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

Boundary Layer Low Re Turbulent Flow

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 5, 2013, 10:52
Question Boundary Layer Low Re Turbulent Flow
  #1
Member
 
Join Date: Apr 2011
Posts: 55
Rep Power: 14
Ruonin is on a distinguished road
Hi folks,

I'm implementing a Low Re k-ep model and, as mentioned in the forum on several occasions, I have to refine the mesh heavily near the wall.

I have a boundary layer, and I have used the CFD tools for accessing the distance for the first layer. In my case it's 5E-6 m, which I think is very close to the numeric minimum value of the software.

My question is this: as I refine the mesh near the wall, I get a problem in the convergence. The k and ep variables just stall at a certain residual value.

Has anyone experienced this?

Best Regards,

Rui Silva
Ruonin is offline   Reply With Quote

Old   February 7, 2013, 01:36
Default
  #2
New Member
 
Mohammed
Join Date: Feb 2013
Posts: 12
Rep Power: 13
Mohd123 is on a distinguished road
Maybe you have reached convergence if stall at high residual value.

At what residual value it stalls before refining and after refining?
Mohd123 is offline   Reply With Quote

Old   February 7, 2013, 08:30
Default
  #3
Member
 
Join Date: Apr 2011
Posts: 55
Rep Power: 14
Ruonin is on a distinguished road
Thank you for your reply Mohd123,

Before refining I get to about 10^-3 residual (standard for COMSOL) and after refining the value is about 10^-2.

Could it be that the boundary layer mesh is to fine and causing numerical diffusion?

Best Regards,

Rui

Quote:
Originally Posted by Mohd123 View Post
Maybe you have reached convergence if stall at high residual value.

At what residual value it stalls before refining and after refining?
Ruonin is offline   Reply With Quote

Old   February 8, 2013, 06:06
Default
  #4
New Member
 
Mohammed
Join Date: Feb 2013
Posts: 12
Rep Power: 13
Mohd123 is on a distinguished road
The best thing I suggest to do to make sure that mesh is totally independent of solution is to do a Grid Independence Study, so that you keep refining the mesh (from course to fine) until you reach a contant solution and the more you refine the mesh the solution will be constant.


Quote:
Originally Posted by RSilva View Post
Thank you for your reply Mohd123,

Before refining I get to about 10^-3 residual (standard for COMSOL) and after refining the value is about 10^-2.

Could it be that the boundary layer mesh is to fine and causing numerical diffusion?

Best Regards,

Rui
Mohd123 is offline   Reply With Quote

Old   February 8, 2013, 06:28
Default
  #5
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,756
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by RSilva View Post
Thank you for your reply Mohd123,

Before refining I get to about 10^-3 residual (standard for COMSOL) and after refining the value is about 10^-2.

Could it be that the boundary layer mesh is to fine and causing numerical diffusion?

Best Regards,

Rui
Hi,
for any consistent and stable discretization, in no way a grid refinement can cause an increasing in the numerical diffusion! Try check your iteration parameters
FMDenaro is offline   Reply With Quote

Reply

Tags
boundary layer mesh, k-epsilon turbulence, low reynolds

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
An error has occurred in cfx5solve: volo87 CFX 5 June 14, 2013 18:44
Validating OF, turbulent flow over flat plate Thilo OpenFOAM Verification & Validation 0 July 3, 2012 06:29
Turbulent viscosity ratio limited to 1.10^5 in boundary layer ingestion loicflouriot FLUENT 0 May 27, 2012 08:31
Boundary Layer roughness/ low reynolds wall treatment Luigi_ STAR-CCM+ 1 March 14, 2012 09:40
errors Fahad Main CFD Forum 0 March 23, 2004 14:20


All times are GMT -4. The time now is 22:35.