS is fine, but for much else, LES will be needed!

baraban55 · March 11, 2012, 15:03

Quote:

Originally Posted by cfdnewbie

Dear baraban,
I'm not sure if a RANS approach will get you anywhere with this problem. The TGV is highly unsteady and strongly governed by vortex interaction, so a RANS approach (which does not resolve any eddies) will not give you a good approximation. if you just want to check that, then RANS is fine, but for much else, LES will be needed!

But in my case I don't need a good aproximation. I just want to find rough model for turbulent kinetic energy and turbulent dissipation for TGV. May be than I'll compare the results I'll get with 2 transport equations and models for k and epsilon.
I can also get some DNS results for evalution of turbulent kinetic energy and put it to the k-epsilone model. Than I'll get the limit of prediction for that model for TGV case so I can compare the results of rough models for turbulent kinetic energy with that limit.
I tried to find some models on google and on wos but failed. I also checked it in "Turbulent Flows" by Pope and didn't find the answer. May be you can suggest some other source of searching? I would really appreciate any help).

sbaffini · March 12, 2012, 16:12

As previously stated by cfdnewbie, the Taylor-Green vortex case is usually studied to check model capabilities in predicting transition to turbulence in a setting which does not involve boundary conditions or walls. As long as i understand the Taylor-Green vortex case and the URANS turbulence models you wont get any help from any source as it has never been done with URANS. The reason is that it is really out of the modeling capabilities of the URANS approach so no one tryied to get an answer which could never be useful in practice. Nonetheless, you can clearly do the job in any case; just take any available reference on TGV and do the same simulation with your model of choice.

The first reference which comes in my mind is by Fauconnier et al., some work of Drikakis et al., Hickel and maybe someone at Stanford (try to look in the CTR material from the last 5-6 years)

Also, the initialization of this flow is very easy (compared to HIT) so its everything really straight... except that you have to somehow set your initial condition for the URANS turbulence model. This is going to be awkward...

March 11, 2012, 07:57	turbulent kinetic energy in TGV case	#1
baraban55 New Member Join Date: Mar 2012 Posts: 4 Rep Power: 14	Hello! I try to use Two-equation - eddy viscosity model for Taylor-Green Vortex case with Re=3000. I use physical space code with weno3 scheme. I don't want to transport neither turbulent kinetic energy nor turbulent dissipation so I looking for an appropriate models. Kindly ask you to help me.

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March 11, 2012, 11:35		#2
cfdnewbie Senior Member cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 20	I'm not sure what you are trying to do and what you are asking for....so you are doing an LES, and you are looking for a SGS model? Is that it? I don't understand your comment about using the k eps model without using the appropriate transport equations.... ???

March 11, 2012, 13:59		#5
cfdnewbie Senior Member cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 20	Dear baraban, I'm not sure if a RANS approach will get you anywhere with this problem. The TGV is highly unsteady and strongly governed by vortex interaction, so a RANS approach (which does not resolve any eddies) will not give you a good approximation. if you just want to check that, then RANS is fine, but for much else, LES will be needed!

March 12, 2012, 16:12		#7
sbaffini Senior Member Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,152 Blog Entries: 29 Rep Power: 39	As previously stated by cfdnewbie, the Taylor-Green vortex case is usually studied to check model capabilities in predicting transition to turbulence in a setting which does not involve boundary conditions or walls. As long as i understand the Taylor-Green vortex case and the URANS turbulence models you wont get any help from any source as it has never been done with URANS. The reason is that it is really out of the modeling capabilities of the URANS approach so no one tryied to get an answer which could never be useful in practice. Nonetheless, you can clearly do the job in any case; just take any available reference on TGV and do the same simulation with your model of choice. The first reference which comes in my mind is by Fauconnier et al., some work of Drikakis et al., Hickel and maybe someone at Stanford (try to look in the CTR material from the last 5-6 years) Also, the initialization of this flow is very easy (compared to HIT) so its everything really straight... except that you have to somehow set your initial condition for the URANS turbulence model. This is going to be awkward...