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

Imporatnt questions

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

Like Tree1Likes
  • 1 Post By evcelica

Reply
 
LinkBack Thread Tools Display Modes
Old   March 4, 2012, 03:23
Default Imporatnt questions
  #1
Senior Member
 
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 6
happy is on a distinguished road
Hi there,,,
I have question about the way of using the models into CFX.
For example, if I need to use K-epcilon turbulent model, I'm always thinking that if I did not tick any square in the path (Domain:.../Fluidmodel/any parameter.....) mean that the program will use the default setting? is this right).
As well as, for the same model and regarding the eddy diffusivety, if I did not tick it, the program will calculated and if I tick it, it means that I should insert a value. is this either correct?
Please, answer my question as soon as possible where I misrecognise these things.
Regards
happy is offline   Reply With Quote

Old   March 4, 2012, 05:01
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,951
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
K-epsilon turbulence model is the default.

Where are you saying you tick eddy diffusivity?
ghorrocks is offline   Reply With Quote

Old   March 4, 2012, 06:01
Default
  #3
Senior Member
 
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 6
happy is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post
K-epsilon turbulence model is the default.

Where are you saying you tick eddy diffusivity?
I mean into setup there are many parameters I should set to make the model work. I did not meant the K-E only, but The same thing is thrugh the models.
happy is offline   Reply With Quote

Old   March 4, 2012, 06:06
Question share us youe knowledge
  #4
Senior Member
 
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 6
happy is on a distinguished road
Hi Glenn
By the way, you did not answer my question into your first input??tell me if you are still confusing
Regards
happy is offline   Reply With Quote

Old   March 4, 2012, 17:38
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,951
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
The default when you set up a fluid domain is that it has the k-e turbulence model applied.
ghorrocks is offline   Reply With Quote

Old   March 5, 2012, 02:05
Default still need answers
  #6
Senior Member
 
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 6
happy is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post
K-epsilon turbulence model is the default.

Where are you saying you tick eddy diffusivity?
Can you plz see http://ifile.it/dne36a5 to know what i meant.
If you understand me, please answer my previous questions and next one,,,
Is is important to inter specific value for eddy viscosity. and if I did not tick it, will the progaram calculate it?
Regards

Last edited by happy; March 5, 2012 at 05:06.
happy is offline   Reply With Quote

Old   March 5, 2012, 06:36
Angry no one know
  #7
Senior Member
 
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 6
happy is on a distinguished road
It looks no one know
it is easy w.r.t Glenn and some guests.
I want to make sure help me please.
happy is offline   Reply With Quote

Old   March 5, 2012, 06:43
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,951
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
I do not use 3rd party download tools so have not seen your attachment. Please attach it to the forum.

I do not understand your previous question beyond what I have already said, you will have to write it more clearly.

Your question about entering eddy viscosity is vague - where are you entering this?
ghorrocks is offline   Reply With Quote

Old   March 5, 2012, 19:03
Default
  #9
Senior Member
 
Erik
Join Date: Feb 2011
Location: Earth (Land portion)
Posts: 487
Rep Power: 10
evcelica is on a distinguished road
I think he is saying where you can choose to enter a value for something or not, like when you can mark the checkbox that reads Turbulent Flux closure for heat transfer, then an option comes up to Turbulent Prandtl number, the box is already populated with 0.9.

Same thing with Buoyancy turbulence, you can check mark a box for turbulent schmidt number, which then allows you to input a value, which is already populated with 0.9.

He is asking are these already set to 0.9 even if you don't check the box, or if the program will just calculate a value if we don't check these boxes?

I'm under the impression they are 0.9 by default, because i did not see an equation for calculating them in the solver theory guide, though i may have missed it.
happy likes this.
evcelica is offline   Reply With Quote

Old   March 12, 2012, 02:30
Default
  #10
Senior Member
 
Safia
Join Date: Oct 2010
Location: Australia
Posts: 161
Rep Power: 6
happy is on a distinguished road
hi Erik
you are compeletly understand me.
yes, that what i meant.
regards
happy is offline   Reply With Quote

Old   March 12, 2012, 05:24
Default
  #11
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,951
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
The Schmidt number of 0.9 is one of several turbulence model constants. It is empirically tuned to match experimental data, it has not been theoretically derived. That is why it is called a turbulence MODEL, not a turbulence THEORY.
ghorrocks is offline   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
possible interview questions atturh Main CFD Forum 1 February 21, 2012 09:53
FSI problem , Help needed for my basic questions kmgraju CFX 1 July 29, 2011 00:04
NACA0012 Validation Case Questions ozzythewise Main CFD Forum 3 August 3, 2010 14:39
Questions about CFD Lebeau alexandre Main CFD Forum 1 April 6, 1999 14:23
turbulence modeling questions llowen Main CFD Forum 3 September 11, 1998 04:24


All times are GMT -4. The time now is 10:07.