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

Laminar unsteady flow convergence

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 15, 2009, 13:00
Default Laminar unsteady flow convergence
  #1
New Member
 
pinho
Join Date: May 2009
Posts: 22
Rep Power: 17
jpinho is on a distinguished road
Hi there,

Im doing a simulation for a heat exchanger where i heat water inside an aluminum block. The flow rate is low i assume laminar model.

When I try to solve it steady, the solutions converge and i get fine results. but when i tried to do it unsteady they dont.

I started with a condition where there was no heat coming to the water, and then i assumed a heat generation of 20000 w/m2 going towards the water with 20 time steps of 3 seconds interval solving on maximum 40 iterations each.

In the beginning the water starts heating but after 6 time steps it doesn't converge... it prompts error on minimum temperature 1k...

any idea?

thanks
jorge
jpinho is offline   Reply With Quote

Old   May 15, 2009, 15:43
Default
  #2
Member
 
Akour
Join Date: May 2009
Posts: 79
Rep Power: 17
ak6g08 is on a distinguished road
hi jorge,

minimum temperature 1kelvin I think means that somewhere in your solution, you are effectively getting values of temperature under absolute zero, which is physically impossible and thus fluent doesnt like it.

any error that fluent pops up is an error from your grid generation/boundary definitions or boundary conditions in my experience...try changing the boundary conditions around to pinpoint the error, i.e. make all your walls fixed temperature boundary conditions, and then one by one make them fixed flux (at zero) boundary conditions to see when the error comes up and that will tell you if its a boundary issue which i suspect it is. otherwise, try decreasing your timestep to see if that makes a difference.. hope that helps

akour
ak6g08 is offline   Reply With Quote

Old   May 19, 2009, 11:16
Default
  #3
New Member
 
pinho
Join Date: May 2009
Posts: 22
Rep Power: 17
jpinho is on a distinguished road
Thanks Akour,

I found the problem.
The mesh quality was really poor and there was a discontinuity in some points of the geometry.. i will start it over..

thanks again
jorge
jpinho is offline   Reply With Quote

Reply

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
Validation for laminar Disperse phase flow shashwat Main CFD Forum 0 April 4, 2008 03:20
Laminar flow or Turbulent flow mech FLUENT 0 January 27, 2007 19:51
laminar and turbulent flow in one simulation msna FLUENT 0 January 27, 2007 18:35
Unsteady flow structures - time development diaw Main CFD Forum 4 December 13, 2005 06:15
On the unsteady flow. mini FLUENT 0 January 18, 2005 04:33


All times are GMT -4. The time now is 10:13.