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Rishikesh September 15, 2008 04:01

I am doing cfd analysis of an air gap in a foil bearing used in turbomachines.While solving the mesh in fluent,when i put 'compute from' in the initialization panel,it reads non-positive volumes exist.

What is the solution for the problem i am encountering?

Reply eagerly awaited.


CL September 15, 2008 06:14

Re: Query
Hi rishikesh check ur grid first, i think u may have negaive volume in ur domian thats why its showing like that. X,Y grid should be in positive value suppose if its in negative means fluent cant solve that...

Rishikesh September 15, 2008 06:20

Re: Query
Dear CL

when we put up grid check in fluent,if it says done,does that mean that the grid is correct?

i have already used smoothing during meshing in gambit.

please elaborate a bit on 'negative volumes' and how are they created?

my meashing area is really small(350 microns) as compared to the circumference.

could this be a reason why negative volumes are being created?

CL September 15, 2008 06:59

Re: Query
Hi rishi, A negative value for the minimum and maximum volume indicates that one or more cells have improper connectivity. So check ur grid in that see minimum and maximum volume, check whether its showing positive value or negative value.

Rishikesh September 16, 2008 01:31

Re: Query
Dear CL

i checked the min and max volunme values.both are positive.still it is showing 'non-positive values exist'.

what would be the problem now?

Venkatesh V September 16, 2008 02:30

Re: Query
Hi Cl and Rishikesh,

I have got one more query though not related to yours, it is related the problem you are simulating. In the bearings usually the gaps will be in the order of microns. In that case surface tension effects will play a major role and the surface roughness will be in the order of our mesh size.

Do you have any puplished literature on CFD analysis using fluent on bearings? If you have documents can share it with me.

Thanks Venkatesh V

Rishikesh September 16, 2008 02:33

Re: Query
hey venkatesh there is very less literature available on bearing cfd.

i do have come pdf files

gimme your email and i will forward it to u

and yes your point about surface tension seems to be correct.

Rishikesh September 16, 2008 06:02

Re: Query
venkatesh i am about to complete the 1st trial for my foil bearing. ucan ask me if u hv any difficulties.....


Rishikesh September 16, 2008 06:04

Re: Query
Hey CL

the problem is solved

thnx a ton for your help.

CL September 16, 2008 06:07

Re: Query
Hi rishi, can u tell me what was the reason of the problem pls.

With regards, CL

Rishikesh September 16, 2008 06:12

Re: Query
well the reason was that i was not re-ordering the domain when i read the case file in fluent Rishikesh

Rishikesh September 17, 2008 01:15

Re: Query
hey venkatesh have u done cfd analysis of any bearing? please reply asap


Rishikesh September 18, 2008 01:02

Re: Query
CL can u tell me how to import an igs file into gambit?

CL September 18, 2008 03:33

Re: Query
Open the gambit- file- import-geometry- iges file.

Rishikesh September 18, 2008 04:08

Re: Query
i tried it.its saying translation failed.

is it possible to import a geometry in a pirated version?

CL September 18, 2008 04:31

Re: Query
Tell me in which modeeling software u modeled ur geometry.

Rishikesh September 18, 2008 04:40

Re: Query
hey CL

i was able to import the geometry. but since i am using a pirated version,i can only use the native mode.

btw,i created the geometry in SOLID EDGE

thanks a lot for your help!


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