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

DEFINE_UDS_UNSTEADY for Multiphase,apu,su meaning

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

Reply
 
LinkBack Thread Tools Display Modes
Old   December 7, 2006, 12:22
Default DEFINE_UDS_UNSTEADY for Multiphase,apu,su meaning
  #1
Anton
Guest
 
Posts: n/a
Hello Everybody!

Do you have experience with DEFINE_UDS_UNSTEADY for _multiphase_ flows?

In the FLUENT UDF manual, paragraph 2.7.4,

we see the approximaton for the unsteady term for UDS:

[unsteady term] = = -( (rho*phi)^(n) - (rho*phi)^(n-1) )/delta_t * delta_V = = apu + su,

where

apu = -rho * phi^(n) * delta_V / delta_t, su = -rho * phi^(n-1) * delta_V / delta_t.

^ here means the time step, not the power, of course.

on the other hand, the natural idea to discretize the unsteady term is:

apu = -rho^(n) * phi^(n) * delta_V / delta_t, su = -rho^(n-1) * phi^(n-1) * delta_V / delta_t.

FLUENT's default is

apu = -rho^(n-1) * phi^(n) * delta_V / delta_t, su = -rho^(n-1) * phi^(n-1) * delta_V / delta_t,

though. The question is why does FLUENT take density values for calculating apu from the previous time step and not from the current time step?

Thank you very much in advance!!

  Reply With Quote

Old   December 11, 2006, 10:14
Default Re: DEFINE_UDS_UNSTEADY for Multiphase,apu,su mean
  #2
Anton
Guest
 
Posts: n/a
okay, i've found it out by myself. This is addressed in "FLUENT defects", ID 38858.

It says it is an error in the FLUENT and it is fixed in version 6.3.1.

cheers!

  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Physical meaning of pressure in pressure eqn dontknow Main CFD Forum 2 August 30, 2010 10:12
What's meaning of UDF FUNCTION zhaoxinyu Fluent UDF and Scheme Programming 0 March 31, 2010 08:04
what is the meaning of patching shyam FLUENT 1 July 29, 2008 06:25
want to know meaning Sangamesh CD-adapco 0 May 15, 2007 05:15
What's the meaning of "combustion scalar"and.... cfdbeginner CFX 0 November 27, 2003 09:02


All times are GMT -4. The time now is 23:39.