CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > Siemens

cell size

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   November 24, 2005, 07:45
Default cell size
Posts: n/a
hi when i am making trimmed mesh, what is maximum and minimum cell size i have to give. for the same problem i am getting converged solution with some value of max and min cell size, but if it changes i am not getting convergence. what is the optimal cell size recommended in star-cd. Thanking you with reg Baskar
  Reply With Quote

Old   November 24, 2005, 08:41
Default Re: cell size
Posts: n/a
how long is a piece of string?
  Reply With Quote

Old   November 25, 2005, 23:58
Default Re: cell size
Posts: n/a
Baskar, you have just hit upon one of the problems of CFD. Just because something may work, doesn't mean it is correct. There are a couple of best practices you might want to check out.

Basically, when building a mesh for a problem a mesh sensitivity study is done. The mesh size is increased until the answer doesn't change, then go back to the smaller mesh size that gives the same answer. Different kinds of problems have different mesh size requirements.

  Reply With Quote

Old   January 17, 2006, 12:04
Default Re: cell size
Posts: n/a
Tom, you are quite right. Can you please suggest me the steps to carry out mesh sensitivity study for a problem? What parameters i need to focus for one-to-one comparison.

Actually i want to carry out a comparative study of cell-size effect as well as cells-type ( Hexa, Pyramid, tetra etc. ) effect for a fixed problem.

Thanks in advance

  Reply With Quote

Old   January 18, 2006, 13:34
Default Re: cell size
Tom Keheley
Posts: n/a
Siddharth, the ERCOFTAC best practices recommends that for each class of problem a grid dependency study be performed. They recommend using three grids that are signficantly different in grid size, where ideally you double the grid twice in each direction and then apply the Richardson extrapolation (P.J. Roache(1997), "Quantification of Uncertainty in Computational Fluid Dynamics," Annual Review of Fluid Mech., Vol.29, pp 123-160).

What is interesting is that sometimes it is not the entire grid that is important. I just finished a study where with one grid size it took 5000 iterations for the residulas to converge to E-04. I did a grid refinement on just one section of the mesh and the problem converged to residuals of E-06 in 1500 iterations and agrred with the test data.

I hope this helped. Tom
  Reply With Quote


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Limit on maximum cell size to minimum cell size ratio albcem OpenFOAM Running, Solving & CFD 2 October 17, 2011 12:00
the 1st cell size from Y+ ken Main CFD Forum 0 December 11, 2005 08:56
cell size Sam FLUENT 2 March 11, 2005 03:33
cell size solomon Main CFD Forum 0 May 17, 2003 13:52
Cell size Roued Siemens 1 November 22, 2001 05:13

All times are GMT -4. The time now is 20:32.