Convergence problems turbo machinary
hi,
i have a modell devided by 4 (90°) my MAX residuals are never under e-02. coupled rotating domain with stationary domain. air as ideal gas / total energy. physical time step 0.00001. interface between domains frozen rotor. can some one help me to get an convergence? thanx |
export the residuals (CFX-Pre) within the normal result files->solve again starting from your current solution and run just 1 Iter.->visualize the "highest" residuals in CFX-Post as a Isovolume --> i bet youŽll find some mesh issue OR some trans. effect
Is there a part. reason for chossing such a small physical TS? neewbie |
Yes if not such a ts, error comes 'overflow'
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tried 'local' timestepping?
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thanx :D for quick answers
no physical ts |
what kind of turbomachinery? turbine?
you'vve to provide more information to achieve serious advice. as it is a stationary simulation, it's not a "real" timestep, but rather a pseudo. if your mesh has good quality, stat/rot interface is well placed and there were no setup failure (e.g. neglect wall as counter-rotating etc.), try to use a 1st order scheme (also turbulence) or try to use a coarse mesh to achieve convergence. is there also a diffuser anywhere?! |
yes it is a stationary simulation. no turbine. it is a asynchrone machine. i am solving the inner convetive cooling... air produces also heat. my mesh has a good quality but could be better. the geo is very difficult. the inter face i ok ( frozen rotor) no countering wall exist.
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can you send an image of your residuals?
are they like a smooth line or not? are they changing? and also you should check your results if they are logical residual is not a big deal |
Which wall function should be taken? CFX makes it automatically??
what about les ? |
Quote:
One for sure: you need a very good mesh for this kind of simulation. y+ should be <1! that means, that you can't use a wall function. use sst as turbulence model and ensure, that your near-wall boundary layer is resolved accurate. regarding heat transfer issues, you have to be meticulous about that! y+ values currently? please provide some pics |
Sorry to jump in late but the original question here is an FAQ: http://www.cfd-online.com/Wiki/Ansys...gence_criteria
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ghorrocks i read this time ago. i did not ask before reding this. so i am refinig the mesh.
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As I mentioned before (after looking at your residuals), you have problems with energy equation. It's highly proable that you didn't resolve boundary layer accurate and/or use heat model, that doesn't apply to real physics.
But it's difficult to give serious advice without further details. What kind of mesh do you use? what y+ values do you have? which setup do you use? Quote:
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my mesh is patially stuctured, partially unstructured. but some geom is nor possible to mesh it with icem (to much time). i do not unterstand the setup? what do you mean with this?
my physical ts is 1*e-6 now is this ok or to small? |
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