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

Elliptic equation UDF

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 28, 2005, 11:45
Default Elliptic equation UDF
  #1
dieter
Guest
 
Posts: n/a
Hi,

Has anyone ever implemented in fluent an elliptic differential equation (helmholtz) of the form: a*LAPLACIAN(phi)=phi-1, with phi the scalar field that has to be resolved and a a constant? I tried to program it in a UDF using User defined scalars (UDS), but it didn't work. the solution is not stable (as I expected). does anyone knows a better implementation? Could anyone help me? its urgent!

this is how I programmed it now:

in the ADJUST function:

C_UDSI(c,t,F)=MAX(MIN(C_UDSI(c,t,F),const_1),const _2);

C_UDSI(c,t,DFDX) = C_UDSI_G(c,t,F)[0]; /*with this you can calculate the derivative of an UDS, [0] denotes the x-component*/ C_UDSI(c,t,DFDY) = C_UDSI_G(c,t,F)[1]; C_UDSI(c,t,DFDZ) = C_UDSI_G(c,t,F)[2]; C_UDSI(c,t,D2FDX2) = C_UDSI_G(c,t,DFDX)[0]; C_UDSI(c,t,D2FDY2) = C_UDSI_G(c,t,DFDY)[1]; C_UDSI(c,t,D2FDZ2) = C_UDSI_G(c,t,DFDZ)[2];

C_UDSI(c,t,F) =a*(C_UDSI(c,t,D2FDX2)+ C_UDSI(c,t,D2FDY2)+ C_UDSI(c,t,D2FDZ2))+1.;

thanks for your help Dieter
  Reply With Quote

Old   March 7, 2005, 06:28
Default Re: Elliptic equation UDF
  #2
mcfiggis
Guest
 
Posts: n/a
I think you've mistaken Fluent for Mathcad. To solve this equation:

1. Turn off the convective flux. 2. Set the diffusivity of the scalar to a. 3. Set the source term for the UDS to C_UDSI(c,ct,0)-1, which you'll have to linearise: dS[eqn] = 1.

All these things can be found in the UDF manual.

  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
mass flow in is not equal to mass flow out saii CFX 12 March 19, 2018 06:21
Implicit elliptic pressure field equation. TheBoyce Main CFD Forum 2 June 3, 2011 14:08
UDF for Powell vortex sound equation dipole Fluent UDF and Scheme Programming 0 October 8, 2010 10:48
udf temperature/velocity profile-> equation problems roka1mtr FLUENT 2 August 25, 2009 05:44
UDF sourse term for VOF equation ROOZBEH FLUENT 5 April 22, 2003 07:56


All times are GMT -4. The time now is 03:15.