How to write UDF

esha · February 23, 2020, 00:33

Hi everyone,
I am new to CFD. I am unable to understand coding written for ANSYS Fluent.
I know C language but kindly anyone ca tell me what is equation written in following code. What is UDSI and when one can use G(c,t). Thank you! Or highr appreciable if provide some helping material. As I have udf manual of ANSYS but it is so confusing I do not know how to use that?

source2 = eps*mu/tao/pow((1.-(C_UDSI(c,t,0)+C_UDSI(c,t,1))/L/L),2.0)*((1.-(C_UDSI(c,t,0)+C_UDSI(c,t,1))/L/L)*(C_UDSI_G(c,t,0)[0]+C_UDSI_G(c,t,2)[1]));
source2 = source2+eps*mu/tao/pow((1.-(C_UDSI(c,t,0)+C_UDSI(c,t,1))/L/L),2.0)*(C_UDSI(c,t,0)*(C_UDSI_G(c,t,0)[0]+C_UDSI_G(c,t,1)[0])+C_UDSI(c,t,2)*(C_UDSI_G(c,t,0)[1]+C_UDSI_G(c,t,1)[1]))/L/L;
dS[eqn] = 0.;

Светлана · February 23, 2020, 20:03

Hi esha

This is only two lines from the UDF. Can you please post the complete function?

Regards,
Svetlana

LuckyTran · February 24, 2020, 09:46

C_UDSI(c,t,i) is for accessing cell values for user-defined scalars
C_UDSI_G returns the gradient of the scalar

February 23, 2020, 00:33	How to write UDF	#1
esha Member Join Date: Aug 2018 Posts: 85 Rep Power: 7	Hi everyone, I am new to CFD. I am unable to understand coding written for ANSYS Fluent. I know C language but kindly anyone ca tell me what is equation written in following code. What is UDSI and when one can use G(c,t). Thank you! Or highr appreciable if provide some helping material. As I have udf manual of ANSYS but it is so confusing I do not know how to use that? source2 = epsmu/tao/pow((1.-(C_UDSI(c,t,0)+C_UDSI(c,t,1))/L/L),2.0)((1.-(C_UDSI(c,t,0)+C_UDSI(c,t,1))/L/L)(C_UDSI_G(c,t,0)[0]+C_UDSI_G(c,t,2)[1])); source2 = source2+epsmu/tao/pow((1.-(C_UDSI(c,t,0)+C_UDSI(c,t,1))/L/L),2.0)(C_UDSI(c,t,0)(C_UDSI_G(c,t,0)[0]+C_UDSI_G(c,t,1)[0])+C_UDSI(c,t,2)*(C_UDSI_G(c,t,0)[1]+C_UDSI_G(c,t,1)[1]))/L/L; dS[eqn] = 0.;

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February 23, 2020, 20:03		#2
Светлана Senior Member Svetlana Tkachenko Join Date: Oct 2013 Location: Australia, Sydney Posts: 407 Rep Power: 14	Hi esha This is only two lines from the UDF. Can you please post the complete function? Regards, Svetlana

February 24, 2020, 09:46		#3
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,675 Rep Power: 66	C_UDSI(c,t,i) is for accessing cell values for user-defined scalars C_UDSI_G returns the gradient of the scalar