CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > Siemens > STAR-CCM+

convergence issue flow around circular cylinder

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

View Poll Results: what kind of recomended action?
refine mesh 0 0%
lower time step 0 0%
increase inner iteration count 2 100.00%
go home kid you have no idea what you're doing 0 0%
Multiple Choice Poll. Voters: 2. You may not vote on this poll

Like Tree1Likes
  • 1 Post By SB123

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 9, 2014, 10:15
Default convergence issue flow around circular cylinder
  #1
Member
 
Join Date: Mar 2013
Posts: 42
Rep Power: 13
SB123 is on a distinguished road
I'm modeling flow about a circular cylinder in the critical to super critical region of flow. and i'm trying to do a mesh dependency study.
so i've been reading around about convergence and i know there's no set definition. some say monitor until residuals drop below certain value (0.001 or 0.000001 etc.) or go flat, that depends on the problem. others say residuals mean nothing and say put all stock into monitoring physical attributes of the flow ie lift/drag. so i've done both and i have a question about that now. and i'm monitoring my residuals which go flat but at a high level (ie high error between iteration calculation <- am i right?) so if my error is so high i've reduced my mesh to reduce it but i'm up to a 0.5 million cells currently

the picutres above (all but last) mesh has 44k cells, but i've gone up t0 0.5 million cells and had pretty much the same response. the time step is @ 0.001s which is <1% of the expected shedding frequency (i believe) . the inner iterations are at 5/timestep.

here are my C_d values
cell count Re=5e5 Re=1.5e6 Re=3e6
49,000 0.953736 0.8779298 0.75971
130,000 0.894744 0.7971384 0.666037
500,000 0.819921 0.7164173 0.695576

should i be worrying about CFL number here? should i just keep reducing my mesh size? i feel like i should be able to run a simulation as simple as this on a laptop, but if i keep growing this mesh then i fear i may not be able to. is there something simple that i'm missing?

Last edited by SB123; November 10, 2014 at 18:55.
SB123 is offline   Reply With Quote

Old   December 13, 2014, 16:18
Default
  #2
Member
 
Join Date: Mar 2013
Posts: 42
Rep Power: 13
SB123 is on a distinguished road
i've since figured that i needed more inner iterations per time step. currently using flexible up to 50/timestep and getting much better convergence. this solved my high residual issue
bojueyang likes this.
SB123 is offline   Reply With Quote

Reply

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
2D flow around a circular cylinder case with interFoam solver shuoxue OpenFOAM Running, Solving & CFD 2 January 14, 2020 14:23
2D flow around a circular cylinder case with interFoam solver shuoxue OpenFOAM Running, Solving & CFD 0 August 31, 2013 06:04
FLUENT, flow past a circular cylinder Paul Reichl Main CFD Forum 16 December 8, 2012 16:21
Flow around a sphere and a circular cylinder Francis Main CFD Forum 0 September 29, 2008 06:16
3D Flow over a circular cylinder Srinivas FLUENT 3 March 15, 2005 20:57


All times are GMT -4. The time now is 11:13.