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

low Re (30-170) Karman vortex street

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 16, 2007, 14:27
Default low Re (30-170) Karman vortex street
  #1
Sponi
Guest
 
Posts: n/a
Hello to everybody. I am trying to simulate Karman vortex series at low Re number, 30 up to 170. From literature is known critical Re = 47 +- 0.5, whereat is boundary layer periodic break away from cylinder wall and phenomenon Karman vortexreet is created. My 2D case is seting up like this: - isothermal simulation - fluid material is an air - cylinder diameter D=1.07 mm - inspection area has rectangular shape with this dimension: 100*D in front of a cylinder, 150*D below, and width is 200*D. Selectin of this dimensions is coming out from literature, where is noted minimal distance from cylinder to boundary for simulation low Re, 60D to 100D. - height of first cell is 0.001 mm (centroid is at 5e-04 m) - size of grid is about 45 000 (grid independcy was checked up to 0.5 mil cells)

Results from simulation is very good with experimental data in range of Re=60 to 170. Max. relative deviation is 1.2%. I never get simulation with vortex shedding for Re<60.

Solver Settings: - in first step is steady simulation done: 150 iteration 1st order and then Second Order for pressure, QUICK from Momentum and SIMPLEC for press-veloc. coupling. When I get periodic lift and drag coefficinet, then I start unsteady simulation with 2nd order time discetazion and same discret. scheme from steady simulation for press and momentum (2nd order press., QUICK momomentum) - during unsteady simulation are checking all residuals (x,y-veloc and continuity). I set-up 0.5e-04 for continuity - unsteady simulation is convergency in every time step with 3-5 iteration per time step. - legth of time step is derived from known Strouhal number, where is frequency f. I can determine period T=1/f. After that time step is Dt=T/60 (or 6 degree in angle interpretation)

Trouble: How I said, result for Re=60 and higher are very well with present experimental data. But I never achieved vortex shedding for Re<60. Even if sctructure grid is fine enough 45e+03 to 500e+03 cells. Neither Third Order MUSCL for momentum nor shorter time step (Dt=T/120, Dt=T/360) didn't help.

Question: Is there any way, how could I bring near to critical Re=47+-0.5? Thanks a lot for your suggestions! -David Sponiar, Prague, Czech Rep.-

  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
karman vortex street help please SSeth STAR-CCM+ 7 January 10, 2011 12:31
Karman vortex street ??? anisa FLUENT 1 May 5, 2005 13:04
Multicomponent fluid Andrea CFX 2 October 11, 2004 05:12
Karman vortex street Zhipeng FLUENT 5 June 24, 2002 11:00
Kármán vortex street in cavitating flow behind bodies in the cavitation tunnel L. Könözsy Main CFD Forum 0 April 17, 2000 13:16


All times are GMT -4. The time now is 07:07.