UDF for reading heat flux through BC

michal.s · February 28, 2018, 06:22

Hello there!

I am looking for a solution.
My domain is a fluid and a solid sphere inside - however the sphere is out of the domain (just empty space).
I need to compare temperature distribution within the sphere using 0D and 1D equations.
Therefore I need an UDF to:
1) Read the heat transferred by convection from the liquid into the wall BC with different temperature
2) Calculate the total heat gain during previous time step
3) Calculate what would be the temperature distribution for the current time step within the sphere and on its surface - wall BC inside domain. (Let's say for 0D case it would be just one value)

I have got an idea how to solve it, however I don't know how to get the value of heat flux.

I went through the manual and this forum, I don't have an answer :/

Anybody can have some idea?

pakk · March 1, 2018, 05:07

The heat flux from wall to gas (what Fluent calls "Total Surface Heat Flux") can (I think) be accessed through:

Code:

BOUNDARY_HEAT_FLUX(f,t)

(for the rest in the same way as that you access temperature by F_T(f,t).)

I did not test this, but it should work at least in Fluent 18.1. It is not mentioned in the manual, so even if it works in Fluent 18.1, the Ansys programmers might choose to change this in further versions without warning.

michal.s · March 1, 2018, 05:47

I didn't know about it, I'll try, thanks!

Right now in TUI I am defining a variable:
1) (rp-var-define 'name 0.0 'real #f)
2) (rpsetvar 'name (pick-a-real "/repor/fluxes/heat-transfer no wall () no"))

In my DEFINE_PROFILE UDF I am calculating all values I need and the temperature at the boudary using variable "name".
Second SCHEME command is executed once in each time-step in order to update its value.

Right now it works, but the temperature calues are not calculated properly (I have to find a mistake, but I am glad that the behaviour is OK)
However I it would be OK to solve it more "elegant"

February 28, 2018, 06:22	UDF for reading heat flux through BC	#1
michal.s Member Michal Join Date: May 2017 Posts: 35 Rep Power: 9	Hello there! I am looking for a solution. My domain is a fluid and a solid sphere inside - however the sphere is out of the domain (just empty space). I need to compare temperature distribution within the sphere using 0D and 1D equations. Therefore I need an UDF to: 1) Read the heat transferred by convection from the liquid into the wall BC with different temperature 2) Calculate the total heat gain during previous time step 3) Calculate what would be the temperature distribution for the current time step within the sphere and on its surface - wall BC inside domain. (Let's say for 0D case it would be just one value) I have got an idea how to solve it, however I don't know how to get the value of heat flux. I went through the manual and this forum, I don't have an answer :/ Anybody can have some idea?

March 1, 2018, 05:07		#2
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	The heat flux from wall to gas (what Fluent calls "Total Surface Heat Flux") can (I think) be accessed through: Code: BOUNDARY_HEAT_FLUX(f,t) (for the rest in the same way as that you access temperature by F_T(f,t).) I did not test this, but it should work at least in Fluent 18.1. It is not mentioned in the manual, so even if it works in Fluent 18.1, the Ansys programmers might choose to change this in further versions without warning.

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March 1, 2018, 05:47		#3
michal.s Member Michal Join Date: May 2017 Posts: 35 Rep Power: 9	I didn't know about it, I'll try, thanks! Right now in TUI I am defining a variable: 1) (rp-var-define 'name 0.0 'real #f) 2) (rpsetvar 'name (pick-a-real "/repor/fluxes/heat-transfer no wall () no")) In my DEFINE_PROFILE UDF I am calculating all values I need and the temperature at the boudary using variable "name". Second SCHEME command is executed once in each time-step in order to update its value. Right now it works, but the temperature calues are not calculated properly (I have to find a mistake, but I am glad that the behaviour is OK) However I it would be OK to solve it more "elegant"