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

Vortex shedding data

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 15, 2002, 04:31
Default Vortex shedding data
  #1
Jan Rusås
Guest
 
Posts: n/a
Hi All, I have been comparing the results from a CFX calculation of the flow around a tube with some data. I can not get satisfying results, It can be CFX (or me ) that is the problem, but the data I have is also not very good. Does anyone know any good simple testcase/testexample that I can acces online.

Thanks in advance Jan
  Reply With Quote

Old   October 15, 2002, 09:04
Default Re: Vortex shedding data
  #2
Jan Rusås
Guest
 
Posts: n/a
It was the data that was the problem, I have now solved another case with perfect match. Jan
  Reply With Quote

Old   October 15, 2002, 09:15
Default Re: Vortex shedding data
  #3
Bart Prast
Guest
 
Posts: n/a
Jan,

what settings did you use (turbulence model etc)? Did you use CFX 5?
  Reply With Quote

Old   October 15, 2002, 17:56
Default Re: Vortex shedding data
  #4
Astrid
Guest
 
Posts: n/a
Cd and Cf coefficients are well documented as well as Strouhal numbers/frequencies. Or do you require detailed velocity data?

Astrid
  Reply With Quote

Old   October 16, 2002, 03:07
Default Re: Vortex shedding data
  #5
Jan Rusås
Guest
 
Posts: n/a
I was using CFX4, now I am trying to solve it with CFX5 - hope I get the same result Jan
  Reply With Quote

Old   October 16, 2002, 03:09
Default Re: Vortex shedding data
  #6
Jan Rusås
Guest
 
Posts: n/a
Dear Astrid, I was just trying to get the same Strouhal number, which I failed for the first case I was looking at, but now it works fine. Regards Jan
  Reply With Quote

Old   October 18, 2002, 07:23
Default Re: Vortex shedding data
  #7
Astrid
Guest
 
Posts: n/a
For research puposes, we also perform this kind of simulations. Therefore three questions:

1) What is the Re-number of your problem? 2) Which turbulence model do you use in CFX 4 and 5? 3) Does heat transfer play any role in your problem?

Astrid
  Reply With Quote

Old   October 20, 2002, 12:34
Default Re: Vortex shedding data
  #8
Jan Rusås
Guest
 
Posts: n/a
Dear Astrid, Answer to you question. 1) Re = 100 2) Laminar in both codes 3) No I did predict the St # within 0.25% (in CFX4.4) so for this case I am satisfied.

The reson why I am doing this is that I have to investigate a real problem, where the flow is turbulent and with heat transfer to the pin. I just wanted to start easy and get a feeling of the problem. My largest problem is now to get used to CFX5 (((, I can not even get any transient flow in CFX5 for the same case at the moment. Odd there is only very few options in CFX5 for the transient flow (only the timestep nothing abouth the methode)
  Reply With Quote

Old   October 20, 2002, 18:14
Default Re: Vortex shedding data
  #9
Astrid
Guest
 
Posts: n/a
We have performed simulations at a wide range of Re-numbers. Our experience is that you require quite a lot of timesteps to obtain the required oscillations. Just give CFX 5 a bit more time....... )))

Astrid
  Reply With Quote

Old   October 21, 2002, 03:32
Default Re: Vortex shedding data
  #10
Jan Rusås
Guest
 
Posts: n/a
In CFX4 the oscillations started after 40sek and became periodic. I have now done the same simulation in CFX5 and I have calculated to the time 120sek and nothing is happening (. I do think that should be sufficient, I am looking into if I have missed something. Would you share your experience with CFX5 on this type of problem Astrid?

-How important is the number of iterations in each timestep, and what is sufficient. What should the convergence level be? Any difference in single or double precision? -For turbulent problems, any good hints, is the scalable wall model the best? -Is the any problems when heat transfer is involved? Regards Jan

  Reply With Quote

Old   October 21, 2002, 10:14
Default Re: Vortex shedding data
  #11
Neale
Guest
 
Posts: n/a
Jan,

Are you running second order transient? You can't turn this on from the GUI. You have to do it manually in the solver CCL file. Extract it using cfx5cmds, add the following to the SOLVER CONTROL singleton:

TRANSIENT SCHEME: Option = Second Order Backward Euler END

The numerics in CFX-4/5 completely differ so you might need to perturb the flow a bit at the beginning in CFX-5 to get the vortex shedding going. Try a transient pulse on the inlet velocity at the beginning of the run.

I would suggest that you also ensure that you are running a small enough timestep in CFX-5 that guarantees that you get convergence to your target residuals within each timestep. If you don't make sure that this is happening then your results will likely be nonsense.

Hopefully this helps you out a bit.

Neale.
  Reply With Quote

Old   November 5, 2002, 17:09
Default Re: Vortex shedding data
  #12
Astrid
Guest
 
Posts: n/a
Jan,

Do you read your e-mail.....

Astrid
  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
K-Epsilon for Vortex Shedding Sham FLUENT 30 July 10, 2015 21:13
Transiet Animation - vortex shedding derz CFX 5 May 10, 2010 09:21
Vortex shedding behind cylider in cross flow Muthu FLUENT 0 March 6, 2006 11:29
How to update polyPatchbs localPoints liu OpenFOAM Running, Solving & CFD 6 December 30, 2005 18:27
basic vortex shedding john Main CFD Forum 4 November 6, 2000 14:23


All times are GMT -4. The time now is 19:53.