CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM (http://www.cfd-online.com/Forums/openfoam/)
-   -   Convergence problems with Steady-State algorithms (http://www.cfd-online.com/Forums/openfoam/99243-convergence-problems-steady-state-algorithms.html)

andrea034 March 29, 2012 08:07

Convergence problems with Steady-State algorithms
 
4 Attachment(s)
Dear all,
I am running a simulation with a simple Naca airfoil invested by a flow (60 m/s) in a long and narrow domain.
I imposed cyclic BCs on the upper and lower bound to simulate a blade cascade.
The problem is due to the fact that, using Steady-State algorithm such as rhoSimpleFoam,
pressure residuals don't reach the desidered magnitude.
I've tried different Inlet/Outlet boundary conditions, different schemes, different relaxation factors and
to initialise the field in various ways (using for example potentialFoam and applyBoundaryLayer)
but the result is always the same.I've used both OF2.0 and OF2.1.x.
Further details:
-checkMesh is ok
-for lower speed (10-20 m/s) residuals are ok.
Any suggestion?
Thank you in advance!

flowris March 30, 2012 02:48

You can try more under-relaxation. Or us the SIMPLEC algorithm (rhoSimplecFoam).

andrea034 April 2, 2012 03:37

Thank you for your answer!
I've tried both of them but unfortunately without any significant improvement!

linnemann April 2, 2012 07:08

Hi

Can you try and change the cyclic's to slip BC's?

There can (from my experience) be some stability issues with the cyclic being placed this close to a wall(foil).

Also a zoom on the foil with the mesh enabled would be nice just to see what kind of resolution you have and how many cells there are between the foil and the symmetryPlane.

andrea034 April 3, 2012 10:43

I tried the same airfoil in a larger field with slip BCs and that case reached the convergence easily...Unfortunately I must impose the cyclic BCs (I am simulating a blade cascade) and I can't enlarge the domain.

Actually I can't show you a screenshot of my mesh but there are at least 60-70 cells between the foil and the upper (or lower) boundary.

Based on your experience, could it be a good call trying to simulate the same case (same BCs) but with 3 airfoils in a 3 times larger domain?Or is it totally useless?
Thank you for help!
andrea

andrea034 April 13, 2012 05:10

Dear all,
doubling the domain (and the number of airfoils) all the parameters finally reached the convergence quite easily.
I write this additional post in case someone will have to deal with similar problems.
I' d like to thank flowris and linnemann for their support.
Andrea


All times are GMT -4. The time now is 01:58.