
[Sponsors] 
November 4, 2004, 05:50 
UDF for source term in momentum equation

#1 
Guest
Posts: n/a

Hi all I write a UDF for source term in momentum equation this source term is : A.( du/dx) , where u is the xcomponent of the velocity ...
please can somebody tell me what is the mistacke I have do in this UDF DEFINE_SOURCE(xmom_source, c, t, dS, eqn) { real source; source = A*C_DUDX(c,t); return source; } 

November 4, 2004, 06:50 
Re: UDF for source term in momentum equation

#2 
Guest
Posts: n/a

you haven't defined A?


November 5, 2004, 04:26 
Re: UDF for source term in momentum equation

#3 
Guest
Posts: n/a

Not only that you have not defined A, but also you have to add one more statement namely:
dS[eqn]=0; Good Luck to you. Sun 

November 6, 2004, 05:26 
Re: UDF for source term in momentum equation

#4 
Guest
Posts: n/a

A is a constant


November 9, 2004, 05:27 
Re: UDF for source term in momentum equation

#5 
Guest
Posts: n/a

Yes, A is a constant but you must define it. for example; DEFINE_SOURCE(xmom_source, c, t, dS, eqn) { real source; int A; A=22; source = A*C_DUDX(c,t); dS[eqn]=0;
return source; } "A" can be real or integer. It is up to you. Hope I can help you. Bowling 

November 10, 2004, 07:06 
Re: UDF for source term in momentum equation

#6 
Guest
Posts: n/a

Hi ,Bowling , but why dS[eqn]=0 ? dS[eqn]=dS/dU


November 12, 2004, 01:58 
Re: UDF for source term in momentum equation

#7 
Guest
Posts: n/a

You are misunderstand. dS[eqn] in here means d(source)/d(your parameter) eg. xmomentum, your parameter is U your source is A*(dU/dX), so dS[eqn] is second derivative of dU/dX equal d^2U/dX^2. Diff your source by your parameter.
dS[eqn] is the way to define your source solving. I don't know how to explain. You can read more infomation in fluent document. Bowling 

November 13, 2004, 04:33 
Re: UDF for source term in momentum equation

#8 
Guest
Posts: n/a

Hi Bowling , should i use UDS for calculating dS[eqn] ?


November 15, 2004, 01:20 
Re: UDF for source term in momentum equation

#9 
Guest
Posts: n/a

I don't think so. It is the condition in DEFINE_SOURCE. It is the way to solve in the finite volume method not a scalar.
Bowling 

May 30, 2014, 12:34 

#10 
Senior Member
Join Date: Jan 2012
Posts: 197
Rep Power: 14 
how do we know this formula: source = A*C_DUDX(c,t);
I have a equation for velocity gradient: dudz=const However, I have no idea how to transfer my equation into this kind of form: source = A*C_DUDX(c,t); Thanks 

Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
add source term to energy equation by udf  tomas  Fluent UDF and Scheme Programming  7  September 10, 2013 03:08 
Derivation of Momentum Equation in Integral Form  Demonwolf  Main CFD Forum  2  October 29, 2009 20:53 
UDF Timedependent term in source  Ronnfors  FLUENT  0  October 16, 2009 12:25 
UDF Source Term Units?  Brian  FLUENT  1  October 24, 2005 10:15 
bouyancy term in epsilon equation  Michael  Main CFD Forum  1  June 25, 1999 11:20 