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-   -   fluent error while iterating (http://www.cfd-online.com/Forums/fluent/41795-fluent-error-while-iterating.html)

Ralf Schmidt July 20, 2006 06:39

fluent error while iterating
 
Hi!

while iterating a 3d inkompressible sim, the continuity residual is increasing almost like linear...

After about 200 iterations (continuity residual is at 10^3) Fluent gives following error:

Error: cx-xy-append-data: invalid number (y)

Error Object: nan

What happend?

Ralf

Razvan July 20, 2006 13:47

Re: fluent error while iterating
 
It is more than sure that you have a setup error in your model. Something like setting unphysically large or small values for boundary conditions parameters, etc. To be able to pinpoint the error I must know exactly what are you simulating and the complete setup of your model. The "nan" message translates into an error that propagates into the equations and it is so large that the numerical alghoritm is not able to dump it, so it grows to infinnity...

Razvan

Ralf Schmidt July 21, 2006 02:11

Re: fluent error while iterating
 
Hi!

Thanks for your answer!

My model: It is 3D, flow inside a square chanel with 60 cylinders parallel to the flow. Perpendicular to the cylinder is a grid (supporting the cylinders), that is modeled as porous zone. The medium is air at 20C and atmospheric pressure. The simulation is isotherm and incompressible (in futur, the cylinder are hot and the flow is cooling them). Flow is turbulent with k-e and std. wall functions.

The geometry is symmetric, so I have 2 walls and 2 symmetrie planes. The inlet is contant mass flow, outlet is pressure outlet. The grid is made from ab. 500.000 tet cells with hex core.

Solver is seggregated. Now, when I turn to coupled solver, the simulation is working, but very slow... also x- and z-vel. residuals are to high (between 1 and 5). But the results seem to be not wrong: right direction of mass flow, wall bc is ok.

So, what do you suggest??

Ther might be something wrong with the grid... the grid check failed and there is now possibility to smooth the grid... maybe thats the error!!

Any ideas??

Ralf

Razvan July 21, 2006 02:20

Re: fluent error while iterating
 
If the grid check really failed, then this could be the problem. Which exactly is the step of the grid checking sequence where it failes (I mean skewness, number of nodes, handedness, etc)?

Razvan

Ralf Schmidt July 21, 2006 05:53

Re: fluent error while iterating
 
Grid Check

Domain Extents:

x-coordinate: min (m) = -3.300000e-01, max (m) = 0.000000e+00

y-coordinate: min (m) = 6.400000e-01, max (m) = 1.700000e+00

z-coordinate: min (m) = -5.250000e-01, max (m) = 0.000000e+00

Volume statistics:

minimum volume (m3): 2.995679e-10

maximum volume (m3): 2.407841e-05

total volume (m3): 1.384525e-01

Face area statistics:

minimum face area (m2): 5.551780e-07

maximum face area (m2): 8.920985e-04

Checking number of nodes per cell.

Checking number of faces per cell.

Checking thread pointers.

Checking number of cells per face.

Checking face cells.

Checking bridge faces.

Checking right-handed cells.

Checking face handedness.

Zone 26: 774900 right-handed, 10 left-handed

Checking element type consistency.

Checking boundary types:

Checking face pairs.

Checking periodic boundaries.

Checking node count.

Checking nosolve cell count.

Checking nosolve face count.

Checking face children.

Checking cell children.

Checking storage.

Done.

WARNING: Grid check failed.

Razvan July 21, 2006 06:04

Re: fluent error while iterating
 
That's clear. There is nothing you can do about this one. You have to start all over again and build a new mesh. If you can send me the .dbs file, maybe I can give yo some advice about that...

Razvan

Ralf Schmidt July 21, 2006 06:25

Re: fluent error while iterating
 
ok... but it is about 150 MB, thats too large for email...

I will try, to put it on our server. But unfortunately thats not possible until monday (admin already at home :(

Thanks a lot for help

Ralf

Razvan July 21, 2006 06:33

Re: fluent error while iterating
 
I meant only the geometry, without the mesh. That should be small enough (no more than a few megabytes), especially if you use an archiver like WinRAR which could reduce the size of the .dbs file up to 5-6 times!

Razvan

pp July 21, 2006 08:38

Re: fluent error while iterating
 
look for repair-face-handednes in grid menu in textual user interface. This could help

reg, pp

Ralf Schmidt July 21, 2006 09:17

Re: fluent error while iterating
 
Hi!

first: the .dbs file is about 150 MB, maybe there is the error...

second: I can not find the "repair-face-handednes" function in fluent. There is no repair option in the text menue (Fluent 6.2.16)

Thanks for help!

Ralf


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