CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Fluent udf--assigning u-velocity to uds

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

LinkBack Thread Tools Search this Thread Display Modes
Old   August 10, 2009, 15:46
Lightbulb Fluent udf--assigning u-velocity to uds
Senior Member
Troy Snyder
Join Date: Jul 2009
Location: Akron, OH
Posts: 207
Rep Power: 17
tas38 is on a distinguished road
I was working with a Fluent udf that involved assigning the flow primitive, u-velocity, to a uds.


However, when I plot the user-defined scalar within Fluent, the value is not close to the theoretical value for u-velocity. Additionally, the plot of of the uds looks does not match the plot of X-velocity.

Has anyone encountered this problem before?

I do not want to continue writing my udf if the assignments to user-defined scalars may not be accurate.

I hooked the udf to a simple test case of couette flow. The visous flow is between a stationary bottom plate and a top plate moving the x-direction at 1 m/s. The distance between the plates is 0.001 meters. Taking a Line Rake of points along the midline of the geometry, X-velocity ranges from 0 at the bottom stationary plate to 1 at the top plate--this is in agreement with theory. User-defined scalar 0, however, ranges from 0.4491 at the bottom plate to 0.5168 at the top plate?
tas38 is offline   Reply With Quote

Old   August 11, 2009, 10:41
Senior Member
Join Date: Mar 2009
Posts: 133
Rep Power: 16
coglione is on a distinguished road
Hello Troy

be aware that if you define a UDS Fluent will solve a transport equation for this scalar. Therefore C_UDSI(c,t,0)=C_U(c,t) is only true at the moment this assignment is executed in your udf (which one do you use?) but values will be updated every iteration/timestep performed.

coglione is offline   Reply With Quote


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
UDF in Fluent Andrew Fluent UDF and Scheme Programming 5 March 7, 2016 03:38
DPM UDF particle position using the macro P_POS(p)[i] dm2747 FLUENT 0 April 17, 2009 01:29
UDF velocity and temperature Raj FLUENT 3 February 1, 2009 18:29
Pb with simple Fluent UDF example for inlet francois FLUENT 0 October 9, 2008 10:34
Urgent! Help on UDF to set inlet velocity Ray Hong FLUENT 4 December 30, 2005 12:32

All times are GMT -4. The time now is 14:38.