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

boundary layer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   November 23, 2005, 03:43
Default boundary layer
  #1
Fer
Guest
 
Posts: n/a
Hi all! I'm trying to simulate the flow over a car in 2D. I'm using Tri elements for the mesh (run in Gambit). My doubt is that I don't know the convenience or not in using boundary layers to define the mesh in those regions closer to the car's surface. Can anybody give me advise about it and, in that case, the criterion to select the thicknes of that boundary layer?

Thanks all, again

Fer

  Reply With Quote

Old   November 23, 2005, 05:25
Default Re: boundary layer
  #2
bharat
Guest
 
Posts: n/a
hi Fer, If u r not comfortable with boundary layers..u can go ahead with meshing the edges and then proceed towards meshing the face. The best thing is to divide the geometry into sections and then mesh. Using boundary layer is always best because it gives u total control over the thickness of the cells near the boundary. For estimating the grid spacing..it depends on the turbulence models...that is either u r going for y+ <1 or y+>30 U can estimate it by using the following link http://geolab.larc.nasa.gov/APPS/YPlus/

hope this helps

bharat
  Reply With Quote

Old   November 23, 2005, 05:49
Default Re: boundary layer
  #3
Fer
Guest
 
Posts: n/a
Thanks very much bharat,

I have made some things you told me in your post: dividing the whole geometry into different pieces (to control better the mesh) and calculate the ds distance (function of y+, Reynolds,...). I have used a K-e+RNG turbulence model and Standard Wall Treatment (and also Non-Equilibrium), so in that case y+ is recommended to be in (30,300) (better in (30,150)). After simulating this y+ parameter plotting fits quite well with that recommendation. The doubt is if the shape of the boundary layer (with edges more aligned at the flow near the walls than the Tri elements) works better than meshing with those Tri elements until the wall surface.

Thanks with your help again,

Fer

  Reply With Quote

Old   November 23, 2005, 11:27
Default Re: boundary layer
  #4
Anindya
Guest
 
Posts: n/a
Try to use a boundary layer mesh using quad elements around the car body (walls). The distance upto which you should use a B.L. mesh depends on the problem, specially velocity. You can choose a couple of distances. For the rest of the domain use a tri mesh as you are using. Also you can use y+ adaption if your initial B.L. y+ is higher or lower than what you need. As you are doing a 2D case, trying a few different grids with different B.L. thickness would not take much time.
  Reply With Quote

Old   November 24, 2005, 04:12
Default Re: boundary layer
  #5
Fer
Guest
 
Posts: n/a
The last question,

I suppose that using boundary layer of quad elemets aruound the car body and Tri mesh for the rest supplies better results than Tri mesh for the whole fluid area, but does it improve the convergence process?

Thanks bharat and Anindya for your help

Fer

  Reply With Quote

Old   November 24, 2005, 10:37
Default Re: boundary layer
  #6
bharat
Guest
 
Posts: n/a
Hi Fer, I think using quad elements at the boundary would reduce the number of cells as compared to tri elements. I think it should not affect the convergence (open to doubt).

hope this helps bharat
  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
Default Faces on Boundary Layer axel Open Source Meshers: Gmsh, Netgen, CGNS, ... 8 February 17, 2011 07:47
Boundary Layer Question scottneh STAR-CCM+ 3 September 30, 2010 14:21
Adapt mesh without modifying boundary layer cells? Freeman FLUENT 0 February 22, 2009 14:11
3D Boundary Layer Mario FLUENT 0 February 17, 2009 03:40
Trimmed cell and embedded refinement mesh conversion issues michele OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 2 July 15, 2005 04:15


All times are GMT -4. The time now is 12:00.