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

Strouhal number for sphere and high Re

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 13, 2016, 05:56
Default Strouhal number for sphere and high Re
  #1
New Member
 
Join Date: Oct 2016
Posts: 2
Rep Power: 0
Freddeflopp is on a distinguished road
Dear members and experts,
I need to roughly approximate the strouhal-number for a sphere in free flow.
The free velocity of surrounding air is 10-45 m/s, e.g. a high Re above 1e6

The literature and works I've found mainly treats much lower Re

Looking for St number for cylinders does not seem to be appropriate, since I believe the number should be considerably higher for a sphere in this Re region.

What is a good approximation of St in this region?

Any help is much appreciated

best regards,
Fred
Freddeflopp is offline   Reply With Quote

Old   October 18, 2016, 12:34
Default
  #2
Member
 
Join Date: May 2014
Posts: 30
Rep Power: 12
mome is on a distinguished road
Hi, I'm not very knowledgeable about this, but I thought there is an upper critical Reynolds number of about ~3e5 for vortex shedding of spheres no? Could be wrong but what if you don't have large scale oscillations at all? I'm sure you can find plenty on it..
mome is offline   Reply With Quote

Old   October 19, 2016, 18:18
Default
  #3
New Member
 
Join Date: Oct 2016
Posts: 2
Rep Power: 0
Freddeflopp is on a distinguished road
Thanks for the reply!

Yes, you are 100% correct. However, there seems to be a re-establishment of the turbulent vortex street when Re get higher than 3.5e6 (for cylinders) according to lectures and some researchers. see for example slide 5 in the link below (they refer to J. Lienhard):

web.mit.edu/13.42/VIV_2004.ppt

However, I cant find any result concerning spheres. In this case low frequencies were unwanted, so I used a cylinder worst case approximation with St=0.2 and got low, but acceptable frequencies.

I would be interesting to know if the re-establishment only is valid for cylinders.
Freddeflopp is offline   Reply With Quote

Old   October 20, 2016, 08:41
Default
  #4
Member
 
Join Date: May 2014
Posts: 30
Rep Power: 12
mome is on a distinguished road
yeah I recall these coherent structures around cylinders, don't know if something like that exists for spheres and after a 5 minute google I agree that there is not so much work at Re>10e6..
I have the impression there are no observations of that phenomenon though. I found info that beyond 3.7e5 the estabished vortex pair is steady. And a report that shows peaks in the spectrum at up to 1.2e6 attributes this to a vibration in their frame

maybe you can find more! Good luck
Would be interesting to know..
M.
mome is offline   Reply With Quote

Reply

Tags
high reynolds number, sphere, strouhal number


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
TwoPhaseEulerFoam high courant number mwaqas OpenFOAM Running, Solving & CFD 11 July 11, 2017 15:19
multiphaseEulerFoam high Courant number Frenk_T OpenFOAM 5 November 24, 2016 04:23
Circular cylinder vortex shedding/strouhal number too high li0012in CFX 7 April 28, 2016 21:56
Visualizing mesh regions with high courant number? Endel OpenFOAM 2 August 20, 2013 04:57
Multicomponent fluid Andrea CFX 2 October 11, 2004 06:12


All times are GMT -4. The time now is 22:00.