CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

Mesh problem

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

Reply
 
LinkBack Thread Tools Display Modes
Old   May 16, 2005, 12:48
Default Mesh problem
  #1
tuks
Guest
 
Posts: n/a
Hi everyone,

I am solving the flow in a cuboidal shape tank with rectangular c/s inlet & outlet. There is one problem

The area avg velocity@inlet & outlet are different from each other and also from actual velocity given as B.C at inlet.

(1)When i use the unstructured mesh i noticed that the avg velocity @inlet is less while @outlet is more than the specified B.C e.g. From POST, area avg V @inlet=0.002371 and @outlet=0.00261 while B.C is v=0.0025 by parabolic profile.

When i increase the surface resolution by refining mesh at both inlet & outelt, then velocity differences w.r.t B.C. is become more than earlier.

(2)For the structured mesh, when mesh at inlet & outlet surface is refined then velocity values come closer to but not equal to B.C. This happens upto certain level of refinement of mesh, beyond which solver ends with ERROR FINEMESS, fatal overflow.

Can anybody suggest what will be the ultimate solution? Is it necessary to refine mesh in rhe domain, rather making very fine at inlet & outlet.

IMP:: The profile@inlet, plotted by post is slightly different than given by CEL expression.

Thanks in advance

tuks
  Reply With Quote

Old   May 16, 2005, 18:22
Default Re: Mesh problem
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

It sounds like you have not yet got a fully converged solution, and possibly not yet reached grid independance. What are your residuals and imbalances? What physics are you using?

Regards, Glenn
  Reply With Quote

Old   May 17, 2005, 00:09
Default Re: Mesh problem
  #3
tuks
Guest
 
Posts: n/a
hi Glenn,

The solution is converged well, the solver finished as RMS values are below 1e-08. For grid independent solution, i had used two mesh sizes, the sloution was quantitatively different but qualitatively same .

What is mean by grid independence? Is it using different mesh sizes (i.e edge lengths) or using same mesh size but refining the mesh in the region where variables variation is more? Can you specify clearly? I am trying to get avg values of velocity @inlet & @outlet to be same and be closer to the B.C. given at inlet..

Thank you again Glenn.

Tuks
  Reply With Quote

Old   May 17, 2005, 18:41
Default Re: Mesh problem
  #4
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

What do you mean by "quantitatively different but qualitatively the same"? It sounds like you are not yet grid convergent. Try a finer grid.

Glenn Horrocks
  Reply With Quote

Old   May 18, 2005, 14:07
Default Re: Mesh problem
  #5
tuks
Guest
 
Posts: n/a
Thaks Glenn for your good insight. i have been trying with fine grids and i will inform you later, once let me finish with the mesh analysis.

Thak you once again

tuks
  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Dynamic Mesh Problem. Tom Clark FLUENT 9 July 7, 2010 07:56
[GAMBIT] Problem with mesh. Please Help... maziboss ANSYS Meshing & Geometry 1 September 28, 2009 02:24
mesh generation problem Ellen FLUENT 7 February 18, 2009 22:20
mesh control problem TUM CFX 4 July 27, 2001 16:17
Convergence problem when ustructured mesh is used. SangJin Ryu CD-adapco 3 October 5, 2000 20:26


All times are GMT -4. The time now is 18:23.