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

#1 
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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 
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you haven't defined A?


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

#3 
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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 
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A is a constant


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

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


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

#9 
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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, 11:34 

#10 
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Ke Wu
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Posts: 179
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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 

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