CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT > Fluent UDF and Scheme Programming

Asynchronous iteration of UDS and turbulent flow?

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 15, 2021, 09:39
Default Asynchronous iteration of UDS and turbulent flow?
  #1
New Member
 
Join Date: Mar 2019
Posts: 8
Rep Power: 7
ziyixy is on a distinguished road
Hi all

I want to solve an unsteady UDS equation 100 times in one iteration of turbulent flow, e.g., the time step in UDS_UNSTEADY is 0.01 s, while the timestep in turbulent flow is 1 s. Could anybody tell me how I can achieve it? Thanks in advance.

Besides, if the timestep in UDS and flow is different, the time between C_STORAGE_R(c0,t,SV_UDSI_M1(i)) and C_STORAGE_R(c0,t,SV_UDSI_M2(i)) is 0.01 s or 1 s?

I got an idea to set the timestep in 0.01 s in both UDS and turbulent flow, and switch off the turbulent equation unless the UDS is solved every 100 times. Is it accessible and how can I do it?

Many thanks.
ziyixy is offline   Reply With Quote

Old   November 16, 2021, 00:08
Default
  #2
Senior Member
 
Alexander
Join Date: Apr 2013
Posts: 2,363
Rep Power: 34
AlexanderZ will become famous soon enoughAlexanderZ will become famous soon enough
make 1 time step
change computational scheme from transient to steady state
turn off all equation except UDS
run 100 iteration
turn on flow equation
switch to transient

repeat workflow

you can script it in journal file and run automatically using execute commands
or there are more complex solutions using scheme language
__________________
best regards


******************************
press LIKE if this message was helpful
AlexanderZ is offline   Reply With Quote

Old   November 18, 2021, 08:58
Default
  #3
New Member
 
Join Date: Mar 2019
Posts: 8
Rep Power: 7
ziyixy is on a distinguished road
Quote:
Originally Posted by AlexanderZ View Post
make 1 time step
change computational scheme from transient to steady state
turn off all equation except UDS
run 100 iteration
turn on flow equation
switch to transient

repeat workflow

you can script it in journal file and run automatically using execute commands
or there are more complex solutions using scheme language


Thanks Alexander. I attached the UDS equation, which is vortex sound equation. The p is acoustic pressure. Due to it contains an unsteady term, I cannot switch to steady. Using execute commands, I found that the S0 (acoustic pressure) remains unchanged when turning off flow/turbulence equations. I guess this is because the flux in the inlet and outlet was set as 0. I have another two questions. Thanks for your help.

1- The S0 at the inlet/outlet is satisfied to dS0/dt+gradient S0=0. How can I achieve it via UDS? Do the S0 still remains unchanged?

2-The gradient u^2 is calculated through C_UDSI(c0,t,1)= u^2, dm1=C_UDSI_G(c0,t,1)[1]. There is a redundant scalar-1 C_UDSI(c0,t,1). If I turn off the scalar-1 equation, the contour of S0 seems unphysical compared to keeping scalar-1 solved. When the scalar-1 equation turns on, the flux function, unsteady function, source of the scalar-1 is none, and the diffusivity is 0, the divergence error occurs. However, when setting diffusivity of scalar-1 is 1, it runs well and the contour of s0 can be more related to real conditions. So, how should I do?
ziyixy is offline   Reply With Quote

Reply

Tags
asynchronous iteration, udf, uds

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to define turbulent diffusion coeff. for UDS John FLUENT 4 October 16, 2015 12:38
Calculate UDS flux through the wall ananth_01 FLUENT 0 August 5, 2013 07:33


All times are GMT -4. The time now is 02:45.