# [GAMBIT] Boundary layer mesh & map mesh in rectangular ribbed channel

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

 November 1, 2012, 10:44 Boundary layer mesh & map mesh in rectangular ribbed channel #1 New Member   shayan Join Date: Jul 2012 Location: Australia Posts: 26 Rep Power: 7 Sponsored Links Hello I have a ribbed rectangular channel with two blocks on upper wall as blow: http://imageshack.us/photo/my-images...hot001rxd.jpg/ I have performed boundary layer mesh as can be seen in the image,but I don't know how to do map mesh for the face!Is it necessary do the mesh for edges first? if so,what will happen for the boundary layer meshes? How can I have a uniform mesh(with rectangular cells)? Thanks shayan

 November 1, 2012, 11:08 #2 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 don't do this unless you want the hybrid mesh. This geometry is easily mappable. Make few split on the straight line and create edge between vertices. Set the no of nodes on vertical edges, grading scheme and ratio of 1.1-1.2 shayan_mv likes this.

November 1, 2012, 11:29
#3
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by Far don't do this unless you want the hybrid mesh. This geometry is easily mappable. Make few split on the straight line and create edge between vertices. Set the no of nodes on vertical edges, grading scheme and ratio of 1.1-1.2
If i do that,I'll have more than one edge in inlet.So, I should define more than one "inlet velocity" as boundary condition and also the same condition for "pressure outlet". Is this OK?!

 November 3, 2012, 04:57 #4 Super Moderator     Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,210 Rep Power: 34 you can define many edges as part of ONE boundary condition. Your domain should be automatically set as mappable. If not, follow Far's advice. If you don't split your domain, enable "internal continuity" option in the boundary layer panel shayan_mv likes this. __________________ In memory of my friend Hervé: CFD engineer & freerider

November 3, 2012, 11:52
#5
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by -mAx- you can define many edges as part of ONE boundary condition. Your domain should be automatically set as mappable. If not, follow Far's advice. If you don't split your domain, enable "internal continuity" option in the boundary layer panel
Thanks Max
I did what you said,and I got the following result:

http://imageshack.us/photo/my-images...shot002td.jpg/

As you can see in the picture, after "map mesh" the mesh is disorder! I can make it fix by making the interval size smaller,but I don't really need to do that.I just want to have denser mesh near ribs and upper wall and to have the rest of face with larger mesh size! what shall I do now,Max?
thank you

 November 3, 2012, 13:36 #6 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 Like this?

November 3, 2012, 13:50
#7
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by Far Like this?
exactly.I want this! How did you do? I'm just beginner ,May I ask you to show me the steps that you have done...
Thank you very much

November 3, 2012, 14:09
#8
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by Far Like this?
I know that there are different techniques of doing the mesh,but I am looking for the one that I can reach convergence in acceptable iteration.And also get good results out of that e.g. velocity vectors, Nusselts Number,...

 November 3, 2012, 14:23 #9 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 First mesh was made in ICEM, which allows me to make the mesh in very few clicks and I just used the O-grid and every thing else is outcome. Whereas the pics below (similar to ICEM mesh) shows the mesh created by Gambit a d requires some geometric operations. Download gambit file from this link : https://www.dropbox.com/s/05034x33i4...ed_channel.dbs shayan_mv likes this.

November 3, 2012, 14:41
#10
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by Far First mesh was made in ICEM, which allows me to make the mesh in very few clicks and I just used the O-grid and every thing else is outcome. Whereas the pics below (similar to ICEM mesh) shows the mesh created by Gambit a d requires some geometric operations. Download gambit file from this link : https://www.dropbox.com/s/05034x33i4...ed_channel.dbs
Thank you so much, I think I should make many faces and mesh each one as I want

regards

 November 3, 2012, 14:44 youtube video being uploaded #11 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 Youtube clip is currently being processed and will post link, once it is done. Every thing was done in gambit, since you are using gambit Last edited by Far; November 3, 2012 at 23:43.

 November 3, 2012, 23:44 #12 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 Youtube video link : http://www.youtube.com/watch?v=CfOGD...ature=youtu.be

November 3, 2012, 23:58
#13
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
Dear Far
The video is not available!

 November 4, 2012, 00:00 #14 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 Yeah, there was some error in uploading and done again. see this link: https://www.youtube.com/watch?v=Gub1Kbcup2k

November 4, 2012, 08:02
#15
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
Thanks a a lot dear Far. I got nearly good results...

My problem was converged after 1428 iteration! May I ask you that what is the main reason? ( I think it is not acceptable)

Regards

Shayan

November 4, 2012, 08:07
#16
Super Moderator

Sijal
Join Date: Mar 2009
Posts: 4,329
Blog Entries: 6
Rep Power: 45
Quote:
 Originally Posted by shayan_mv Thanks a a lot dear Far. I got nearly good results... My problem was converged after 1428 iteration! May I ask you that what is the main reason? ( I think it is not acceptable) Regards Shayan
If results are good then why you are not satisfied? Which version of fluent you are using?

November 4, 2012, 08:11
#17
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by Far If results are good then why you are not satisfied? Which version of fluent you are using?
Well, in comparison with the previous examples that I have done ,my problems were converged less than 300 iteration !

I use "Fluent 6.3.26"

 November 4, 2012, 08:16 #18 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 It was the similar case? If not then we cannot compare them!!! This may be due to mesh problem, specially the transition between different blocks (in gambit it is face). So try to make the mesh as smooth as possible and specially at the different faces boundaries there should be slow transition and same cell size on both sides of common edge. Moreover you should make the dense mesh in the regions where you expect the separation and strong gradients. I also recommend you to make the mesh refinement study by making the successive refined meshes to conclude mesh effects on results. In short: 1. Mesh should be fine enough 2. Should be smooth as possible shayan_mv likes this.

November 4, 2012, 08:32
#19
New Member

shayan
Join Date: Jul 2012
Location: Australia
Posts: 26
Rep Power: 7
Quote:
 Originally Posted by Far It was the similar case? If not then we cannot compare them!!! This may be due to mesh problem, specially the transition between different blocks (in gambit it is face). So try to make the mesh as smooth as possible and specially at the different faces boundaries there should be slow transition and same cell size on both sides of common edge. Moreover you should make the dense mesh in the regions where you expect the separation and strong gradients. I also recommend you to make the mesh refinement study by making the successive refined meshes to conclude mesh effects on results. In short: 1. Mesh should be fine enough 2. Should be smooth as possible
OK. Thank you very much. you guide very exact. I appreciate that.

I just could not get:
1. "Nusselt Number" plot against "Re or Position"
2. " Friction factor" plot against "Re"

 November 4, 2012, 08:38 #20 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,329 Blog Entries: 6 Rep Power: 45 Refer to some good reference see where they plotted these values or on which plane or line? Then this can be done in Fluent or CFD-post or techplot! shayan_mv likes this.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Bigio ANSYS Meshing & Geometry 32 January 9, 2014 11:26 Luigi_ STAR-CCM+ 7 January 15, 2012 15:40 Luigi_ Main CFD Forum 0 December 14, 2011 14:42 rohitjvbibin Main CFD Forum 0 March 5, 2011 12:28 Arnoldinho OpenFOAM 1 January 22, 2011 05:31