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

Dear Astrid!!!

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

Reply
 
LinkBack Thread Tools Display Modes
Old   April 14, 2002, 17:00
Default Re: Dear Astrid!!!
  #21
Astrid
Guest
 
Posts: n/a
- What is your Reynolds number?

- Do you work on Sunday? Or do you work in Japan where it is already Monday. Where is .se?

Astrid
  Reply With Quote

Old   April 14, 2002, 17:06
Default Re: Dear Astrid!!!
  #22
Dimitris
Guest
 
Posts: n/a
*LOL* No....I'm doing my master thesis and my supervisor is like a slave master.....he he he....I have to work day and night... .se is Sweden....I'm in Stockholm at the Royal institute of technology...and you? My Re is 2.0417E+06...
  Reply With Quote

Old   April 14, 2002, 17:16
Default Re: Dear Astrid!!!
  #23
Astrid
Guest
 
Posts: n/a
- I'm in The Netherlands. I am just doing this for the lol, on a Sunday after-afternoon

- Quite high Reynolds number. Don't you expect any 3D-effects? Unsteady flow behavior or flow separation? Just curious.

Astrid
  Reply With Quote

Old   April 14, 2002, 17:24
Default Re: Dear Astrid!!!
  #24
Dimitris
Guest
 
Posts: n/a
You seem to know a great deal about CFD though....I'm just an novice....but I'm trying... Well...I guess I have a some 3D effects but considering what I'm solving from my point of view those are negligble... Do you work with CFD?
  Reply With Quote

Old   April 14, 2002, 22:24
Default Re: Dear Astrid!!!
  #25
Neale
Guest
 
Posts: n/a
Dimitris,

I think you need to spend a bit of time diagnosing why k and epsilon residuals are stalling. If that is the case then I would be suprised if fluids residuals are not stalling at some point. Since you are simulating flow around a cylinder at fairly high Reynolds number you might expect this flow to be transient, i.e. vortex shedding.

If you want to "smooth" this out so that you can average out the vortex shedding I suspect that you might have to play with the inlet turbulence levels. Do you have data for this from your experiments? Two things to check are whether or not the turbulence is decaying within a few cells downstream of your inlet, and also what does the turbulent viscosity field look like? Or more importantly, the turbulent viscosity ratio, mu_T/mu. If mu/mu_T is mostly 1 throughout your domain (or in the area immediately surrounding the cylinder) then the turbulence model is basically doing nothing for you in these flow regions. Hence, you may need to play with the inlet turbulence levels to get things "diffusive" enough to stablise the solution.

One other issue with these flows around cylinders is domain confinement. If it is over confined then you could also run into problems. i.e. you will get the wrong shedding frequency because the shedding wavelength can adopt to the channel width. Does your geometry exactly match your experimental setup, or is it a small cut out? This might not be important for you if the shedding frequency does not matter.

Neale.

  Reply With Quote

Old   April 15, 2002, 16:56
Default Re: Dear Astrid!!!
  #26
Astrid
Guest
 
Posts: n/a
Dimitris,

please read the latest posting of Neale very carefully. As vortex shedding might be important, you should consider switching to a full 3D description. Then use the SST model which is capable of calculating a decent Cd coefficient and shedding frequency. Then you have to fully integrate everything to the wall. However......, for the flow around a cilinder I have only tested SST up to Re = 1e5. So, this differs from your case.

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
Dear Dr. Mike Baheri Phoenics 0 September 24, 2007 07:03
Dear Mike, ... james Phoenics 1 August 30, 2007 05:59
Dear Jonas, it seems to me We have a small problem Michail CFD-Wiki 3 December 10, 2005 18:43
i want to find my dear friend ... kevin FLUENT 0 February 28, 2002 21:15
Find a my dear friend ..... kevin FLUENT 0 February 25, 2002 22:28


All times are GMT -4. The time now is 17:17.