User-defined k

gina · October 17, 2009, 13:22

Dear all,
I want to use UDF to modify the kinetic energy (k) field in the locations where the y plus value is less than 20.

is there anyone who can help me?
thanks

tstorm · October 17, 2009, 19:39

You can define a new source equation (using DEFINE_SOURCE), and inside that source add an if statement to take care of the y+<20 part. Then you'll hook that source equation to the k equation (DEFINE - BOUNDARY CONDITIONS - FLUID).

I'd be happy to help you along if you have more specific questions.

gina · October 23, 2009, 15:12

thank you very much to have answer for me...
I have use a udf with define_adjust, is that not correct!

tstorm · October 23, 2009, 19:05

Yes, you can use an define_adjust as well, there are several ways to approach your problem.
You can use define_adjust to adjust the k value.
Or, you can use define_source to define a NEW k value, and set your new value to FLUENT's k.

gina · October 24, 2009, 17:13

Ok well, please if i need to use define_source and when i will to hook my source equation in DEFINE - BOUNDARY CONDITIONS - FLUID in this panel what I must do?
thanks

t.krishnamohan · October 26, 2009, 08:42

Hi,
DEFINE_WALL_FUNCTIONS should be used for specifying user defined wall functions. Hope you are using k-epsilon model to define turbulence. Please go through the online doc for number of arguments for this function.
You cannot use DEFINE_SOURCE/ DEFINE_ADJUST for specifying user defined wall functions.
Regards,

October 17, 2009, 13:22	User-defined k	#1
gina Member gina Join Date: Apr 2009 Posts: 56 Rep Power: 17	Dear all, I want to use UDF to modify the kinetic energy (k) field in the locations where the y plus value is less than 20. is there anyone who can help me? thanks

October 24, 2009, 17:13	define_source	#5
gina Member gina Join Date: Apr 2009 Posts: 56 Rep Power: 17	Ok well, please if i need to use define_source and when i will to hook my source equation in DEFINE - BOUNDARY CONDITIONS - FLUID in this panel what I must do? thanks

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October 17, 2009, 19:39		#2
tstorm Member Join Date: Apr 2009 Posts: 78 Rep Power: 17	You can define a new source equation (using DEFINE_SOURCE), and inside that source add an if statement to take care of the y+<20 part. Then you'll hook that source equation to the k equation (DEFINE - BOUNDARY CONDITIONS - FLUID). I'd be happy to help you along if you have more specific questions.

October 23, 2009, 15:12		#3
gina Member gina Join Date: Apr 2009 Posts: 56 Rep Power: 17	thank you very much to have answer for me... I have use a udf with define_adjust, is that not correct!

October 23, 2009, 19:05		#4
tstorm Member Join Date: Apr 2009 Posts: 78 Rep Power: 17	Yes, you can use an define_adjust as well, there are several ways to approach your problem. You can use define_adjust to adjust the k value. Or, you can use define_source to define a NEW k value, and set your new value to FLUENT's k.

October 26, 2009, 08:42		#6
t.krishnamohan Member Krishna Join Date: Oct 2009 Posts: 34 Rep Power: 17	Hi, DEFINE_WALL_FUNCTIONS should be used for specifying user defined wall functions. Hope you are using k-epsilon model to define turbulence. Please go through the online doc for number of arguments for this function. You cannot use DEFINE_SOURCE/ DEFINE_ADJUST for specifying user defined wall functions. Regards,