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

nodes number within boundary layer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 4, 2005, 20:17
Default nodes number within boundary layer
  #1
Gab
Guest
 
Posts: n/a
Hello,

As discussed in previous posts about SST model, sufficient nodes(5-20) are needed for boundary layer.I was wondering how to DIRECTLY check the nodes number in CFX to make sure that sufficient nodes are provided in boundary layer. In cfx-post? How to do that?

Can someone explain this? Thanks!

regards!

Gab
  Reply With Quote

Old   July 5, 2005, 05:51
Default Re: nodes number within boundary layer
  #2
Paul
Guest
 
Posts: n/a
Hi Gab,

The easiest way is to create a plane in CFX post which cuts through the boundary layer you are interested in. Under the "render" tab for the plane select "draw lines", this will display the mesh that is coincident with the plane. Colour the plane with the velocity tangential to the surface.

This will visualise the boundary layer and the mesh, you can then simply count the number of points in the boundary layer region.

Cheers

Paul
  Reply With Quote

Old   July 5, 2005, 10:03
Default Re: nodes number within boundary layer
  #3
Gab
Guest
 
Posts: n/a
Thanks a lot, Paul

Best regards!

Gab
  Reply With Quote

Old   July 5, 2005, 10:46
Default Re: nodes number within boundary layer
  #4
Gab
Guest
 
Posts: n/a
Hi, Paul

I am still not sure what you mean 'Colour the plane with the velocity tangential to the surface'. Do you mean to show the mesh and the velocity contour in the same plane or in different planes?

I just tried to show the mesh and velocity contour in one plane. In some regions I can see the great color difference between wall areas and main flow(Is this the way to identify the boundary layer?). However in other regions, no obvious color difference. How to understand this?

Thanks again!

Gab
  Reply With Quote

Old   July 5, 2005, 11:16
Default Re: nodes number within boundary layer
  #5
Paul
Guest
 
Posts: n/a
Hi Gab,

You've done it correctly, show the mesh and velocity in the same plane.

The boundary layer is the region where you see the colour change as you approach the wall. Depending on the turbulence model you are using you should have between 10 and 15 node points to resolve this area.

Where you are seeing no change in contour level near the wall: If the wall boundary condition is "no slip" then the velocity at the wall is zero. I assume you have some free stream velocity so there must be a gradient there somewhere.

What is the situation you are trying to model?

Regards

Paul
  Reply With Quote

Old   July 5, 2005, 12:57
Default Re: nodes number within boundary layer
  #6
Gab
Guest
 
Posts: n/a
Hi, Paul.

I appreciate your quick reply and helpful comments. Now I have understood how to ckeck the nodes number.

I am working on a multiphase modelling (gas and water) and always not able to reach sufficient converge level. So I am trying to refine my mesh and change turbulence model from k-e to SST.

The locations that have no change in contour level near the wall were set as "free slip" boundary condition. So it should be normal.

Thanks again!

Regards!

Gab

  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
Boundary layer in a pipe Clementhuon OpenFOAM Native Meshers: snappyHexMesh and Others 6 March 12, 2012 13:41
[GAMBIT] 3D boundary layer and meshing problem in GAMBIT 2.4.6 prashanthreddyh ANSYS Meshing & Geometry 1 December 20, 2011 00:35
external flow with snappyHexMesh chelvistero OpenFOAM 11 January 15, 2010 19:43
RPM in Wind Turbine Pankaj CFX 9 November 23, 2009 04:05
Boundary Layer Flow Paradox Wen Long Main CFD Forum 3 September 24, 2002 08:47


All times are GMT -4. The time now is 20:22.