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-   -   Imporatnt questions (http://www.cfd-online.com/Forums/cfx/98136-imporatnt-questions.html)

happy March 4, 2012 02:23

Imporatnt questions
 
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:o these things.
Regards

ghorrocks March 4, 2012 04:01

K-epsilon turbulence model is the default.

Where are you saying you tick eddy diffusivity?

happy March 4, 2012 05:01

Quote:

Originally Posted by ghorrocks (Post 347516)
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 March 4, 2012 05:06

share us youe knowledge
 
Hi Glenn
By the way, you did not answer my question into your first input??tell me if you are still confusing
Regards

ghorrocks March 4, 2012 16:38

The default when you set up a fluid domain is that it has the k-e turbulence model applied.

happy March 5, 2012 01:05

still need answers
 
Quote:

Originally Posted by ghorrocks (Post 347516)
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:confused:?
Regards

happy March 5, 2012 05:36

no one know
 
It looks no one know:eek:
it is easy w.r.t Glenn and some guests.
I want to make sure help me please.

ghorrocks March 5, 2012 05:43

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?

evcelica March 5, 2012 18:03

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 March 12, 2012 02:30

hi Erik
you are compeletly understand me.
yes, that what i meant.
regards

ghorrocks March 12, 2012 05:24

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.


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