# Help on accessing volume fraction in mixture model

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 April 20, 2009, 14:14 Help on accessing volume fraction in mixture model #1 New Member   Aditya Chunekar Join Date: Mar 2009 Posts: 18 Rep Power: 8 I am writing a UDF that involves volume fraction for Unsteady RANS simulation with cavitation model turned on. I define a user defined memory variable and use the following snippet of code to access it. DEFINE_EXECUTE_AT_END(udf_name) { ........ /* All the definitions */ d=Get_Domain(3); /* Vapor Phase domain thread_loop_c(t,d) { begin_c_loop(c,t) { C_UDMI(c,t,1)=C_VOF(c,t); } } end_c_loop(c,t) } } (This is just to show how I access C_VOF.. I perform some other operations on it) I get the value of C_UDMI(c,t,1) as 0 everywhere when the volume fraction of phase 2 varies from 0 to 0.4. Can someone please help me on the same. Thanks

 April 20, 2009, 15:03 #2 New Member   Aditya Chunekar Join Date: Mar 2009 Posts: 18 Rep Power: 8 I think the problem is with C_UDMI, since I can modify the values of volume fraction using C_VOF variable. I guess the problem is def of C_UDMI for the mixture domain. Is there any way to define a C_UDMI for a phase ?

 April 20, 2009, 15:57 #3 New Member   Aditya Chunekar Join Date: Mar 2009 Posts: 18 Rep Power: 8 I found something strange. The initial contours of void fraction show the values in the range of 0 to 0.4 thread_loop_c(t,d) { begin_c_loop(c,t) { if(index==1) { C_UDMI(c,t,1)=C_VOF(c,t); /* >>>>> Over here C_VOF(c,t) is approx 0 C_VOF(c,t) = 1 ; /** Some arbit modification } } end_c_loop(c,t) } Now if I check out the contours of volume fraction for phase 2 it shows 1 everywhere... ! So somehow C_VOF does not get the initial data on void fraction.... Am i doing something obviuosly wrong ? pls let me know ..

 April 21, 2009, 11:30 #4 New Member   Join Date: Apr 2009 Posts: 4 Rep Power: 8 hello aditya, i hope you are aware that there are some special multiphase macros avaialble. i am sure your required domain is not passing with get_domain. can you please try once with domain_sub_domain.... you can find more details on this in UDF manual. i hope fluent support can help you on this.

 April 21, 2009, 13:02 #5 New Member   Aditya Chunekar Join Date: Mar 2009 Posts: 18 Rep Power: 8 Thanks, But the fact that I am able to modify the value of volume fraction of phase 2 through the same loop means that I am passing the phase domain to the loop. Somehow the current values are not being accessed. I have contacted Fluent support.. Hope they help me on it

 April 22, 2009, 11:42 #6 New Member   Join Date: Apr 2009 Posts: 4 Rep Power: 8 i hope domain_id =3 what you have used is picked from define->phases, for vapour phase. since domain id are not necessarily sequential. if this is correct, would you mind sharing sample case with me. i can help you on that. i have tested at my end it works fine.

 April 23, 2009, 13:30 #7 New Member   Aditya Chunekar Join Date: Mar 2009 Posts: 18 Rep Power: 8 cfdpinku, Cannot upload the file over here. Exeeds the file limit Can you please pm me your email ed ? The total size is around 4 mb Aditya

 September 4, 2009, 06:21 #8 New Member   asif nazir Join Date: Aug 2009 Posts: 3 Rep Power: 7 hi u should go into subdomain thread then it work

 September 4, 2009, 06:22 #9 New Member   asif nazir Join Date: Aug 2009 Posts: 3 Rep Power: 7 THREAD_SUB_THREAD look this macro from the manual

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