compressible low-Re turbulence model

immortality · May 17, 2013, 03:05

what low-Re models are available for compressible flows?
I know there isn't any for kOmegaSST,but what are probable replacements(for other models)?

jola · May 17, 2013, 03:51

Most low-Re models can be used also for compressible flows, assuming they are formulated in a correct way. Only hypesonic flow with very strong compressibility effects require special compressible turbulence models. You can find equation details here: http://www.cfd-online.com/Wiki/Favre...okes_equations

immortality · May 17, 2013, 10:14

Thank you Mr.Larrson.
I noticed befor that for example there is not any low-Re kOmegaSST model for compressible flows in OF
http://www.openfoam.org/mantisbt/vie..._page.php?id=6
which low-Re model you suggest to me?how can I find the appropriate coefficients,is there an example tutorial?
thanks.

ignacio · May 17, 2013, 10:51

Hello Ehsan,

chtMultiRegionFoam uses Low Reynolds models for compressible flows.
I am using kOmega SST-LowRe with it now
=)

immortality · May 17, 2013, 11:51

Hi Ignacio.
thanks for your replying.
where turbulent models are there in the folder of chtMultiRegionFoam?
then why Dr.Weller told me that they have not a sponsor for kOmegaSST low-Re models?
could you guide me more specific to find the model and related coefficients?
thanks.

immortality · June 5, 2013, 23:55

hi
@Ignatio:
Dear Ignacio
Could you please tell me more how to perform a low-Re turbulent study in a compressible unsteady case?
There are some folders in the solver you mentioned.
And what about other settings and mesh requisits to have a low-Re study?
Could you send me your case please?
@Jola:
Dear Jola could you introduce me some of methods that are appropriate for compressible to be more certained?
is kklOmegaSST suitable(for more sure)?
(Dr.Weller told me its an incompressible method)
How can i find out incompressible models are also applicable for compressible cases from the formulas?
What other methods exist?
Thanks

pete · June 6, 2013, 04:57

Just make sure that when impementing the turbulence model the incompressibility condition of zero divergence of the velocity field has not been used. In compressible flows this assumption is not correct and you can not use it in for example the Boussinesq eddy viscosity assumption. CFD-Wiki has more info, look for example here:

http://www.cfd-online.com/Wiki/Bouss...ity_assumption

immortality · June 10, 2013, 10:09

Hi
I'm using low-Re kOmegaSST but time step is too low(about 5e-10) due to small cell near the wall I assume.how can improve it for having more quick run?

immortality · June 11, 2013, 05:58

Hi again
since rhoCentralFoam is explicit I changed to sonicFoam.
also now I use LaunderSharmaKE.
now run is rapid enough.but a problem is seen in the first top cell in opening.its pressure goes too high.I think because velocity is near zero in the first cell center(in laminar-sublayer) and since I have set a totalPressure in opening the pressure in the cell near the wall goes high.am I right?!
or its only because of mesh in flow-direction that is much bigger than normal to wall direction?
I'll attach a figure soon/.

May 17, 2013, 03:05	compressible low-Re turbulence model	#1
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 27	what low-Re models are available for compressible flows? I know there isn't any for kOmegaSST,but what are probable replacements(for other models)? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

May 17, 2013, 10:14		#3
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 27	Thank you Mr.Larrson. I noticed befor that for example there is not any low-Re kOmegaSST model for compressible flows in OF http://www.openfoam.org/mantisbt/vie..._page.php?id=6 which low-Re model you suggest to me?how can I find the appropriate coefficients,is there an example tutorial? thanks. __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

May 17, 2013, 10:51		#4
ignacio Member Ignacio Join Date: Jan 2013 Posts: 33 Rep Power: 13	Hello Ehsan, chtMultiRegionFoam uses Low Reynolds models for compressible flows. I am using kOmega SST-LowRe with it now =) immortality likes this.

May 17, 2013, 11:51		#5
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 27	Hi Ignacio. thanks for your replying. where turbulent models are there in the folder of chtMultiRegionFoam? then why Dr.Weller told me that they have not a sponsor for kOmegaSST low-Re models? could you guide me more specific to find the model and related coefficients? thanks. __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

June 5, 2013, 23:55	kkLOmegaSST	#6
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 27	hi @Ignatio: Dear Ignacio Could you please tell me more how to perform a low-Re turbulent study in a compressible unsteady case? There are some folders in the solver you mentioned. And what about other settings and mesh requisits to have a low-Re study? Could you send me your case please? @Jola: Dear Jola could you introduce me some of methods that are appropriate for compressible to be more certained? is kklOmegaSST suitable(for more sure)? (Dr.Weller told me its an incompressible method) How can i find out incompressible models are also applicable for compressible cases from the formulas? What other methods exist? Thanks __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

May 17, 2013, 03:51		#2
jola Administrator Jonas Larsson Join Date: Jan 2009 Location: Gothenburg, Sweden Posts: 835 Rep Power: 10	Most low-Re models can be used also for compressible flows, assuming they are formulated in a correct way. Only hypesonic flow with very strong compressibility effects require special compressible turbulence models. You can find equation details here: http://www.cfd-online.com/Wiki/Favre...okes_equations

June 6, 2013, 04:57		#7
pete Administrator Peter Jones Join Date: Jan 2009 Posts: 682 Rep Power: 10	Just make sure that when impementing the turbulence model the incompressibility condition of zero divergence of the velocity field has not been used. In compressible flows this assumption is not correct and you can not use it in for example the Boussinesq eddy viscosity assumption. CFD-Wiki has more info, look for example here: http://www.cfd-online.com/Wiki/Bouss...ity_assumption immortality likes this.

June 10, 2013, 10:09		#8
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 27	Hi I'm using low-Re kOmegaSST but time step is too low(about 5e-10) due to small cell near the wall I assume.how can improve it for having more quick run? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

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