Udf for boundary condition

dexter · April 4, 2019, 08:20

Hi
Is there a way to change uniform wall temperature condition to uniform heat flux boundary condition using UDF based on the value of residuals?
i.e. if my solution converges for uniform wall temperature condition then i want to change the boundary condition to uniform heat flux boundary condition.
Its a transient simulation.
Thanks

pakk · April 4, 2019, 11:46

Is there any reason why you would want to do this?

In a steady state calculation, I could understand it. You want to do a simulation with uniform wall temperature, if it converges then save the result, change the BC and run again.

But in a transient calculation, it makes no sense. Why would you change your BC after 3 seconds if it converges well, and after 6 seconds if it converges slower?

AlexanderZ · April 4, 2019, 23:33

it is possible.
Actually you don't need UDF for this, scheme language and TUI commands are enough
1. get residual value
2. change boundary condition

using scheme+UDF is also possible

best regards

dexter · April 5, 2019, 01:47

Quote:

Originally Posted by pakk

Is there any reason why you would want to do this?

In a steady state calculation, I could understand it. You want to do a simulation with uniform wall temperature, if it converges then save the result, change the BC and run again.

But in a transient calculation, it makes no sense. Why would you change your BC after 3 seconds if it converges well, and after 6 seconds if it converges slower?

Thanks for your reply.
I want to study the effect of sudden change in boundary condition.
Also, will it have same effect if i change the boundary condition manually or using UDf?

AlexanderZ · April 5, 2019, 01:49

same effect

best regards

dexter · April 5, 2019, 01:56

Quote:

Originally Posted by AlexanderZ

it is possible.
Actually you don't need UDF for this, scheme language and TUI commands are enough
1. get residual value
2. change boundary condition

using scheme+UDF is also possible

best regards

Can you elaborate a little bit about how to proceed?

Thanks

AlexanderZ · April 5, 2019, 03:02

Quote:

Is there a way to change uniform wall temperature condition to uniform heat flux boundary condition using UDF based on the value of residuals?

what residuals are you talking about?

best regards

dexter · April 5, 2019, 07:37

Quote:

Originally Posted by AlexanderZ

what residuals are you talking about?

best regards

Actually, I should have said based on flow time not residual.

pakk · April 10, 2019, 12:04

Then you should use journal files.
Find the command to run the simulation for 4 seconds.
Find the command to change the BC.
Find the command to run the simulation for 3 more seconds.

Put these commands in a journal file, and let Fluent run the journal file.

No need for UDFs.

dhiraj kumar · February 22, 2022, 03:37

hello everyone. I have a solar receiver in which at outer surface of the receiver i have to apply non-uniform heat flux [cosine profile - q(θ) = qnet ·
cos θ(−90 ≤ θ ≤ 90)] with radiation and convection losses to ambient. can anyone give me the idea for writing the UDF for ansys fluent for this condition. thanks !

April 4, 2019, 08:20	Udf for boundary condition	#1
dexter New Member Nitesh Kumar Join Date: May 2016 Posts: 17 Rep Power: 10	Hi Is there a way to change uniform wall temperature condition to uniform heat flux boundary condition using UDF based on the value of residuals? i.e. if my solution converges for uniform wall temperature condition then i want to change the boundary condition to uniform heat flux boundary condition. Its a transient simulation. Thanks

April 4, 2019, 11:46		#2
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	Is there any reason why you would want to do this? In a steady state calculation, I could understand it. You want to do a simulation with uniform wall temperature, if it converges then save the result, change the BC and run again. But in a transient calculation, it makes no sense. Why would you change your BC after 3 seconds if it converges well, and after 6 seconds if it converges slower? dexter likes this.

April 4, 2019, 23:33		#3
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	it is possible. Actually you don't need UDF for this, scheme language and TUI commands are enough 1. get residual value 2. change boundary condition using scheme+UDF is also possible best regards dexter likes this.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to setup the wall boundary condition of maxwell_slip_velocity_x_full UDF?	ailee0303	Fluent UDF and Scheme Programming	5	November 12, 2024 22:37
write a UDF to give a velocity boundary condition at an interior face	Tharanga	Fluent UDF and Scheme Programming	19	August 5, 2018 05:29
Define_profile UDF for Transient Heat flux boundary condition	Amoljoshi	Fluent UDF and Scheme Programming	2	June 20, 2018 22:55
map outlet boundary profile as an inlet condition using UDF	Daniel_Khazaei	Fluent UDF and Scheme Programming	2	June 20, 2016 12:53
udf for dpm boundary condition	ucmaen	Fluent UDF and Scheme Programming	0	July 15, 2014 14:33

April 5, 2019, 01:49		#5
AlexanderZ Senior Member Alexander Join Date: Apr 2013 Posts: 2,363 Rep Power: 34	same effect best regards

April 10, 2019, 12:04		#9
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	Then you should use journal files. Find the command to run the simulation for 4 seconds. Find the command to change the BC. Find the command to run the simulation for 3 more seconds. Put these commands in a journal file, and let Fluent run the journal file. No need for UDFs.

February 22, 2022, 03:37		#10
dhiraj kumar New Member dhiraj Join Date: Nov 2021 Posts: 6 Rep Power: 5	hello everyone. I have a solar receiver in which at outer surface of the receiver i have to apply non-uniform heat flux [cosine profile - q(θ) = qnet · cos θ(−90 ≤ θ ≤ 90)] with radiation and convection losses to ambient. can anyone give me the idea for writing the UDF for ansys fluent for this condition. thanks !