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-   -   Grid check failed (http://www.cfd-online.com/Forums/fluent/27741-grid-check-failed.html)

Ellen June 21, 2000 17:08

Grid check failed
 
Hi, I created my grid file in I-DEAS, and then imported into Fluent for computation. Just after importing the grid, the "Grid check" command didn't find anything wrong, but after I finished the initialization, there was a warning saying non-positive volumes exist, and this time the grid check also failed, stating that many elements are lefthanded and many nodes lie below the axisymmetric axis. (my computation involved a mass-flow-inlet and a pressure-outlet, and I chose mass-inlet as initialized point.)

I can't figure out where I've gone wrong, if anyone could give me some hint or help, I'd be very grateful.

Sandeep June 21, 2000 17:16

Re: Grid check failed
 
For the nodes lying below axisymmetric axis..try a grid translate option in fluent. If ur problem is axisymmetric about X..use Y translate =0.00001 (basically a small value). I had the same problem once with this error and it worked.

For lefthanded cells

do this..

> grid
> modify zones
> repair face handedness

Try this might work..!


Jack Keays June 22, 2000 09:44

Re: Grid check failed
 
I alos had the problem with non positive volumes. They only seem to materialise after I initialze. I don't experience any face nadedness problems though. Do you know why fluent suddenly found or created volumes with non positive sizes???

Kai Kang June 22, 2000 12:27

Re: Grid check failed
 
I've had this problem, too, when I was generating the grid using Gambit for both hex- and tet- elements. I do not know any reason why, but there is also a grid check in Gambit which is very helpful in finding out which volume in your model is wrong---most of the time I try to change the interval assignments and remesh the volume.

Ellen June 22, 2000 12:27

Re: Grid check failed
 
Thanks a lot, Sandeep, I solved this problem by translating my grid a little bit along Y direction. and it seems that if there're nodes lying below the axis for the axisymmetric problem, then non-positive volumes will arise by revolving such nodes, and at the same time cell lefthandedness appears also.

thanks again, all.

Sandeep June 23, 2000 14:42

Re: Grid check failed
 
..well sometimes little things like this just happen..!I am so glad we have this discussion forum..!

sarat2d June 18, 2009 14:56

Negative volumes for axisymmetric cases
 
this is beacuse I think Fluent wants the non-symmetric variable as positive,

i.e. if the case were symmetric about X, then the values of Y must all be positive, for meshing and grid check. So you must translate the grid in Y such that the minimum and maximum valeus of Y are both >0.

Dont know why this is.

sri99iitm April 26, 2010 09:12

can we start simulation though gird check fails????
y grid checking fails actually???


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