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

A doubt on grid independence study

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 14, 2000, 00:37
Default A doubt on grid independence study
  #1
G.Balakrishnan
Guest
 
Posts: n/a
I am working with wall functions with k-epsilon model. i am studying the wall heat transfer. With wall function approach, it is said that the boundary y+ should be about 30. So i maintained that and got some result.Now for doing grid independence, i halved each cell except the wall-nearest cells.i got a slightly different result..So i again halved all the cells except the wall-nearest cells to study grid independence..Now it became that the wall cells are larger than the ones away from the wall..Is it ok..What is the effect of this.. Any help is welcome.
  Reply With Quote

Old   November 14, 2000, 03:24
Default Re: A doubt on grid independence study
  #2
Rüdiger Schwarze
Guest
 
Posts: n/a
When You calculate heat transfer problems, You must resolve two boundary layers: The momentum boundary layer and the thermal conduction boundary layer. The thickness of these two layers is, in general, different. In fluent, You fit the grid resolution only to the momentum boundary layer, thus the turbulent heat transfer may differ when You change the grid resolution.
  Reply With Quote

Old   November 14, 2000, 05:10
Default Re: A doubt on grid independence study
  #3
G.Balakrishnan
Guest
 
Posts: n/a
My doubt is whether the wall funciton approach is enough when we study heat transfer to the wall or is there a need to go to the two-layer zonal model (fluent 5.3). with regards,
  Reply With Quote

Old   November 14, 2000, 05:31
Default Re: A doubt on grid independence study
  #4
Rüdiger Schwarze
Guest
 
Posts: n/a
You should check first the non-dimensional thickness of the momentum (y^*) and thermal (y_T^*) boundary layers. In case of y^* < y_T^*, fluent uses a linear law in order to compute the heat flux through the thermal boundary layer, independent of the near-wall resolution of Your grid. Otherwise, You can try the two-layer model. Also try the RNG-k-eps turbulence model with the refined description of heat transfer.
  Reply With Quote

Old   November 21, 2000, 12:05
Default Re: A doubt on grid independence study
  #5
Narayanan
Guest
 
Posts: n/a
hi i am also from iit madras. i have done grid independence study. first of all r u using fluent. for grid independence, dont try to play with cells near the walls. just double the no of cells by changing the scale factor in meshing option. then solve for both grids. most of the time dont try with convergence level but go for many no of iterations.
  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
how to do a grid independent study xyq102296 ANSYS 6 January 22, 2014 01:13
Grid Independence Calculations gpb FLUENT 0 October 5, 2007 00:22
Grid independence check Mattis Voss FLUENT 1 November 23, 2005 11:30
Grid refinement study smoothsword Main CFD Forum 4 January 2, 2004 17:07
Combustion Convergence problems Art Stretton Phoenics 5 April 2, 2002 05:59


All times are GMT -4. The time now is 00:03.