
[Sponsors] 
May 11, 2007, 06:13 
Hi all,
comparing the RANSso

#1 
Member
Rolando Maier
Join Date: Mar 2009
Posts: 89
Rep Power: 9 
Hi all,
comparing the RANSsolver turbFoam and the LESsolver oodles there is one eye catching difference. In the LES solver the sgs model is calculated at the beginning of a time step and in the RANS solver the turbulence model is calculated at the end of it. Does it make a difference at all where I place the turbulence/sgs model? What happens with moving meshes, when a phi correction is done at the beginning of a time step? Rolando 

June 1, 2007, 07:52 
Hi,
I want to write a hybrid

#2 
Member
Rolando Maier
Join Date: Mar 2009
Posts: 89
Rep Power: 9 
Hi,
I want to write a hybrid solver, which can be used both for RANS and LES calculations. Comparing the two basic solvers of that type, "oodles" and "turbFoam", I noticed, that in "oodles" the turbulence equations are solved at the begin of the timestep, whereas in "turbFoam" the equations are solved at the end of the timestep. Does it make any difference where the turbulence equations are solved? Rolando 

June 1, 2007, 12:15 
No, not really. But why would

#3 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 13 
No, not really. But why would you want to write a new solver? The only real difference between oodles and turbFoam is the turbulence models. In fact the SpalartAllmaras and oneEqEddy LES models are DES models which blend between LES and RANS modeling based on wall distance.


June 1, 2007, 12:24 
Hello Eugene,
thatīs what I w

#4 
Member
Rolando Maier
Join Date: Mar 2009
Posts: 89
Rep Power: 9 
Hello Eugene,
thatīs what I want to do. I want to do DES calculations. Further I want to do some calculations with the models in RANS mode. There are also some small additional features I integrated in my solver. Having a single hybrid solver would ease the maintenance of the it. Can you tell me, why it is a difference to calculate the equations at the beginning or the end of the loop? Is the placement at the beginning all right for DES calculations? Rolando 

June 1, 2007, 12:37 
The only difference between pl

#5 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 13 
The only difference between placing it at the beginning or end of the loop is during the first timestep.
The question is simply, what do you think is better: calculating the flow first with rubbish turbulence, or calculating the turbulence first with rubbish flow field. Since everything is pretty rubbish at first I doubt it will make a significant difference. I would use the oodles solver as my base simply because it is more advanced (uses the SIMPISO algorithm). This algorithm will probably be applied to turbFoam in due course. 

June 1, 2007, 12:55 
Then it should be possible to

#6 
Member
Rolando Maier
Join Date: Mar 2009
Posts: 89
Rep Power: 9 
Then it should be possible to do RANS calculations with the oodles solver, right?
What do you mean with SIMPISO algorithm? In the oodles solver there is the same PISO algorithm as in turbFoam. Rolando 

June 1, 2007, 14:10 
Yes, I dont see why not, as lo

#7 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 13 
Yes, I dont see why not, as long as you use a "RANS" LES model.
oodles has a SIMPISO/PIMPLE solver, dont let the PISO entry in the fvSolution fool you. It only does full convergence on the final corrector step and is about twice as fast as PISO as a result. 

June 1, 2007, 15:39 
Thanks a lot Eugene,
I think

#8 
Member
Rolando Maier
Join Date: Mar 2009
Posts: 89
Rep Power: 9 
Thanks a lot Eugene,
I think with "RANS" LES model you mean, that the RANS model is derived from "LESmodel" and not from "turbulenceModel", right? Rolando 

June 4, 2007, 05:37 
That would be one way yes.

#9 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 13 
That would be one way yes.


June 4, 2007, 05:42 
Thanks a lot Eugene.

#10 
Member
Rolando Maier
Join Date: Mar 2009
Posts: 89
Rep Power: 9 
Thanks a lot Eugene.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Coefficienct in the oodles  loneboard  OpenFOAM Running, Solving & CFD  4  March 12, 2009 22:18 
Oodles and more  r2d2  OpenFOAM Running, Solving & CFD  10  September 23, 2007 01:54 
Parallel oodles  sriharsha  OpenFOAM Running, Solving & CFD  8  January 3, 2007 12:29 
Parallel oodles  sriharsha  OpenFOAM Running, Solving & CFD  0  December 27, 2006 18:25 
Parallel oodles  sriharsha  OpenFOAM Running, Solving & CFD  0  December 27, 2006 18:21 