[deo]

hi guys,

I am solving a combustion problem involving ch4 (2 step model), and need the gradient of the species mass fraction for postprocessing. A simple UDF is used to extract the date with the following macro: C_YI_G(c,t,i). However, FLUENT compiles the UDF only for i = 0. When i is 1, 2, 3, or 4, the UDF does not compile. I get an error message instead. Any suggestions on how to solve this problem?

[aliemadi]

for 2step CH4 reaction you have 6 species. so for i=0-4 you can access to C_YI_G. for i=5 which refer to N2 you cant access to its gradient because its mass fraction calculated by algebraic equation not transport equation.

type in the console the following commands:
solve>set>expert
reply yes to question keep memory from being freed?
define>models>species
reply yes to question save-gardients?

[mahdi-united]

Originally Posted by aliemadi

for 2step CH4 reaction you have 6 species. so for i=0-4 you can access to C_YI_G. for i=5 which refer to N2 you cant access to its gradient because its mass fraction calculated by algebraic equation not transport equation.

type in the console the following commands:
solve>set>expert
reply yes to question keep memory from being freed?
define>models>species
reply yes to question save-gardients?

hi


i type this command but not work

how to store the species mass fraction gradients in fluent?
what is the its command?

[LuckyTran]

you don't type solve>set>expert but actually solve/set/expert or solve set expert

if you still have trouble, hit return/enter and all the available commands will pop up. /solve will be one of them. type solve [enter] and then [enter] again to see all the commands at the next level. /set will be one of them. Rinse and repeat.

If that still doesn't work then record a video. Either you don't have a keyboard or you don't have a monitor, or you're not using Fluent.

[mahdi-united]

Originally Posted by LuckyTran

you don't type solve>set>expert but actually solve/set/expert or solve set expert

if you still have trouble, hit return/enter and all the available commands will pop up. /solve will be one of them. type solve [enter] and then [enter] again to see all the commands at the next level. /set will be one of them. Rinse and repeat.

If that still doesn't work then record a video. Either you don't have a keyboard or you don't have a monitor, or you're not using Fluent.

no i know how to type this command but actually everything i do , species mass fraction gradients does not store and fluent crashes i'm hanged

[vinerm]

In a pressure-based solver, the command

solve set expert

to keep memory from being freed will not provide access to species gradient. That command works for other fields but not for species. For species, you have to either use UDF or (rpsetvar 'species/save-gradients? #t)

[mahdi-united]

Originally Posted by vinerm

In a pressure-based solver, the command

solve set expert

to keep memory from being freed will not provide access to species gradient. That command works for other fields but not for species. For species, you have to either use UDF or (rpsetvar 'species/save-gradients? #t)

my friend
this command:
(rpsetvar 'species/save-gradients? #t) is equal to define/models/species/save-gradients? (yes)
and i enter this commands and not work

[vinerm]

Yes, you can use TUI command as well. But what is implied by command not working? Does the mass fraction gradient not show up under the Derivatives? Or they do show up but the values are always 0? If it is the latter, do check if your cell zone is Fluid and not Solid under Type.

[mahdi-united]

Originally Posted by vinerm

Yes, you can use TUI command as well. But what is implied by command not working? Does the mass fraction gradient not show up under the Derivatives? Or they do show up but the values are always 0? If it is the latter, do check if your cell zone is Fluid and not Solid under Type.

no. the mass fraction gradients (dmassfraction/dx , ...) doesnt show up under the derivatives contour

furthermore !!!! after the entering command

before 1st iteration fluent crashes and does not perform the calculation



one question can i use the C_UDSI_G instead C_YI_G?
C_UDSI(..) = C_YI


and another question, value of C_UDSI=C_YI is correct in output but when i using the C_UDSI_G, values is different and unreasonable!! why???

[vinerm]

If Fluent gets hung after using the command to save species gradient then, as stated earlier, there is problem with the case. It will not help you in any way to proceed further. You may get some results but those will most likely be incorrect.

First of all, what is the objective of fetching the species gradients? There are very few requirements where you need species gradients with spatial coordinates.

Secondly, just by setting value of a scalar equal to mass fraction you will not be able to fetch the gradients. Since you already have values for mass fractions, you can directly determine the gradient using any of the methods, Green-Gauss or least square. However, as mentioned earlier, if Fluent is not showing mass fraction gradient despite issuing the command, there is something wrong with the setup. Even if you do it using the values of mass fractions, the result would most likely be incorrect.

[mahdi-united]

Originally Posted by vinerm

If Fluent gets hung after using the command to save species gradient then, as stated earlier, there is problem with the case. It will not help you in any way to proceed further. You may get some results but those will most likely be incorrect.

First of all, what is the objective of fetching the species gradients? There are very few requirements where you need species gradients with spatial coordinates.

Secondly, just by setting value of a scalar equal to mass fraction you will not be able to fetch the gradients. Since you already have values for mass fractions, you can directly determine the gradient using any of the methods, Green-Gauss or least square. However, as mentioned earlier, if Fluent is not showing mass fraction gradient despite issuing the command, there is something wrong with the setup. Even if you do it using the values of mass fractions, the result would most likely be incorrect.

i want to send my case for you but i don't know how to do it in cfd-online?
please guide me

[mahdi-united]

Originally Posted by vinerm

If Fluent gets hung after using the command to save species gradient then, as stated earlier, there is problem with the case. It will not help you in any way to proceed further. You may get some results but those will most likely be incorrect.

First of all, what is the objective of fetching the species gradients? There are very few requirements where you need species gradients with spatial coordinates.

Secondly, just by setting value of a scalar equal to mass fraction you will not be able to fetch the gradients. Since you already have values for mass fractions, you can directly determine the gradient using any of the methods, Green-Gauss or least square. However, as mentioned earlier, if Fluent is not showing mass fraction gradient despite issuing the command, there is something wrong with the setup. Even if you do it using the values of mass fractions, the result would most likely be incorrect.

i saw your message but i dont know where is knowcfd in gmail
why don't send your email address?
mahdi1372rs@gmail.com

[vinerm]

Look at the attached image.

[mahdi-united]

Originally Posted by vinerm

Look at the attached image.

sdfsdfasdfs

[vinerm]

The image I shared shows the option to attach files; marked by red rectangle. You have to look for this when you are writing a post. Just above the writing area, you will notice all the options. Look for the one that I marked with rectangle.

[mahdi-united]

ok found it

this is my fluent case

but size is more than 195kb

[vinerm]

It appears that you forgot to attach the file. You have to first choose and then click on Upload.

[mahdi-united]

the message appear: your filesize exceed from 195 kb

[mahdi-united]

Originally Posted by vinerm

It appears that you forgot to attach the file. You have to first choose and then click on Upload.

do you receive my email??

[vinerm]

After initializing the case and issuing the command

(rpsetvar 'species/save-gradients? #t)

I could see that the gradients become available under Contours. Look at the attached image.