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

about first layer thickness

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 24, 2007, 06:47
Default about first layer thickness
  #1
Eric
Guest
 
Posts: n/a
Dear Friends,

I am using CFX-mesh to make the mesh. Could you tell me how to decide the first layer thickness?

The fluid in my simulation is compressible.

Thank you in advance.

Eric
  Reply With Quote

Old   January 24, 2007, 10:55
Default Re: about first layer thickness
  #2
Alejandro
Guest
 
Posts: n/a
Hi Eric,

What geometry are you simulating? A way to compute the thickness of the first elements near a wall is to estimate the height of the boundary layer. It depends on the geometry, but for example for airfoils, a good rule of thumb is to approximate the boundarylayer height, as the height of the BL for a flat plate, if your Re number is high enough so that you are in a turbulent regime, then the thickness can be estimated as d=0.14*Re^(-1/7)

So you capture the effects of the viscous sublayer, you should fit at least 15-20 elements within the BL, so a a good guess for the thickness of the first layers would be d/20 (20 extrusion layers, with a small expansion factor).

To decide if your choice is correct, you can also check the y+ values and compare with the ranges advised for the different turbulence models.

I hope it helps. Best regards,

AG.

  Reply With Quote

Old   January 24, 2007, 11:35
Default Re: about first layer thickness
  #3
John
Guest
 
Posts: n/a
Hi,

When you define the inflation layers in cfx-mesh, you can input the Y+ value and the Reynolds number of flow. The CFX-mesgh will automatically generate a first layer which can meet your requirements.

Regards,

Jone
  Reply With Quote

Old   January 24, 2007, 22:58
Default Re: about first layer thickness
  #4
Eric
Guest
 
Posts: n/a
Thank you very much. I will try it.

  Reply With Quote

Old   February 4, 2007, 10:29
Default Re: about first layer thickness
  #5
Eric
Guest
 
Posts: n/a
Dear Mr.Alejandro Thank you for your answering on the www.cfd-online.com about the thickness of Bounday Layer. Could you tell which book included this formula and the theory? Because I need reference to finish my paper. Thank you in advance.

Best Regards Eric

My e-mail: qiuyifa@hotmail.com
  Reply With Quote

Old   February 5, 2007, 06:08
Default Re: about first layer thickness
  #6
Alejandro
Guest
 
Posts: n/a
Hello Eric,

you can find reference to that formula (although the factor listed there is 0.16 instead of 0.14) in "Fluid Mechanics" White, F.

The chapter of interest is "Flow Past Immersed Bodies"

Best Regards, Alejandro.
  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
SnappyHexMesh - no layer added bejbro OpenFOAM Mesh Utilities 4 October 16, 2014 20:24
Total Thickness of Inflation Layer prikeyma CFX 3 February 12, 2013 04:19
Boundary layer in a pipe Clementhuon OpenFOAM Native Meshers: snappyHexMesh and Others 6 March 12, 2012 14:41
Boundary layer generation problems ivan_cozza OpenFOAM Native Meshers: snappyHexMesh and Others 0 October 6, 2010 14:47
errors Fahad Main CFD Forum 0 March 23, 2004 14:20


All times are GMT -4. The time now is 07:01.