K-omega SST Wall functions

ajmwtt · March 20, 2019, 05:57

I have noticed when selecting K-omega SST as a turbulence model that there is no option to select wall functions whereas when selecting K-epsilon there is? Is this because there is no wall functions used in K-omega SST or just because Ansys doesn't allow the use of them for this model? Additionally, what should the Y+ range be for K-omega SST, is there are no wall functions then it should be 1-5, is that correct?

Thanks in advance

LuckyTran · March 20, 2019, 09:23

There's only one wall function for the omega equation so there are no options. You get what you get. This wall function is rather crappy though because...

k-w (SST or not) is meant to be integrated all the way to the wall and yes you should be using it for low y+. If you are using a super high y+ grid, then go with regular k-epsilon.

josy · March 25, 2019, 10:36

i used the SST K Omega model to solve my simulation i obtained eddy viscosity but i need the molecular viscosity. how i can do this conversion from eddy viscosity to molecular viscosity
thanks

LuckyTran · March 25, 2019, 10:54

Quote:

Originally Posted by josy

i used the SST K Omega model to solve my simulation i obtained eddy viscosity but i need the molecular viscosity. how i can do this conversion from eddy viscosity to molecular viscosity
thanks

Don't hijack other people's threads for a different discussion!

There is no conversion. They are unrelated. Eddy viscosity is a flow property related to turbulence. Molecular viscosity is a material property which is readily available. If you got the eddy viscosity you can also find the molecular viscosity.

josy · March 25, 2019, 11:46

Thank you LuckyTran For your answers.
But how i can reach the molecular viscosity?

LuckyTran · March 25, 2019, 13:04

How did you get to eddy viscosity?

If you're in the GUI and trying to make a contour or monitor or anything, molecular viscosity is grouped in properties.

josy · March 25, 2019, 14:00

To have the eddy viscosity i run the simulation and go in the part result of ansys fluent and choice calculation --> areaAve --> Eddy viscosity --> Apply.
I didn't habe the molecular viscosity a Variable(result)to choice
So i though that i can take the Eddy viscosity and convert it.
Did you have any possibility ? PLEASE

LuckyTran · March 26, 2019, 08:54

I don't know what to tell you except it's right there. It's not magic.

Maybe you can explain what you are (not) doing.

josy · March 26, 2019, 09:51

after initialisation i have this error

"Error: domain-var-value: undefined variable
Error Object: pb/sg-pb-dqmom?"

what is it mean please

LuckyTran · March 26, 2019, 10:39

Make your own thread! This is no longer a discussion of k-w SST nor wall functions. I am not answering any more of your queries in this thread unless it's related to one of those two topics. You keep coming up with new problems.

March 20, 2019, 05:57	K-omega SST Wall functions	#1
ajmwtt New Member Join Date: Mar 2019 Posts: 1 Rep Power: 0	I have noticed when selecting K-omega SST as a turbulence model that there is no option to select wall functions whereas when selecting K-epsilon there is? Is this because there is no wall functions used in K-omega SST or just because Ansys doesn't allow the use of them for this model? Additionally, what should the Y+ range be for K-omega SST, is there are no wall functions then it should be 1-5, is that correct? Thanks in advance

March 20, 2019, 09:23		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,753 Rep Power: 66	There's only one wall function for the omega equation so there are no options. You get what you get. This wall function is rather crappy though because... k-w (SST or not) is meant to be integrated all the way to the wall and yes you should be using it for low y+. If you are using a super high y+ grid, then go with regular k-epsilon. robboflea and racing_student like this.

March 25, 2019, 10:36	eddy viscosity	#3
josy New Member josymany21@yahoo.fr Join Date: Mar 2019 Posts: 5 Rep Power: 7	i used the SST K Omega model to solve my simulation i obtained eddy viscosity but i need the molecular viscosity. how i can do this conversion from eddy viscosity to molecular viscosity thanks

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March 25, 2019, 11:46		#5
josy New Member josymany21@yahoo.fr Join Date: Mar 2019 Posts: 5 Rep Power: 7	Thank you LuckyTran For your answers. But how i can reach the molecular viscosity?

March 25, 2019, 13:04		#6
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,753 Rep Power: 66	How did you get to eddy viscosity? If you're in the GUI and trying to make a contour or monitor or anything, molecular viscosity is grouped in properties.

March 25, 2019, 14:00		#7
josy New Member josymany21@yahoo.fr Join Date: Mar 2019 Posts: 5 Rep Power: 7	To have the eddy viscosity i run the simulation and go in the part result of ansys fluent and choice calculation --> areaAve --> Eddy viscosity --> Apply. I didn't habe the molecular viscosity a Variable(result)to choice So i though that i can take the Eddy viscosity and convert it. Did you have any possibility ? PLEASE

March 26, 2019, 09:51		#9
josy New Member josymany21@yahoo.fr Join Date: Mar 2019 Posts: 5 Rep Power: 7	after initialisation i have this error "Error: domain-var-value: undefined variable Error Object: pb/sg-pb-dqmom?" what is it mean please

March 26, 2019, 10:39		#10
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,753 Rep Power: 66	Make your own thread! This is no longer a discussion of k-w SST nor wall functions. I am not answering any more of your queries in this thread unless it's related to one of those two topics. You keep coming up with new problems.