Imporatnt questions

happy · March 4, 2012, 02:23

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

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

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

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

Quote:

Originally Posted by ghorrocks

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

happy · March 5, 2012, 05:36

It looks no one know

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, 01:30

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

ghorrocks · March 12, 2012, 04:24

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.

March 4, 2012, 02:23	Imporatnt questions	#1
happy Senior Member Safia Join Date: Oct 2010 Location: Australia Posts: 161 Rep Power: 15	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

March 4, 2012, 05:06	share us youe knowledge	#4
happy Senior Member Safia Join Date: Oct 2010 Location: Australia Posts: 161 Rep Power: 15	Hi Glenn By the way, you did not answer my question into your first input??tell me if you are still confusing Regards

March 5, 2012, 05:36	no one know	#7
happy Senior Member Safia Join Date: Oct 2010 Location: Australia Posts: 161 Rep Power: 15	It looks no one know it is easy w.r.t Glenn and some guests. I want to make sure help me please.

March 5, 2012, 18:03		#9
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,167 Rep Power: 23	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.

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March 4, 2012, 04:01		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	K-epsilon turbulence model is the default. Where are you saying you tick eddy diffusivity?

March 4, 2012, 16:38		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	The default when you set up a fluid domain is that it has the k-e turbulence model applied.

March 5, 2012, 05:43		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	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?

March 12, 2012, 01:30		#10
happy Senior Member Safia Join Date: Oct 2010 Location: Australia Posts: 161 Rep Power: 15	hi Erik you are compeletly understand me. yes, that what i meant. regards

March 12, 2012, 04:24		#11
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	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.