
[Sponsors] 
December 8, 2011, 04:47 
Why is Fluent unable to deal with my model at the micron scale?

#1 
New Member
Join Date: Dec 2011
Posts: 9
Rep Power: 5 
My model is a micro turbo rotor spinning in a cylindrical wall. When I scaled the grid by setting the scale factors of xyz to be 0.00001 or lower, the iteration would stop in one step, saying "solution is converged"
At first i thought something was wrong with my grid and settings, so i created a cylindrical pipe model where liquid flows in with a speed magnitude equal to that of the radius through the bottom and out through the top, but this model has the same problem that when the scale factors of xyz are lower than a certain value (0.0009 here), the iteration stops within one or a couple of steps. however, what has puzzled me is that when the scale factors are greater than a certain value (1e5 for my rotor model and 0.0009 for the pipe one), the problem doesn't show up and Fluent gives a good solution. so can Fluent deal with models as small as tens of microns? 

December 8, 2011, 06:04 

#2  
Senior Member

Quote:
Did you disable convergence criteria in "solve>monitor>residual" ? It better to use double precision version for your purpose and also, you can change length dimension to "mm" for example but as you said, this problem may exist even in double precision solvers if the variables would be in the order of round off error which is about 1.0e16. As there are many simulations with FLUENT for micro channels in literature, I don't think that this can make any issue for your case. But if you couldn't solve this problem, maybe a dimensional analysis can help. Bests,
__________________
Amir 

December 8, 2011, 14:39 

#3  
New Member
Join Date: Dec 2011
Posts: 9
Rep Power: 5 
Quote:


December 8, 2011, 15:31 

#4  
Senior Member

Quote:
I meant toggle off "check convergence" in "solve>monitor>residual"; in this manner you never face "solution is converged"!!! just let it continue to iterate. Bests,
__________________
Amir 

December 9, 2011, 00:39 

#5 
New Member
Join Date: Dec 2011
Posts: 9
Rep Power: 5 
Sorry, I'm a newb so i didn't quite understand what you'd meant as well as some of those variables and settings. Your suggestion did work, and i think what i should do now is optimize the grid. Thank you very much for you kind help.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Use of kepsilon and komega Models  Jade M  Main CFD Forum  12  June 2, 2015 13:16 
Superlinear speedup in OpenFOAM 13  msrinath80  OpenFOAM Running, Solving & CFD  18  March 3, 2015 06:36 
selfbuilt model embeded in FLUENT  Jiedong  FLUENT  0  January 22, 2009 03:57 
Modeling in micron scale using icoFoam  m9819348  OpenFOAM Running, Solving & CFD  7  October 27, 2007 00:36 
Can FLUENT model flashing liquids?  SWK  FLUENT  4  December 13, 2005 22:55 