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Convergence problems with Steady-State algorithms

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Old   March 29, 2012, 08:07
Default Convergence problems with Steady-State algorithms
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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!
Attached Images
File Type: png naca.png (2.6 KB, 48 views)
File Type: png snapshot6.png (8.9 KB, 61 views)
Attached Files
File Type: txt fvSchemes.txt (2.0 KB, 26 views)
File Type: txt fvSolution.txt (2.5 KB, 22 views)
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Old   March 30, 2012, 02:48
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You can try more under-relaxation. Or us the SIMPLEC algorithm (rhoSimplecFoam).
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Old   April 2, 2012, 03:37
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Thank you for your answer!
I've tried both of them but unfortunately without any significant improvement!
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Old   April 2, 2012, 07:08
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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.
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Old   April 3, 2012, 10:43
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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
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Old   April 13, 2012, 05:10
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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
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