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

Circular Couette Flow

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 12, 2008, 16:26
Default Circular Couette Flow
  #1
rockewan
Guest
 
Posts: n/a
Description: Circular Couette flow in 2D (laminar). Outer wall is rotating at various speed while inner wall is stationary. Since it is simulated in 2D, there is no end effect and thus the analytical solution is know as u(r)=C1*r+C2/r as shown here: http://en.wikipedia.org/wiki/Couette_flow On the radius direction, the velocity magnitude should increase almost linearly from 0 to the outer wall speed.

The Problem: Reasonable simulation results can be obtained for coarse mesh at low rotation speeds although it is noticeable that the velocity is lower at some cells or nodes. See the comparison below:

http://i217.photobucket.com/albums/c...ityProfile.jpg

However, when I was trying to refine the mesh, it doesn't converge at all, even if the results from coarse mesh is used as start value using "Interpolate Data". The residuals decrease to certain value (usually higher than 1E-4), and then increase gradually, it will stabilize at certain value eventually. One example is shown here:

http://i217.photobucket.com/albums/c...ualProfile.jpg

Although it is meaningless to discuss the unconverged results, I did notice that the pressure profile shows periodic trend like this (unlike the circular layer profile for converged ones):

http://i217.photobucket.com/albums/c...ureProfile.jpg

I tried several different geometry that has different r/R ratio, different mesh for every geometry, different rotation speed for every mesh (all cases are still within the laminar region). This problem tends to happen for large aspect ratio with finer mesh and higher rotation speed.

I tried to decrease the under-relaxation factor, it does not help. "Interpolate Data" does not help either. I also tried to use small rotation speed first, and then gradually increase the speed. It converged well initially, however, before it reaches my desired value, it will do the same thing at certain rotation speed.

Anyway, I am running out of ideas. Any suggestion is welcome.

If you want to try this simple case yourself, here are the parameters: r=0.039m; R=0.042m; outer wall rotation speed: 50rpm; inner wall rotation speed: 0

Gambit mesh parameters: Quad "Elements" and Map "Type" is used without "Smoother" 5 Layer Mesh (in radius direction) spacing: (0.042-0.039)/5=6E-4; 10 Layer Mesh: 3E-4; 20 Layer Mesh: 1.5E-4

It converges on the 5 and 10 layer meshes, but not on the 20 Layer mesh.
  Reply With Quote

Reply


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
couette flow thiagobaixo CFX 20 April 2, 2008 20:46
couette flow jbssastry FLUENT 2 March 6, 2007 08:58
Couette Flow Tex FLUENT 1 November 30, 2005 05:47
Couette Flow Vijay Patel Main CFD Forum 2 April 18, 2002 12:29
couette flow MURALI.K.P Main CFD Forum 3 June 9, 2000 13:03


All times are GMT -4. The time now is 10:50.