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UDF for source term in momentum equation

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Old   November 4, 2004, 04:50
Default UDF for source term in momentum equation
  #1
Enrico
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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 x-component 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; }

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Old   November 4, 2004, 05:50
Default Re: UDF for source term in momentum equation
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Andrew Garrard
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you haven't defined A?
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Old   November 5, 2004, 03:26
Default Re: UDF for source term in momentum equation
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Sun
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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

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Old   November 6, 2004, 04:26
Default Re: UDF for source term in momentum equation
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enrico
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A is a constant
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Old   November 9, 2004, 04:27
Default Re: UDF for source term in momentum equation
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Bowling
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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
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Old   November 10, 2004, 06:06
Default Re: UDF for source term in momentum equation
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enrico
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Hi ,Bowling , but why dS[eqn]=0 ? dS[eqn]=dS/dU
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Old   November 12, 2004, 00:58
Default Re: UDF for source term in momentum equation
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Bowling
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You are misunderstand. dS[eqn] in here means d(source)/d(your parameter) eg. x-momentum, 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
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Old   November 13, 2004, 03:33
Default Re: UDF for source term in momentum equation
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enrico
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Hi Bowling , should i use UDS for calculating dS[eqn] ?
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Old   November 15, 2004, 00:20
Default Re: UDF for source term in momentum equation
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Bowling
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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
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Old   May 30, 2014, 11:34
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  #10
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Ke Wu
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itsme_kit is on a distinguished road
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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