CFD Online URL
[Sponsors]
Home > Forums > Main CFD Forum

Increasing instability for flow around as cylinder.

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 12, 2013, 05:35
Default
  #21
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 1,288
Rep Power: 17
FMDenaro will become famous soon enough
In my opinion, the grid is extended enough from the cylinder, perhaps I don't understand the requirement to use an O-grid ...
First, the instability should appear also for laminar flows, therefore I would try the solver without any tubrulence modelling, then I see only 600 time-steps that can be not sufficient to develop instability. An acceleration of the onset of the instability can be obtained by prescribing small fluctuations in the initial condition.
Finally, owing to the particular shape of the grid, I would take attention to the outflow conditions
FMDenaro is offline   Reply With Quote

Old   February 12, 2013, 06:34
Default
  #22
Senior Member
 
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 355
Rep Power: 9
arjun is on a distinguished road
Quote:
Originally Posted by RodriguezFatz View Post
But do you think his domain looks like it is too small compared to the radius?

can't really say. Because with iNavier and old versions of fluent like fluent 6.3 i could get vortex shedding even when boundaries were close.

I was just sharing my experience with such problem how it went away. So it is worth trying. Personally I do think with finite volume codes like fluent starccm he should have got this vortex shedding without much of hassle.
arjun is offline   Reply With Quote

Old   February 12, 2013, 06:35
Default
  #23
Senior Member
 
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 355
Rep Power: 9
arjun is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
In my opinion, the grid is extended enough from the cylinder, perhaps I don't understand the requirement to use an O-grid ...
First, the instability should appear also for laminar flows, therefore I would try the solver without any tubrulence modelling, then I see only 600 time-steps that can be not sufficient to develop instability. An acceleration of the onset of the instability can be obtained by prescribing small fluctuations in the initial condition.
Finally, owing to the particular shape of the grid, I would take attention to the outflow conditions

that may very well be the issue here. It usually requires much larger number of steps to get.
arjun is offline   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
benchmark: flow over a circular cylinder goodegg Main CFD Forum 12 January 22, 2013 12:47
Incorrect Drag and Drag Coefficient for flow over a cylinder ozzythewise Main CFD Forum 8 June 13, 2012 07:24
Specifying boundary faces failes in blockMesh blaise OpenFOAM Meshing & Mesh Conversion 0 May 10, 2010 04:56
rotating cylinder using sliding mesh Tim Daly FLUENT 1 November 10, 2008 00:02
flow over a cylinder urgent! kevin FLUENT 7 June 8, 2006 02:19


All times are GMT -4. The time now is 13:53.