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-   -   tried with pimpleFoam and a big CFL = 5 (http://www.cfd-online.com/Forums/openfoam-solving/70743-tried-pimplefoam-big-cfl-5-a.html)

 ivan_cozza December 4, 2009 05:40

tried with pimpleFoam and a big CFL = 5

Hi Foamers,
has anyone some experience in using the pimpleFoam solver?
I'm trying to apply it on a low Mach, high Re airfoil in a jet flow.
The airfoil has a separation bubble just after the leading edge as it has a big camber, so simpleFoam is not able to obtain a stable bubble. I tried with pimpleFoam and a big CFL = 5, using standard setups for fvSchemes and fvSolution (like in the tutorial), but I can't obtain anything meaningful.
So, before starting to play with schemes and solver, is this solver suitable for this external aerodynamics problems?
Thanks a lot!
Ivan

 ata December 5, 2009 07:37

pimpleFoam

Hi Ivan
As you know pimpleFoam is for:
Large time-step transient solver for incompressible, flow using the PIMPLE (merged PISO-SIMPLE) algorithm.Turbulence modelling is generic, i.e. laminar, RAS or LES may be selected.
So I think you select right solver and problem is from other point.
Best regards

Ata

 ivan_cozza December 6, 2009 07:56

Quote:
 Originally Posted by ata (Post 238813) Hi Ivan As you know pimpleFoam is for: Large time-step transient solver for incompressible, flow using the PIMPLE (merged PISO-SIMPLE) algorithm.Turbulence modelling is generic, i.e. laminar, RAS or LES may be selected. So I think you select right solver and problem is from other point. Best regards Ata
Thank you Ata for the help, but the meaning of my post was to have a bit more informations than reading the User guide (that I did by myself). What users may need is sharing the informations of experienced users of this solver, in order to put in evidence capabilities and shortcomings of it.
Ivan

 alberto December 7, 2009 03:44

Hi Ivan,

can you post a contour or some info about what you obtain with the pimpleFoam in your case? What are average Ma and Re?

pimpleFoam is basically pisoFoam with substep iterations in order to achieve convergence with larger time steps/Courant numbers, allowing variable under-relaxation. In other words, if pisoFoam (unsteady incompressible solver) is suitable for your case, pimpleFoam is as well.

Quote:
 Originally Posted by ivan_cozza (Post 238862) What users may need is sharing the informations of experienced users of this solver, in order to put in evidence capabilities and shortcomings of it.
Hehe, I think I know the feeling :D

Best,

 ata December 7, 2009 05:17

pimpleFoam help

Hi Ivan
You told (like in the tutorial). Absolutely when I sow that you are a senior member I write "As you know". However The problem was thatyou do not explain enough. In example how residuals behave? Is it converges? How much is CFL? What kind of B.C.s you use? Do you use nNonarthogonalCorrection? What number?
And alberto you are a very smart. I think Ivan gives you a response as sent for me.
Best regards

Ata

 ivan_cozza December 7, 2009 09:40

Quote:
 Originally Posted by alberto (Post 238916) Hi Ivan, can you post a contour or some info about what you obtain with the pimpleFoam in your case? What are average Ma and Re? pimpleFoam is basically pisoFoam with substep iterations in order to achieve convergence with larger time steps/Courant numbers, allowing variable under-relaxation. In other words, if pisoFoam (unsteady incompressible solver) is suitable for your case, pimpleFoam is as well.
Hi Alberto!
I'm sorry not to post any contour of my test case, on wednesday when I'm back at the office I will do it.

My test case parameters are: 2D asymmetric airfoil Mach about 0.1, Re about 5x10^5, AOA = 0° (so the stagnation point is on the suction side, there is a separation on the pressure side identified by both experiments and other softwares calculations).

I choose a SST k-omega RANS model, with low Re treatment of the walls (I've implemented the Menter's B.C. for omega, valid for y+ less than 3, k fixedValue 1e-10, my y+ is less than 2 everywhere).

With pisoFoam I obtained a good result with Max CFL about 2 (gamma schemes and backward scheme for time), converged everywhere excepting for the separation bubble, where I have a small release of unsteady structures (so the bubble is not stable).

Other partners involved in the same calculations, told me that they obtained a stable bubble using a large CFL value, and I repeated the same calculation with StarCCM+ with a very large CFL (more than 20) and I obtained I stable bubble (but with very bad CP on the airfoil, so OF did it better :D).

I decided to try with pimpleFoam in order to use a very high CFL as well, but for CFL higerh than 5 everything blows up, and even for CFL of the order of 5 the results are completely crazy.

This is the story so far, on wednesday the images!

@ATA
I have to apologize with you if my answer sounded like a firing on you, I just want to say that my question was not on a theoretical point of view, but on a pratical one...

 ata December 8, 2009 03:34

pimpleFoam help

Hi ivan
It's OK.
Is your mesh is same in both runs (OF and StarCCM+)? I think may be your mesh is not a good one near separation point.
May you send images of your mesh and velocity and pressure contours? And how much is order of residuals? Are they change or decrease or increase or oscillate?
Best Regards

Ata

 ivan_cozza December 8, 2009 11:49

Quote:
 Originally Posted by ata (Post 239066) Hi ivan It's OK. Is your mesh is same in both runs (OF and StarCCM+)? I think may be your mesh is not a good one near separation point. May you send images of your mesh and velocity and pressure contours? And how much is order of residuals? Are they change or decrease or increase or oscillate? Best Regards Ata
Hi Ata, the mesh is the same for all the calculations. For images, you have to wait at least tomorrow, as in Italy yesterday and today are holydays...

 aldo.iannetti October 7, 2010 15:16

PimpleFoam for Turbulent and Dyn Meshes OF 1.5

1 Attachment(s)
Hi,
Can you please have a look and test my PimpleSoam for turbulent and dynamic meshes for OF 1.5?
Thanks

Aldo

 mmmn036 June 4, 2013 18:14

Channel395

Hello Guys,

I was running a default case channel395 in OpenFOAM using pimpleFoam solver and it runs perfectly. But i put curved bottom wall using blockMeshDict. Than i run the simulation and it shows error-
Foam::error::printStack(Foam::Ostream&) in "/opt/openfoam220/platforms/linux64GccDPOpt/lib/libOpenFOAM.so"

I don't understand why it doesn't work when i modifed the bottom wall as curved form.

Help will be appreciated

Manjura

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