
[Sponsors] 
February 12, 2016, 05:59 
Minimum possible element size

#1 
Member
Join Date: Nov 2014
Posts: 36
Rep Power: 11 
Hi,
I have a question relating minimum element size that can be used in CFD. I understand that there are problems in microscale where the hypothesis of continuum can not be used. For example, for gases, in a system which has length scale of the order of hundreds nanometers (i.e. comparable to the mean free path). But if I have a macroscale system, where I can get appropriate solution by means of finite volume method, is there a limit of how small elements I can use in discretization? Can I have a minimum element width on the order of nanometers and still get the "right" solution, even though the balance equations I solve for those small elements do not in fact apply on them? 

February 12, 2016, 06:12 

#2  
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,810
Rep Power: 72 
Quote:
In principle, when you work in the nondimensional form of the equation, the domain has computational lenghts of O(1), therefore no matter about the computational precision. As you stated, the limit is in the respect of the continuosu model, I suppose in standard condition no smaller than O(10^8) meters 

February 12, 2016, 09:01 

#3 
Super Moderator
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,412
Rep Power: 49 
Given enough computational resources and leaving aside the problems with roundoff errors, you can use cell/element sizes much smaller than the mean free path and still get the correct solution to the macroscopic set of equations you are solving.
A numerical algorithm for solving the NavierStokes equations is completely unaware of the physics that these equations fail to describe. 

February 12, 2016, 13:50 

#4  
Member
Join Date: Nov 2014
Posts: 36
Rep Power: 11 
Quote:
Is that true even if I use turbulent models? I think viscous heating might not be handled well in such cases ... 

Tags 
element size, finite volume method 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
[ANSYS Meshing] Element size definition of Tetrahedral mesh  soes  ANSYS Meshing & Geometry  0  October 6, 2015 08:07 
[ANSYS Meshing] Minimum Element Size in Design Modeler?  abouma  ANSYS Meshing & Geometry  0  June 26, 2015 09:39 
Solution diverge with small element size.  stone123  FLUENT  4  October 26, 2013 05:48 
[ANSYS Meshing] max mesh element size  ulalala  ANSYS Meshing & Geometry  8  January 20, 2013 17:30 
[ICEM] Global Element Seed Size? Tetra meshing issues  info_bahaider  ANSYS Meshing & Geometry  0  November 28, 2011 08:12 