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-   -   Mach Number for post processing in flunet is not available.. (https://www.cfd-online.com/Forums/fluent-udf/224863-mach-number-post-processing-flunet-not-available.html)

rahulmule797@gmail.com March 5, 2020 23:48

Mach Number for post processing in flunet is not available..
 
Hello everyone,
i'm doing similation of SF6 circuit braker (Simplified nozzle geometry). i want to know the mach number along length of nozzle. I have varioation of Sonic velocity with respect to temp. with me. how to do it?

please help me out to resolve the issue....
i've tried using
1) Custom field function...
Mach Number= |V|/sqrt(1.095*146*temperature) /* Sonic velocity = Sqrt(gamma*R*temp.) */
but it overpredicts mach number value
2) write udf for sonic velocity using macro DEFINE_ADJUST(SONIC_VELOCITY,d) and assigned memory to it..
and then defined mach number in Custom field function as
Mach Number = |V|/ udm-17
this results in complete disaster.. it gives mach numer 7000-8000...
3)write udf for sonic velocity using macro DEFINE_EXECUTE_AT_END(SONIC_VELOCITY,d) and assigned memory to it..
and then defined mach number in UDF itself as
Mach_number = C_V(c,t)/C_UDMI(c,t,Ma)...
but still it is not working..:o

vinerm March 6, 2020 02:52

Mach Number
 
For post-processing within Fluent, Mach number is directly available under Velocity. Is it but showing up for you or do you want to define your own function for some other reason?

rahulmule797@gmail.com March 6, 2020 02:57

mach number is not available under velocity...
it is available when i select air as material, but i'm using user defined SF6 material

vinerm March 6, 2020 03:25

Speed of Sound
 
It is not about air but about density. Which model are you using for density of your material?

rahulmule797@gmail.com March 6, 2020 04:00

Quote:

Originally Posted by vinerm (Post 760660)
It is not about air but about density. Which model are you using for density of your material?

the density and other porperties are provided using UDF..
properties are varying with temperature and pressure..
temperature range 300K - 35000k
pressure range 1 bar- 10 bar

regards,
Rahul

vinerm March 6, 2020 04:26

Speed of Sound
 
Yes, with UDF applied to density, Mach number is not available since Sound of Speed may or may not have been provided via UDF.

If all the properties are varying, then you have to use those properties to define Mach number, i.e., \gamma as well as R have to be defined in terms of C_p and C_v. Whether you do it in CFF or UDF, the property variations have to be taken into account.

rahulmule797@gmail.com March 6, 2020 04:32

Quote:

Originally Posted by rahulmule797@gmail.com (Post 760638)
Hello everyone,
i'm doing similation of SF6 circuit braker (Simplified nozzle geometry). i want to know the mach number along length of nozzle. I have varioation of Sonic velocity with respect to temp. with me. how to do it?

please help me out to resolve the issue....
i've tried using
1) Custom field function...
Mach Number= |V|/sqrt(1.095*146*temperature) /* Sonic velocity = Sqrt(gamma*R*temp.) */
but it overpredicts mach number value
2) write udf for sonic velocity using macro DEFINE_ADJUST(SONIC_VELOCITY,d) and assigned memory to it..
and then defined mach number in Custom field function as
Mach Number = |V|/ udm-17
this results in complete disaster.. it gives mach numer 7000-8000...
3)write udf for sonic velocity using macro DEFINE_EXECUTE_AT_END(SONIC_VELOCITY,d) and assigned memory to it..
and then defined mach number in UDF itself as
Mach_number = C_V(c,t)/C_UDMI(c,t,Ma)...
but still it is not working..:o

i have sonic velocity data as function of presure and temperature...
and tried as ststed in post...

vinerm March 6, 2020 04:41

Udf
 
1. In the CFF, the properties you have used appear to be constant, at least, from the post

2. As far as UDF is concerned, I cannot comment until I look at it. DEFINE_ADJUST or DEFINE_EXECUTE_AT_END won't make a difference. And if you want to post process only the final solution, then use DEFINE_ON_DEMAND. But for the rest of the UDF, I need to have a look before I can say anthing.


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